The hydrodynamic model FLO-2D (O'Brien et al. 1993) was applied to calculate the flow transformation in the valley. The model is based on the solution of the Saint-Venant equations, in which the flow characteristics are averaged over depth (the so-called "shallow water" equations) (Cunge et al. 1980). The motion of debris flow in FLO-2D model is simulated under the assumption that it moves as Bingham (viscoplastic) liquid (O'Brien et al. 1993). If the detail rheological analysis of debris flow and deposits cannot be made, the authors of the model propose the following parameters from Table 1.

For identification of the Buzulgan rockslide dynamics, route surveys have been carried out since 2020, a month after the movement. The relief data was obtained using a UAV DJI Mavic Pro Platinum. The average spatial resolution of the surveys was 12.2 cm/pixel. The images were processed using the Agisoft Metashape program software [https://www. geoscan.aero/ru/software/agisoft/metashape\_pro]. In areas where a large number of trees were identified, automatic classification was performed for a dense point cloud for the "high vegetation" class. Carrying out this operation made it possible to avoid the creation of a "false dam" in forested areas. Thus, a high-resolution digital surface model (DSM) was created, which took into account the location of the tray and buildings. After correction, all relief data were interpolated into the 3 × 3 m computational grid of the model.

#### 4.4 Results and Discussion

The discharge of a possible debris flow at the outlet of the landslide site according to UAV data from 2020 was 1019 m3 /s, with an input of 700 m3 /s. At the top of the alluvial fan, the flow discharges vary approximately from 1 to 18% depending on the parameters set of the rheological block in the FLO-2D model (Table 2).

The maximum flow velocities on the alluvial fan were observed in the channel of the Gerkhozhan-Su River and changed for different variants of rheological parameters: a) -9.3 m/s, b) -10.7 m/s, c) -11.5 m/s, d) -10.7 m/s. The obtained values turned out to be slightly lower than the values if there was no blockage of the channel at the road bridge site (Kurovskaia et al. 2022).

The flow velocity on the fan itself varied from 1.5 to 5 m/ s and higher. The flow depth at the alluvial fan, on average, for all variants of rheological parameters changed from 1 to 9 m, which was higher than for the modeling without the channel blockage by debris flows (Kurovskaia et al. 2022). The average inundation zone on the alluvial fan was 0.385 km2 . The largest zone was obtained using the variant of parameters a), the smallest—c), the difference between them was about 10%. The distinction between inundation zones for this case and in the absence of blockage of the bridge was about 26%. At the same time, the debris flow covered both along the left bank of the Gerkhozhan-Su River and along the right bank. According to the simulation results, residential buildings, buildings of the of the Elbrus region administration, several schools, and a kindergarten were

Table 1 Parameters for calculating the stress of plastic flow and viscosity as a function of sediment concentration (O'Brien and Julien 1988)

Note: G Glenwood, ANS Aspen natural soil

located in the flood prone zone, despite the debris flow observed in August 2022 passed exclusively through the flume. In 2021, the flume was cleared; therefore, the inundation hazard was reduced for some time. However, after debris flow in August 2022, the flume was partially filled with deposits again. Thus, the simulation reproduced the worst situation (Fig. 10).

#### 5 Conclusion

The valley of the Gerkhozhan-Su River (a tributary of the Baksan River) in the Northern Caucasus is one of the most debris flow-prone areas in Russia. One of the factors of catastrophic debris flows in the valley of the river

Fig. 10 Planar distribution of debris flow velocities on the alluvial fan of the Gerkhozhan-Su River using the FLO-2D model 1) calculation variant a), 2) calculation variant c)

Gerkhozhan-Su is the Buzulgan ladslide. Earlier, as a result of the landslide movement, the debris flows entrained additional solid material and impulse.

The Buzulgan landslide was formed within the Pshekish-Tyrnyauzskaya suture, which is a narrow (2–3 km) tectonic zone affected by derives of faults.

The modern destabilization of the slope massif has been observed since March 2020. The peak of the landslide activity was in August 2020. At this time, the movement in the frontal part of the landslide was up to 120 m at an average speed of 40 m/day (~1.67 m/h). The movement in the upper part of the landslide during this time was 290 m at an average speed of up to 97 m/day (~4 m/h). In total, the upper part of the landslide shifted by ~430 m from 07.08.2020 to 14.08.2020. The total volume of the Buzulgan landslide is estimated at 7.0–7.2 mln m3 .

As a result of the movement of the landslide in August 2020, the bed of the Gerkhozhan-Su River was blocked for 480 m. However, the river quickly eroded a new channel in a landslide dam, composed of disintegrated debris. As a result, no large-scale landslide-dammed lake was formed in 2020. The new river channel was shifted 95–100 m towards the left side of the valley.

Currently, the role of the Buzulgan landslide in increasing the debris flow hazard is the possible formation of a new landslide-dammed lake when a debris flow originate sup stream in the valley. The subsequent breakthrough of such a landslide-dammed lake may be accompanied by the formation of a high debris flow surge. Such a scenario could be catastrophic for the Tyrnyauz town, which is located just 2 km down the valley. Thus, the continuation of the study of the Buzulgan landslide and organization of monitoring at this site are critically important.

The paper presents the results of modeling based on the FLOVI and FLO-2D PRO software package. The FLOVI program, which is based on the equations of the transportshift model, was used to calculate the flow characteristics at the site where debris flow crosses the Busulgan landslide. Modeling of flow transformation in the valley was performed using a two-dimensional hydrodynamic model FLO-2D. The sensitivity of the hydrodynamic model to the rheological parameters was shown, so the difference in debris flow discharges at the alluvial fan varied from 1 to 18%, the difference of inundation zone was about 10%. Modeling on the cone itself was carried out for the case of the channel blockage in the bridge area by debris flow deposits or because of the collapse of the bridge. In this case, the area of the flood zone is 26% larger. The results obtained show the effectiveness of the applied complex of models.

#### References

for describing the activity of a landslide. Bull Intern Assoc Eng Geol 47:53–57

Open Access This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/ licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

# A Risk Evaluation Method of Unstable Slopes Using Multipoint Tilting Sensors

Makoto Fukuhara, Lin Wang, Shangning Tao, Zhijun Tang, Wenjian Tang, Linyao Dong, and Zhongjie Fan

#### Abstract

Slope monitoring and early warning systems (EWS) are a promising approach toward mitigating landslide-induced disasters. Many large-scale sediment disasters result in the destruction of infrastructure and loss of human life. The mitigation of vulnerability to slope and landslide hazards will benefit significantly from early warning alerts. The authors have been developing monitoring technology that uses a Micro Electro Mechanical Systems (MEMS) tilt sensor array that detects the precursory movement of vulnerable slopes and informs the issuance of emergency caution and warning alerts. In this regard, the determination of alarm thresholds is very important. Although previous studies have investigated the recording of threshold values by an extensometer which installation at appropriate sites is rather difficult. The authors prefer tilt sensors and have proposed a novel threshold for the tilt angle, which was validated in this study. This threshold has an interesting similarity to the previously reported values using viscous models. Additionally, multi-point monitoring has recently emerged and allows for many sensors to be deployed at vulnerable slopes without disregarding the slope's precursory local behavior. With this new technology, the detailed spatial and temporal variation of the behavior of vulnerable slopes can be determined as the displacement proceeds toward failure.

#### Keywords

Disaster mitigation · Early warning · Risk evaluation · Slope failure · Warning threshold

M. Fukuhara · L. Wang (✉) · S. Tao · Z. Tang Chuo Kaihatsu Corporation, Technology Center, Tokyo, Japan e-mail<EMAIL_ADDRESS><EMAIL_ADDRESS><EMAIL_ADDRESS>jp<EMAIL_ADDRESS>
W. Tang · L. Dong · Z. Fan Changjiang River Scientific Research Institute, Changjiang Water Resource Commission, Wuhan, China e-mail<EMAIL_ADDRESS>
#### 1 Introduction

Slope instability is a natural hazard that exerts a profound influence on the operation and reliability of infrastructure. Unlike engineered structures, natural slopes are not designed for safe performance. As a consequence of natural processes, slopes have heterogeneous material properties. Moreover, slopes are prone to erosion, and their gradient changes with time. Underground hydrology is hardly captured in practical engineering. Therefore, quantitatively assessing the extent of slope stability is very difficult in practical situations. Although the movement of landslide masses, which has been slow in conventional studies, is already a major threat to human activities, rapid and unpredictable slope failure triggered by gravity or heavy rain is more hazardous because it may instantaneously result in an enormous loss of human life and the destruction of infrastructure. However, predicting the abrupt failure of slopes to avoid damage is still difficult. Communities in mountain regions are particularly prone to this type of damage. The situation is more serious for transportation infrastructure because its function can be entirely disrupted by a single slope failure (Lee et al. 2013; Sartori et al. 2003). Ongoing global climate change increases the likelihood of heavy and concentrated rainfall, which results in more rainfall-induced slope failures.

As stated above, the mitigation of landslide disasters is difficult and the available funding for conducting elaborate site investigations is far too little. Practitioners have been trying to improve safety by developing slope monitoring and early warning system (EWS) technologies with the objective of predicting slope failure in advance based on the observed slope behavior and mitigating the extent of damage (Medina-Cetina and Nadim 2008). The United Nations International Strategy for Disaster Reduction (UN-ISDR 2006) advocates that EWS should "empower individuals and communities threatened by hazards to act within sufficient time and in an appropriate manner to reduce the possibility of

# The Author(s) 2023

I. Alcántara-Ayala et al. (eds.), Progress in Landslide Research and Technology, Volume 2 Issue 1, 2023, Progress in Landslide Research and Technology, https://doi.org/10.1007/978-3-031-39012-8\_11

Fig. 1 Schematic illustration of MEMS tiltometer sensor for early warning (Wang et al. 2017)

Fig. 2 Graphic illustration of the tilting rate as a function of time before slope failure (or stabilization) for several case studies (Uchimura et al. 2015)

personal injury, loss of life, and damage to property and the environment" (from the UN-ISDR web site).

There is a long history of prevention and mitigation of rainfall and/or scouring-induced landslides. Mechanical countermeasures to prevent slope failure have been widely used, including retaining walls and ground anchors. However, these methods can be expensive and are not always realistically applicable to all slopes of varying scales and potential risk factors. Therefore, careful monitoring of slope behavior and consequent early warning of failure provides a reasonable and slope-specific alternative.

In this paper, an early warning system for slope failure is proposed and its development is described (Fig. 1) (Wang et al. 2017). The system consists of a minimum number of low-cost sensors strategically placed on a slope, with monitoring data that are collected being transmitted via a wireless network. It is anticipated that this low-cost and simple system will provide at residents risk with access to accurate and timely precautions or warnings of slope failure.

Uchimura et al. (2015) summarized case studies of slope tilting rates during pre-failure stages obtained on several natural slope sites under natural or artificial heavy rainfall. Figure 2 presents an example of the typical monitoring data obtained, in which the tilting rate (X-axis) can be related with the time elapsed until slope failure or slope stabilization (Y-axis). Figure 3 shows the definition of the tilting rate and the time in Fig. 2, in which Ti is the time until failure or stabilization, and Ri is tilting rate.

Fig. 3 Definition of the tilting rate and the durations (Uchimura et al. 2015)

In cases where the slope failed at the position of the tilt sensor, the elapsed time is measured from the time when tilting accelerated to the time of failure. In cases where the slope did not fail but instead stabilized, the time is measured from when tilting decelerated to the time when the slope stabilized.

According to Fig. 2, the order of tilting rate observed with slope deformation varied widely, from 0.0001°/h to 10°/ h depending on several factors. The tilting rate tends to increase towards failure with a relatively short time until failure, when a higher tilting rate is observed. The observed tilting rate was >0.01°/h for all the cases in which the slope failed or nearly hour was observed before failure for a tilting rate of 0.1°/h.

Based on the past case studies, it is proposed that when the tilting rate exceeds 0.1°/h a warning of slope failure should be issued, and a precaution issued at a tilting rate of 0.01°/h, taking safety into account. Additionally, this paper explores efforts by the current authors to improve the applicability of the monitoring and early warning system. The miniature tilt sensors are modified from that currently available to be more cost-effective, smaller in size and weight, and simpler to install, maintain and operate. As a result, it is possible to install a larger number of sensors on a given slope, thereby providing greater coverage and higher data density.

Figure 4 illustrates the typical arrangement of two types of proposed sensors, with data transfer pathways also shown. Despite the advantages described above, the new type of miniature tilt sensors has relatively short radio transmission distances (~30 m in non-ideal conditions). They are arranged densely on high-risk areas of a slope, with one conventional tilt sensor unit collecting all the data of each area. The data are transmitted over greater distances (300–600 m) and uploaded to an internet server.

#### 2 Field Validation of Tilt Sensor for Slope Monitoring

Previously, MEMS tilt sensors have been used at more than 100 sites with slope instability in worldwide. Most of these slopes did not fail, but several of these slopes have failed with and without rainfall and provided important data. Based on these data, the warning threshold has been determined as 0.1°/h. In this section, various cases that have not been reported are discussed.

#### 2.1 Prevention of Secondary Disaster During Restoration of Failed Slope–Fukuoka Pref., Japan

An EWS was successfully used in 2015 in Fukuoka Prefecture, Japan. When this region received heavy rainfall during

Fukuoka (a) Plan view and sensor location.

(b) View from the sky

typhoon No. 11 "Nangka" on July 17 and 18, the slope collapsed and the local road was closed for traffic (Fig. 5). This slope comprises Funi volcanic rock of andesite karst, tuff breccia, and tuff. To safely keep one lane open for traffic during slope restoration, the slope movement was monitored by a set of tilt sensors as shown in Fig. 6. The traffic was intended to stop if the tilt sensor detected an excessive tilting rate during the slope restoration works.

Figure 6 shows the plot of the tilt angle and the rainfall data on July 21st and 22nd, shortly after the main slope

Fig. 6 Time histories of monitored data at Fukuoka site

collapse. The slope was considered to be prone to further failures during the restoration works. From 4 PM to 8 PM on July 21st, that is, immediately after the tilt sensor installation, the tilting rate of 0.083°/h was recorded and continued until 8 AM on July 22nd. Thereafter, the tilting rate accelerated to 0.89°/h, possibly owing to rainfall amounting to approximately 10 mm from 8 AM to 9 AM. Furthermore, owing to further rainfall after 11 AM, the tilting rate sharply increased to 12°/h after 12 PM and the slope finally collapsed at 12: 30 PM. Thus, the field monitoring helped control the traffic during the critical period and ensured the safety of human life.

Based on practical experiences at many sites with and without failure, the authors (2015) recommend that a warning and evacuation order should be issued at this tilting rate. Moreover, precautions may be issued at a tilting rate of 0.01°/h to ensure safety, because the time left until failure will be several hours or longer.

In the typical case wherein the surface soil thickness is 150 cm (Fig. 1) in Japan, the 0.01°/h and 0.1°/h tilting rates correspond to the displacement rates of 150 × tan (0.01°) or 150 × tan (0.1°), that is, 0.026 cm/h or 0.26 cm/h, respectively. Hence, it is extremely difficult for GPS, LIDAR, and InSAR to continuously monitor this small movement during heavy rainfall. Therefore, the authors prefer using tilt sensors. The following sections discuss the practical experience acquired at other slope-monitoring sites and used to validate the warning principle described above.

#### 2.2 Practical Tilt Sensor Monitoring in Tokyo

Because of the heavy rain associated with Typhoon No. 21 "Jebi" on October 23, 2018, a part of industrial waste landfill collapsed in Tokyo. Consequently, a part of the collapsed sediment flowed and reached the prefectural road below the slope (Fig. 7).

Accordingly, a temporary protective fence and large sandbags were placed along the road, but drastic measures against the landfill collapse were not implemented. However, it was highly likely that slope failure would reoccur during the rainy season in 2019. Hence, the Environment Bureau of the Tokyo Metropolitan Government installed three extensometers at the edge of the landfill for monitoring. Moreover, three tilt sensors were installed for research purposes.

Figure 8 shows the monitored time history of the cumulative rainfall and the tilt angles. When the rainfall, which cumulatively amounted to 38 mm, occurred before 8 PM on June 15, there was no significant change in the records of tilt sensors K-1 and K-2. Thus, the situation remained relatively stable. A few hours later, in the early morning of June

Fig. 7 Monitoring at landfill slope in Tokyo. (a) Plan view and tilt sensor locations. (b) Appearance of slope failure

Fig. 8 Recorded cumulative rainfall and tilt angles at sensor K-1 and K-2 at the site shown in Fig. 7 (June 15th and 16th)

16, the tilt angles started to increase toward infinity at 5: 10 AM (slope collapse). The tilting rate of sensor K-1 reached 0.58°/h (X axis of slope direction) at 4 AM on June 16, and sensor K-2 reached 0.20°/h (X axis of slope direction) at 3:30 AM on the same day. Because the record

of the tiltmeters accumulated in the negative direction of the X axis (toward the top of the slope), it is believed that the slope failure mechanism was associated with a circular slip (rotation).

#### 2.3 Monitoring Slope Failure at Manzawa, Yamanashi, Japan

The Manzawa area in the Yamanashi Prefecture of Japan contains a large-scale reactivation of old slope failures featuring rockfalls that involve the detachment and rapid downward movement of rock.

Because most traditional slope monitoring methods are expensive, difficult to control and may not be suitable for application in this civilian area, the simple and low-cost monitoring system was deployed on a test slope to validate field performance. It should be noted that the research is supported by the Japanese Government during 2014–2017, and the following result that is reported in this paper.

Figure 9 shows the scale of Manzawa slope failure site, and Fig. 10 shows the arrangement of the multi-point tilt sensors and locations, where two types of tilt sensor were used. The arrangement interval of the sensor is designed to 5 m. A total of 66 sets of sensors were deployed.

The 66 sensor units are divided into three groups, left/ middle/right zone, and one data receiver unit and one logger/ gateway unit for internet to collect all the data from respective group as shown in Fig. 10. There were eight heavy rainfall events during summer of 2015 shown in Fig. 11, and the tilting rate averaged during each rainfall event is shown in Fig. 12. Distribution of tilting behaviors of two tears result was figured out by multi-point monitoring in Fig. 13 during 2015–2017.

Fig. 9 Area of slope failure at Manzawa site, Japan

#### 2.4 Early Warning by Using Multi-point Monitoring

Wang et al. (2017) proposed an early warning method based on single-sensor monitoring. Recently, the authors have extended the scope of slope monitoring to multi-point monitoring, which can capture both the spatial and temporal behavior of the entire slope. Additionally, multi-point monitoring can avoid erroneous warnings caused by very local

Fig. 10 Arrangement of the multi-point tilt sensors

Fig. 11 Time histories of movements in rainy days during summer of 2015

Fig. 12 Distribution of tilting rates during each rain day during summer of 2015

Fig. 13 Distribution of accumulated inclination angle during 2015–2017

slope movement and animal contact, among other causes of error. Thus, the reliability of early warning is improved.

The spacing between multiple sensors must be kept within a reasonable limit (a few meters to a few tens of meters, as in the practical cases discussed in this paper), and a new index of slope movement must be proposed in place of a single sensor's tilting rate, as in past practical cases.

Certainly, the new index must handle data at all monitoring points. Presently, the new index is assumed to be expressed as follows:

$$\mathbf{V\_{alarm}} = \sum\_{\mathbf{n}=1}^{\mathbf{n}} \left( |\mathbf{Vn}| \ast \frac{\mathbf{A}\mathbf{n}^\*}{\mathbf{A0}} \,\partial\mathbf{n} \right) \tag{1}$$

where n is the total number of tilt sensors; Vi is the tilting rate (otherwise denoted as dα/dt) in the slope direction of the ith sensor (°/h); Ai is the area covered by the ith sensor; A0 is the area covered by the entire sensor array; ∂i is the coefficient determined by the geology, geography, soil type, and vegetation conditions at the installation points. Moreover, the ∂i coefficients regard the field conditions, and their values are determined based on the results of geomaterial experiments and the assessment of geologists. Although this issue requires further investigation, ∂i = 1 is currently used in practical situations.

#### 3 Conclusion

The authors have been developing slope failure monitoring and early warning technology. This technology is characterized using MEMS tilt sensors. In earlier versions, monitoring was conducted using a single sensor. However, a multi-sensor approach was implemented in recent development. This paper introduces the most recent development of the authors' EWS based on data obtained from several sites and their interpretation. The following conclusions were drawn from this study:

As the actual plans, the authors are currently undertaking the National key R&D project of Sino-Japan "Development and demonstration of monitoring and warning technology for the rainstorm induced mountain torrent disaster chain", which takes the rainstorm-flood-landslide-debris flow disaster chain as the research object and is carrying out through international cooperation and joint research. By using the strength of the Japanese participating units in the field of disaster mechanism research and sensing technology and bring into play the advanced level of the Chinese participating units in communication technology and platform development, the results such as deeply exploring the occurrence and evolution mechanism and developing the key technologies for precise monitoring and dynamic warning of the rainstorm-induced mountain flood disaster chain are expected to be obtained. The project aims to provide scientific and technological support for the mountain flood disaster chain prevention and control, and effectively improve the theoretical and technological level of disaster prevention and reduction research between China and Japan.

Acknowledgments This research was supported by Council for Science, Technology and Innovation, "Cross-ministerial Strategic Innovation Promotion Program (SIP), Infrastructure Maintenance, Renovation, and Management". (Funding agency: NEDO) of Japan. The National Key R&D Program of China (Grant number 2021YFE0111900), and the National Natural Science Foundation of China (Grant No. 41977171, 41902300).

#### References

Lee WF, Liao HJ, Wang CH (2013) Failure analysis of a highway dip slope slide. 4th International Seminar on Forensic Geotechnical Engineering, Bangalore. pp 325–338

Open Access This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/ licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

Part III

IPL Projects, World Centres of Excellence on Landslide Risk Reduction, and Kyoto Landslide Commitment 2020

# Community Level Slope Disaster Risk Reduction Program through Multi-Scale Mapping by Mountain Ethnic Group in Northern Vietnam: Project Study by JICA/Lao Cai DARD/ITST

Nguyen Kim Thanh, Toyohiko Miyagi, Ta Cong Huy, Eisaku Hamasaki, Dinh Van Tien, and Yasuhiro Kasuya

#### Abstract

Recent advances in remote sensing have been remarkable, not only in terms of technology but also in terms of operability and price. Ethnic minorities in the mountains have historically barely survived repeated disasters. As a result, they are still living in an environment with a high risk of landslide disasters. Although the economic conditions of these residents deter their efforts to find engineering solutions to mitigate potential landslide disasters, they can adequately assess the regional conditions daily. By combining their abundant but fragmental knowledge of landslide disasters with our "Site Prediction Technology of Mapping," we are trying to develop a local community that can avoid disasters and ensures their safety.

This project focuses on mountainous areas in northern Vietnam and is a collaborative effort among Vietnamese and Japanese engineers, local governments, and international organizations. We have begun to present ALOS World 3D (AW3D) data and data acquired by Unmanned Aerial Vehicles (UAV) to residents and use them for disaster prevention and evacuation drills. This mapping process is called Communication Based Evacuation Mapping (CBEM). Despite Japan's long history of using

Institute of Transport Science and Technology, Hanoi, Vietnam

Tohoku Gakuin University, Sendai, Japan

T. Miyagi · E. Hamasaki Advantechnology Co., Ltd, Chiyoda, Japan e-mail<EMAIL_ADDRESS><EMAIL_ADDRESS>
T. C. Huy LaoCai DARD, Lao Cai, Vietnam

D. Van Tien Institute of Transport Science and Technology, Hanoi, Vietnam

Y. Kasuya JICA Vietnam, Hanoi, Vietnam e-mail<EMAIL_ADDRESS>maps to prevent disasters, it is rare for residents to use them actively, as having an engineer make and publish a map will not lead to its use by the residents. This paper introduces a series of measures taken from the creation of maps to the engagement of residents in slope disaster risk reduction.

#### Keywords

Community level · Communication Based Evacuation Mapping (CBEM) · Multi-scale mapping · Slope disaster · Mountain ethnic group · Vietnam

#### 1 Introduction: Necessity of Mountainous Slope Disaster Prevention in Mountainous Areas of Vietnam

Vietnam is located in the northern part of Southeast Asia, on the central coastal region of the Indochina Peninsula. It is long in the north-to-south direction, from 8 degrees north latitude to 23.5 degrees north latitude. The Annan Mountains run parallel to the coast. Southern China and Laos border northwestern to the central part of the country. The border area is steep and mountainous, with an average altitude of more than 2000 m. The mountainous region has a tropical monsoon climate and is influenced by northeast trade winds and typhoons. It receives a large amount of precipitation during the rainy season, with the annual rainfall reaching 4000 mm in some areas. From the Annan Mountains, the backbone of the Indochina Peninsula, to China in the north and west to Myanmar, the geology of the Mesozoic to Paleozoic Erases is widely distributed. The Paleozoic zone suffers from large-scale fold deformation (Nam 1995). Many ethnic groups live in these mountainous areas of Vietnam. Ethnic minorities generally retain their traditional lifestyles, and many make their living by farming in mountainous areas. While income levels appear typically low, the survey sites often provide glimpses of self-sufficient living styles. Survey

# The Author(s) 2023

N. K. Thanh (✉)

I. Alcántara-Ayala et al. (eds.), Progress in Landslide Research and Technology, Volume 2 Issue 1, 2023, Progress in Landslide Research and Technology, https://doi.org/10.1007/978-3-031-39012-8\_12

sites indicate that basic infrastructure, such as roads and electric power, are often inadequately developed, and the living and working conditions are poor.

In recent years, there has been concern that natural disasters caused by global warming and climate change are becoming increasingly severe, associated with heavy rainfalls, particularly in mountainous areas of Vietnam (MONRE 2021). The study areas have a long geological history of folding and faults. Moreover, chemical weathering during tropical rain has strongly affected the areas.

According to data on the risk of global disaster fatalities compiled by UNDRR (2009), South and Southeast Asia, from India and Nepal to the Philippines and Indonesia, are considered the world's largest high-risk regions.

#### 2 Regional Overview and Vietnam's Disaster Prevention System

#### 2.1 Slope Disaster Risk in Northwestern Vietnam's Mountain Region

A sizable tectonic region (Red River Fault) runs from northwest to southeast through the central part, along which flows the Red River. The area has elevations over 1000 m above sea level, containing Phan Xi Pang (3143 m above sea level), Vietnam's highest peak, which rises on the border of Lao Cai Province and Lai Chau Province. In these mountainous areas, unstable slopes are widespread, with active sediment movement associated with landslides and debris flows. There were 946 landslides in 15 northern provinces between 2001 and 2019, according to the Ministry of Agriculture and Rural Development (MARD) (2020). There have been 590 flash floods. These disasters resulted in the deaths of 748 residents and damaged 52,000 homes. One of the most striking aspects is that nearly 4000 houses were relocated due to the disasters.

In our preliminary survey, we noted that the mass relocation in villages was an early sign of the occurrence of landslides. Although relocations were in progress in other villages, some families reportedly returned to their old homes. Residents of North Vietnam are generally well aware of the high risk posed by landslides due to the prevalence of factors such as topography, geology, and climate conditions. It can be inferred that such awareness was a driving force behind the Vietnamese government-sponsored relocation program.

#### 2.2 Disaster Risk Characteristics from the Humanities and Living Environment Perspectives

The area around the northern mountain provinces serves as the residence of various hill minorities. Although the life and land use tendencies of each ethnic group are diverse, the Thai, Tay, Hmong, and Dao tribes have a population greater than 1 million (Dang 2002). Generally, they make a living by cultivating rice terraces on the slopes, paddy fields, and pastoring buffaloes. Rice terraces are an excellent way to use the landscape in this area, but this requires that the natural forests be cut down. Thus, there are concerns that the risk of slope collapses and debris flows will increase during heavy rains. We believe it is necessary to understand the relationship between the risk of slope disaster occurrences and land use. However, quantitative assessments of the relationship between the two have not been examined.

#### 2.3 Vietnamese Government's Disaster Risk Reduction Policy and Regional Disaster Risk Reduction Policy Initiatives and Challenges

Efforts to tackle slope disasters in Vietnam began with the enactment of the Disaster Prevention Law (Vietnam's National Assembly 2013). Tachi, a JICA expert from the Ministry of Agriculture and Rural Development (MARD), and Sakai, a JICA expert from the National Research Institute, took further steps (Tachi and Sakai 2019). Based on these references, we submitted a proposal for a slope project outlined by Disaster Risk Reduction. We will outline slope disaster prevention in particular.

Government Policy The Disaster Prevention Law sets out five basic principles for preventing and managing natural disasters. These are: (1) In extreme weather, the Vietnamese government must make proactive plans for the prevention and timely response to take prompt and effective corrective measures. (2) The prevention and control of natural disasters is the responsibility of the State, organizations, and individuals. The State plays a leading role, organizations, and individuals take the initiative, and local communities help each other. The prevention and control of natural disasters are carried out according to four maxims on the spot: command the local army for the organization of households or individuals in an area at risk of the natural disaster/s, vehicles and materials, and onsite logistics. (3) Natural disaster prevention and management content should be integrated into national and local socio-economic development master plans. Sectoral development master plans must ensure humanity, fairness, transparency, and gender equality. (4) For to prevent and control natural disasters, actions taken by the State must be based on science. Combine traditional experiences with the progress made through science and technology. A combination of structural and nonstructural solutions; environmental protection, ecosystems, and adaptation to climate change. (5) Prevention and control of natural disasters will be decentralized with close

Fig. 1 Diagram shows the relationship between slope disasters, objects, and management tools. (a) Management level pyramid from National to community. (b) Disaster management tools

coordination between armed forces and natural disaster risk levels (National Assembly of Vietnam 2013). An organizational chart of disaster prevention measures to be constructed at the local people's committees level is also presented. It clearly states that this mechanism assists with disaster prevention through the cooperation of each organization in the region.

Needless to say, natural disasters in Vietnam may also be related to social factors. In Southeast Asia, such as Vietnam, paddy field cultivation and slash-and-burn cultivation using slopes have been practiced since ancient times. This practice suggests that many people live on mountainous slopes, with a high possibility of landslide disasters and soil erosion due to land use. In a social environment where mountain slopes are both a place of land use and a residence, it suggests the necessity of measures to mitigate disasters (Fig. 1).

Especially in areas with moist tropical mountains, such as Vietnam, slope disasters are repeatedly disrupting the lives of residents. However, residents in mountainous areas lack the practical knowledge and skills to avoid disasters. Although government officials are concerned about this, adequate measures are not easy to take. Disaster prevention organizations are established at all levels, from the center to the local level, including the provincial, district, and communal levels. The ability to understand landslides at the actual administrative level varies from program to program, plan, or project. At the regional level, and in villages, it is necessary to formulate appropriate response plans, taking into account the level of knowledge related to individuals involved the disaster prevention.

We need to educate the residents to raise awareness of landslides, such as what they are, what their causes are, when they occur, and pointing out landslides and safe locations. Maintaining a map with appropriate accuracy will be necessary to satisfy the above requirements. Examples include (1) an integrated map of landslide risk assessment, (2) a landslide distribution map at an appropriate scale, and (3) a map that can help locals identify the extent of the landslide area and the features associated with the topography in the area in which they reside.

At the national level, the Ministry of Natural Resources and the Environment has prepared a slope-disaster risk assessment map at a scale of 1:50,000 for use in community-scale development (Hung et al. 2017). However, this is not easy to apply to the scale of local communities such as communes and houses. For their benefit, further creation of applicable disaster prevention maps is required.

#### 3 Significance and Framework of the Project Outline and Aim of the Technical Support Project

#### 3.1 Background to Building Relations and Identifying Issues Between Vietnam and Japan

In the past, the project "Development of Landslide Risk Assessment Technology along Transport Arteries in Vietnam" (Project leader: Kyoji Sassa, Academic Representative of the International Consortium on Landslide, ICL) was implemented as a project of the joint JICA/JST Planning Project (SATREPS) between 2011 and 2016 (Tien et al. 2017). As part of this project, "Extraction of Landslide Danger Slopes by Wide-Area Landslide Mapping" was established, and the authors of this paper (Miyagi, Hamasaki, DV. Tien, N.K. Thanh, etc.) are core members, leading to the cultivation of important technology, knowledge, and relationships. These elements proved to be foundational to the subsequent project. In 2017–2018, a science program was adopted as one of the JST's Sakura Science Programs, which allowed the authors to invite young engineers from Vietnam to introduce the current situation of landslide disasters and response measures in various parts of Japan. In 2018, an international symposium entitled "The Reality of Slope Disasters Caused by Earthquakes and Ways to Overcome Them" was held in Kurihara City. This event commemorated the tenth anniversary of the Iwate Miyagi Inland Earthquake, which caused the largest known landslide in Japan, the Aratozawa Landslide. Five years later, the Kurikoma Geopark was established in the wake of the landslide disaster. Kurihara City was the proposed municipality for this project but has had a history of academic exchange between Japan and Vietnam since 2011.

This project is implemented as JICA's grassroots technical cooperation. The project is organized into two parts. The Japanese side consists of Kurihara City as the implementing body of the proposed municipality and Advantechnology Co., Ltd., and the Vietnamese counterpart Department of Agriculture Rural and Development (DARD) of Lao Cai Province. ITST of the Ministry of Transport (MOT) is a support organization.

In 2015, the Third United Nations World Conference on Disaster Risk Reduction was held in Sendai. Here, the natural disaster response policy from 2015 to 2030 was adopted as the Sendai Framework for Disaster Risk Reduction 2015–2030 (UNDRR 2015). In 2015, the Third United Nations World Conference on Disaster Risk Reduction was held in Sendai. The natural disaster response policy from 2015 to 2030 was adopted as the Sendai Framework for Disaster Risk Reduction 2015–2030 (UNDRR 2015). Four of the seven action guidelines presented in the Sendai Framework focused on communities and residents relating to establishing early warning measures.

#### 3.2 Outline of Technical Support Project

Based on the background described above, this project aims to expand the experience and mitigation technology in Vietnam (cultivated over more than ten years) to the residential areas of hill tribes, which are considered to be one of the most challenging areas to reach and yet the most in need of such assistance. The intention is stated in the project title, "Capacity Building of local Community for Slope Disaster Risk Reduction - SLOPE DRR."

The overall goal of this project is for residents to work together to grasp disaster risks better and build disasterresilient communities. The immediate goal is for residents to take the lead in formulating and implementing disaster prevention, mitigation, and evacuation plans. To that end, (1) It will be necessary to grasp the characteristics and disaster risks in the community areas. (2) On the Japanese side, administrative authorities and regional disaster prevention officials will work together to implement an awareness program focused on understanding disaster risks and evacuation. (3) Community-level organizations will formulate evacuation plans autonomously based on the materials and experience cultivated in (1) and (2). (4) Through pioneering activities, we will foster disaster avoidance capabilities in local communities. As already stated, it is challenging to establish regional disaster prevention works in which residents take the lead. However, it is also true that in recent years, the development of various notable technologies and social systems in sensing has progressed. We are consciously utilizing UAV, AW3D data, and Google Earth. In this project, as a mechanism to foster a common understanding between engineers and residents through visualization and exchange of opinions, we are using technologies such as UAVs that can easily acquire images of the region at a low cost to construct precise maps using digital information through research. With the help of UAV-related technology, it is possible to assess a site with residents immediately after a disaster. This approach may have been different in conventional disaster research and disaster prevention planning. Residents can be victims of a disaster, in essence. We feel that the use of UAVs has the potential to foster collaboration among these individuals. In addition, using AW3D can pave the way for the region and the government to understand the disaster potential by developing regional topographic landslide distribution maps. Data can be created on digital topographic maps of wide areas that can supply much useful information regarding geography and geomorphology at a much lower cost than aerial photographs and the like. The AW3D JAXA/RESTEC/NTT DATA uses four million photos acquired by the Japanese satellite Daichi. This developed technology can build Digital Surface Model (DSM) data with a 2.5 ~ 5 m resolution anywhere in the world.

In parallel with developing high-precision local land information using advanced technologies, we will conduct a questionnaire survey of residents. Although the questionnaire is simple in terms of disasters and the necessity of disaster prevention, it will be possible to grasp the level of awareness of the residents themselves and the necessity of preparing basic materials for disaster prevention in the region. Some specific questions include: (1) To what extent do you grasp the status of disasters occurring in the region? (2) How much basic knowledge do you have about disasters in general? (3) How strong is the awareness of promoting regional disaster prevention? We believe that combining the local land information and the survey results will lead to constructing a technical and organizational system that contributes to regional disaster prevention.

In this project, three communes of two districts of Sapa and Baxat Districts in Lao Cai Province have been selected as pilot communes. In these areas, we collaborate with residents and the local government to promote initiatives that contribute to mapping, regional surveys, disaster avoidance, etc. In the following section, we report on the status of initiatives in Trung Chai Commune, Sapa District, Lao Cai Province, where progress is clear at this time.

#### 4 Various Initiatives for Mapping in Trung Chai Commune, Lao Cai Province

#### 4.1 Hypothesis of Communication Base Evacuation/Risk Mapping

Main Premise The importance and difficulty of regional disaster prevention is the development of an evacuation map among community residents. Disaster mitigation must formulate a disaster response map that balances disaster risk and regional safety and has been improved over and over for decades in Japan. This need is also clearly stated in the Natural Disaster Prevention Law enacted in Vietnam in 2013 (Vietnam Government 2013). The Red Dao ethnic group resides in the pilot area of the Trung Chai commune. According to interviews conducted in this study, their awareness of disaster prevention is very high (detailed interview survey in Sect. 4.5 in this paper). This study focuses on the

necessity and possibility of creating a "communication-based evacuation map to realize slope disaster prevention."

Two hypotheses have been established, as explained in the following two sections. We propose to select three local communities to serve as pilot communes. The goal is to create a more disaster-resilient commune by developing disaster prevention measures through interactive evacuation maps. Why is it necessary to "conduct two-way communication between engineers and residents and jointly create disaster prevention and evacuation maps" mentioned above?

#### Hypothesis 1: Using hazard maps can reduce disasters.

In reality, hazard maps are not currently utilized by residents. There are four main reasons for the lack of utilization of such maps, the first being that residents feel there is no prospect of a disaster. Every time a disaster occurs, a common sentiment from victims is that they never thought it would happen to them. This mentality is based on their assumption that since they were not affected by previous disasters, they will remain unharmed. The second reason is that residents do not put forth the effort to use hazard maps. If a person knew to read such maps, disaster response would be fast. Another reason hazard maps are not implemented is that the responsibility is often left to a government entity. Lastly, it's hard to predict how and where a disaster will occur, leaving evacuation maps obsolete. To summarize, reasons for hazard maps to be effectively useless are low awareness, shifting of the responsibility of implementation, the unpredictability of disasters, and a general sense of apathy.

Incompleteness Among the Hazard Map Maker A Hazard Map Maker wants to make an advanced map. It is developed with this specific use in mind. Hazard maps are often created mainly through contracts between the government and the contractor. Inevitably, the map is made considering the administration's thinking and budget. On the other hand, the target areas have extremely individual circumstances leaving a wide range of aspects for which the disaster prevention maps created are difficult for residents to utilize.

#### Hypothesis 2: If you make it yourself, you want to use it daily.

In general, residents have a vague sense of uneasiness about the possibility of disasters in the area, whether they make a map or not. With the following factors in mind, communities can use hazard maps: (1) Give subjectivity to maps created. (2) Since the community makes this map, it is more personal and will accommodate their interests and needs. (3) Learn from examples of disasters in surrounding areas, and use that to inform how to avoid similar problems, and evacuate effectively. (4) In addition to disaster prevention, it can also be used to understand the regions' characteristics.

Past Examples and Cartographers' Perspectives The above hypothesis is based on one of the authors' experiences with the effects of tsunami evacuation plans during the Great East Japan Earthquake in 2011 (Miyagi 2016). Since 2006, the author has been engaged in initiatives to evacuate residents in the event of a tsunami in some areas of Miyagi Prefecture in Japan. The region had already anticipated a significant earthquake and tsunami during the short earthquake. To this end, we have been conducting evacuationrelated field checks and making maps. This work was carried out so that "the authors and residents exchanged opinions" (Miyagi 2016). The region's conditions, related knowledge, and information change over time. For this reason, updating the map almost every year was necessary. There were two ways to create maps: My Evacuation Map for family members to evacuate and Community Evacuation Map to manage the area. Three months after the sixth upgrade was made and the version distributed to all households, the M.9.0 East Japan Earthquake occurred, and a massive tsunami with a maximum wave height of 10 m struck the area. It was on a scale far beyond expectations.

As soon as the earthquake struck, most residents fled to evacuation sites according to plan. However, we realized that the evacuation site could not be safe. Based on the mutual agreement of the evacuees, we made a second evacuation to a higher place. As a result, the number of victims in the community that had previously prepared evacuation maps was overwhelmingly small compared to others.

Here, we realized the greatest role of hazard maps. The residents learned the importance of cultivating disaster response skills through map-making. A resident said, "The tsunami did not come as you said. But I was studying, so I was saved by the second evacuation." To summarize this experience, the authors set the concept of cartography as follows.

#### "Communication Base Evacuation Mapping (CBEM)".

Integration of hypotheses: The two hypotheses above suggest that a hazard map will more likely be used when residents make it voluntarily.

#### 4.2 Mapping Steps

We have been working on mapping actual information in three communities to create a two-way slope disaster prevention map as a Communication Base Evacuation Map (CBEM) and figure out how to utilize it effectively. The steps for this map are as follows:

The above steps will be implemented for each community. By repeating these four steps, the disaster prevention capabilities of the region will gradually improve.

The target area belongs to an ethnic minority called the Red Dao. Since these people have distinct characteristics peculiar to the region (Dang 2002), discretion is necessary. As assumed here, the Dao people in the mountainous areas surveyed have yet to see an accurate map. Part of them may not speak Vietnamese. The illiteracy rate also seems to be high. On the other hand, many locals have recently mastered using smartphones despite many difficulties. With a smartphone, they can use open-source images like Google Earth. The current situation allows us to feel that there is a potential to dispel many of the concerns mentioned at the beginning of this article.

#### 4.3 Disaster Experiences of Residents

According to statistics for the past ten years (2010 to 2020) in Lao Cai Province (Table 1), many damage cases have been recorded, including 128 deaths and missing persons, 179 injuries, and damages to 3464 houses. As shown in Table 2, 103 people were recorded dead or missing in the flash flood in 2008.

There are 13 provinces in the northern mountainous region, not limited to Lao Cai Province. In addition, various slope disasters and flood damage occur in the mountainous provinces of central China almost every year (Lao Cai DARD 2021).

Case Study of Slope Disaster at Trung Chai Commune The commune is located halfway between Lao Cai City and Sapa City. The Mong Sen River flows south of the area and is paralleled by National Road 4D. The construction of expressways is currently ongoing. The Mong Sen area can be cited as a major landslide-disaster-prone area (Fig. 2). Landslides have been recorded in the Mong Sen region during heavy rains in 1998, 2002, and 2004. On May 9, 2004, a series of disasters occurred, including a largescale landslide near the Mong Sen Bridge, frequent debris flow throughout the surrounding area, and large-scale debris flows blocking the Mong Sen River (Yem et al. 2006; Duan

Table 2 Major natural disasters and the damage from 2008 to 2020 in Lao Cai Province, Vietnam (Lao Cai DARD 2021)

et al. 2011). In the region, surface landslides and debris flows have repeatedly occurred. Our visits confirmed micro features of secondary landslide deformation in Posingai and Mong Sen villages, which are part of a significant landslide topography. Many residents seem to have a grasp of where these disasters are located and the signs of disasters. They were also confirmed in a joint survey conducted by Vietnamese and Japanese engineers and residents, as shown in Fig. 6.

#### 4.4 Difficulty of Community Disaster Prevention

The provincial disaster prevention authorities (Lao Cai DARD), in charge of regional disaster risk management, have faced various difficulties unique to the field. According to the impression of community-level disaster prevention officers, efforts at disaster risk reduction on the community level seem to face various difficulties (Fig. 3). Specifically, more concrete measures are needed to improve the capabilities of people in charge of disaster management in a community. Experience in assessing disaster risks, the response to the risks, examples of what it means to have expertise in disaster management, and improvements to the abilities of the personnel in charge can occur immediately. Vietnam's community disaster prevention policy was recently launched (Vietnam's National Assembly 2013). However, organized guidelines on the importance and purpose of reducing disaster risks through the voluntary actions of residents and specific means have yet to be developed.

Each region is unique, with diverse disaster characteristics, infrastructure, and land use. Even if a national government or other super-authority sets uniform guidelines, it will be accompanied by difficulties applying them to the region mechanically. Furthermore, in the Vietnamese general society, the custom of using maps as essential information to accurately grasp the region seems limited. In addition, there are difficulties, such as not speaking Vietnamese and having a high illiteracy rate among ethnic minorities.

To summarize, the following five points should be improved. (1) Poor systematic knowledge of the disaster itself. Disaster prevention personnel at the regional level need to be equipped with the skills to assess the disasters experienced by the region and to examine the disaster

Fig. 2 Landslide and debris flow at Mong Sen Bridge, SaPa district Lao Cai in September 2004 (Left, Yem et al. 2006); Recent Mong Sen Aeras (Right, Thanh N.K., on March first, 2020)

Fig. 3 Difficulties in disaster prevention at the community level

prevention measures. (2) More concrete disaster prevention and disaster prevention scenarios must be implemented. Specifically, more than precipitation information that is thought to lead to the prediction of disasters is required. (3) Insufficient development of voluntary disaster prevention organizations has occurred. Organizations to tackle disaster prevention and mitigation are being developed in the region. However, the role that the members of these organizations should play needs to be clarified. In addition, the development of voluntary disaster prevention organizations with on-site response capabilities to address the issues in the individual local communities is an issue for the future. (4) More human resources are necessary. Both community and planning personnel are few. The number of trained people is further limited. (5) Extreme weather and disaster forecasting in recent years have been complex. The complexity of these projections makes the previous four efforts difficult.

#### 4.5 Interview Survey on the Necessity of Slope DRR

Characteristics of Residents in the Pilot Interview The interviews were conducted in Posingai Village in Trung Chai Commune and Lao Vang Village in Phin Ngan Commune, where the risk of landslide disasters is high. The inhabitants of the villages are ethnic minorities known as the "Red Dao." They have a history of seeing natural disasters that occur in their region in a day in 2016. After several days of heavy rains, the risk of landslides and debris flows increased, they thought. In light of this situation, the residents decided to relocate to an upstream land about 1 km away. In cooperation with the local government, they moved and settled there. Residents and the local government worked together to develop various infrastructures such as the maintenance road, schools, cultural facilities, and electrical machinery. However, to maintain their daily routines, they have to continue using their original farming fields, which are susceptible to landslides and debris flows.

Perception of the Current State of Slope DRR in Local Communities Local Communities: The interview was intended to increase the local people's awareness about slope disasters' impacts. This interview is believed to be a pivotal component of the direct approach to preventing slope disasters. Here, direct sensing is a technology that visually interprets land information acquired through a sensing tool. A typical example of this is aerial photo interpretation. In particular, UAVs can engage residents in work processes such as data acquisition, imaging, and three-dimensional processing. The data and interpretation results obtained in this process are expected to be independent natural sources for a common understanding. We can consider the significance of visual interpretation together with residents as highly significant. The UAV initiative is an attempt based on our hypothesis that the situation in which the residents are involved in the creation of materials will be directly linked to the revitalization of the use of data. From there, we can make an image from which it is feasible to evaluate the challenges to overcome in the short and long term and examine the feasibility of building a society that understands the most appropriate response solutions.

This study has five to six questions about the basic knowledge of slope disasters, involvement with local communities, and experience with disasters. These questions and the result are summarized in Tables 3 and 4.

Table 3 Results of the interview study related to the basic knowledge of slope disasters in the Trung Chai Commune and Phin Ngan Commune, Lao Cai Province, Vietnam

The response from the residents in the surveys indicated a need to reduce the risk of landslide disasters. They are often direct victims of disasters. In recent years, slope disasters have occurred frequently in the pilot area from 2016 to 2020, and large-scale slope disasters occurred in 2002 and 2004. Experience history proves that disaster prevention measures alone cannot protect the local communities and people's lives. Therefore, residents must formulate voluntary disaster mitigation measures to reduce slope disasters. To realize the residents' understanding of regional disaster risks, we will build a communication-based disaster prevention map that residents and engineers jointly implement.

#### 4.6 Arrangement of the Base Maps and Validity

Data Mapping in Trung Chai Commune (AW3D and Layer Structure Contour lines generated from the AW3D 2.5 m DSM data covering the Trung Chai area can be used to understand the primary land conditions of the area. In addition, land cover, roads, and building system information could be obtained from Google Earth. This information can be superimposed on AW3D maps by simple orthoprocessing (Figs. 4, 5, 6, and 7). This data will be the basis for creating a communication-based evacuation map

Table 4 Result of the interview study related to residents' basic knowledge of the community in the Trung Chai Commune and Phin Ngan Commune, Lao Cai Province, Vietnam

Note: Ans: is the answer, yes or no; RF is a rating based on votes; % is the percentage of answer votes

Fig. 4 Series of maps of a portion of the Trung Chai Commune, Lao Cai Province, Vietnam. Based on the 2.5 m DSM, and 5 m DSM from AW3D (ALOS World 3 Digital Data: created by JAXA, RESTEC, and NTT Data). (1) Contour map at a 10 m interval. (2) Ortho-image for the section in 1. Houses, colonies, and roads are overlain to direct identify within the image. (3) Slope angle classification map created by GIS. Landslide topographic area developing the slope angle primarily

between 15° and 35°. Surface failure primarily developed on 25° to 40° slopes. (4) Main scarp and the body of the landslide topographic area are marked based on visual identification. The debris flow and slope failure are also marked in blue as identified from the ortho and Google Earth images. (5) Ridge system and stream network system identified by the contour patterns. (6) Overlapping of the slope disaster results on the contour map

Fig. 5 Variety of the autochthonous rock facies compared with landslide materials at Trung Chai Commune, Lao Cai Province, Vietnam. (1) Fresh rock identified as "Granitic gneiss." (2) Fresh hard rock facies

(CBRM) that can be edited to be easy for local people to use. It is also necessary for the residents to understand the engineers' intentions to prevent regional disasters.

To put it simply, as mentioned previously, no matter how precise a map for disaster response is created and provided, it will only be meaningful if the residents can understand and use it. More is needed to provide and visualize information. Instead, engineers will also need to deepen their understanding of the region through the exchange of opinion and be required to have the flexibility to make corrections for a more user-friendly map.

### 4.7 Verification of the Landslide Topographic Area Distribution Maps

In this research, contour lines are formed from AW3D DSM data acquired with a grid size of 2.5 m to 5 m as primary data

exposed at channel and waterfall. (3) Slightly weathered rock with joint systems. (4) Deeply weathered rock mostly changed to a clayey texture with an identifiable grain pattern structure

for the mapping, including the landslide topography. Therefore, the accuracy of the terrain information is controlled by the grid size of the data. Also, since it is a DSM, it does not reproduce the terrain but often reproduces the surface of the vegetation cover layers. It seems unreasonable to use this as a source for topographic classification. However, if the contour line data generated from DSM is observed based on its accuracy, it is possible to grasp the topographic characteristics. From this viewpoint, reading the pattern of contour lines does not make any difference from conventional aerial photo interpretation. From the generated contour lines, it is not possible to grasp small-scale terrain features such as surface failures. On the other hand, it is possible to decipher the morphological characteristics of large-scale landslide phenomena on a spatial scale exceeding several hectares.

AW3D data is used as the source material to grasp the disaster risk in the area to prepare the landslide topographic

Fig. 6 Field evidence based on the collaborative investigation with community residents at Trung Chai Commune, Lao Cai Province, Vietnam. (1) Recent overview of the Mong Seng Landslide (Taken on 28th Feb. 2022). The same landslide was mentioned in Fig. 2. (2): Vertical dislocation observed (between the two arrows) one year ago by the resident. It is located at the top of Mong Sen Landslide. (3) The large crack stretching near the step (No. 6) that is getting wider annually. We suggest placing a marker set. (4) Exposed huge boulder and accumulated at the landslide body. (5, 6, 7, 8, and 9) There are apparent

distribution map. At the same time, we used high-resolution image information such as ortho and Google Earth images to identify superficial and small-scale disaster phenomena such differences between landslide materials and bedrock. The landslide body consists of deeply weathered clayey soil and crushed angular to subrounded gravel. Huge boulders are also present. (10) The slip surface of a part of the landslide material. The surface is about 7 cm thick and consists of clay to sandy loam with a thin foliated structure. (11) Buried wood fragments under the slip surface (No. 10) subject to C-14 dating in a laboratory. 12: A large wood stem (4 m long, 30 cm in width) is exposed nearby the images in No. 10 and 11

as surface slope failure and debris flow. The disaster risk is obtained by superimposing both pieces of information in a particular area.

Fig. 7 Landslide topography and the field evidence collection sites at Trung Chai commune

There is a slight gap in the understanding of slope disasters between the authors and the administrative authorities. It is necessary to devise ways to reconcile this understanding. Tachi and Sakai (2019) highlighted the following regarding recognizing slope disasters in Vietnam. Vietnam's Disaster Prevention Law (2013) defines slope disasters differently from Japan. Two categories of landslides and debris flows are defined in the broad classification. "Landslides" are a combination of landslide topography and surface landslides, as depicted in this paper. On the other hand, "debris flows" collectively cover everything from surface landslides to debris flows. It is unrealistic for large-scale phenomena like landslides to be categorized together with surface landslides. In addition, categorizing debris flows and surface landslides together as debris flows is also very different from the classification used in Japan and is controversial.

Field Evidence and Mapping Validity In this research, a distribution map of landslide topography is created using only contour information. Landslide topographic distribution maps have traditionally been created by interpreting aerial photographs. From aerial photographs, it is possible to decipher the morphological characteristics and related information such as vegetation, land use, small steps, and cracks in the ground. Aerial photo interpretation engineers have also considered this relevant information to determine the landslide terrain area. Based on this point, it was judged that when mapping using only contour lines, it would be necessary to evaluate the validity of the interpretation results through confirmation through field surveys.

We clarify the validity of landslide topographic mapping. In general, it is known that variations in landslide properties produce several characteristic shapes and material structures. Among these characteristics, the geology of the landslides, the microtopography, the sediment characteristics of the landslide body, etc., were confirmed. At the same time, on-site interviews were also conducted (Fig. 6).

Geology The study area comprises granite gneiss of the Ordovician period of the Paleozoic Era. However, the study site is located in the humid tropics, suffers strong chemical weathering, and is expected to have significant weathering and viscous soiling. The stratigraphic phase of sediments disturbed by landslide action may be similar to that of weathered rocks. Here, to distinguish the determination of landslides from the rocks, the characteristics of the rocks were confirmed in the rock phase series from fresh rocks to strongly weathered rocks (Fig. 5). Even weathered primordial rocks often show crystalline particle structure and quartz veins. Using this as a clue, we checked to see if a landslide was deforming the mapped area.

Landslide Body Properties The landslide body that constitutes the area for the landslide terrain differs from the rock phase of the original position described above and is composed of disturbed and crushed sediment (Figs. 6, 7, 8, 9). In rare cases, the slip surface and typical landslide sediments can also be confirmed (Figs. 6, 7, 8, 9, 10). Even today, it fluctuates slowly, and buried wood was found in the mobile body of the landslide when anchoring was installed (Figs. 6, 7, 8, 9, 10, 11, 12). The Japan Accelerator Measurement Laboratory collected and commissioned a portion of this to the C-14 date using the AMS method. An age of IAAA-212510 40,204;/-284 cal. BP. (Calendar year correction) was obtained. In addition, huge boulders with diameters exceeding several meters in many landslide areas are also noteworthy (Fig. 6). In landslide movement, thick, fragile, viscous weathered soil layers also cause fluctuations in fresh rocks and deeply weathered core stones during landslides. Megaliths that are resistant to surface erosion are selectively left.

Microtopography Indicating Landslide Variation Steep horseshoe-shaped slopes dominate typical landslide terrain through a distinct slope transformation line with the Fig. 8 The simple mapping with UAV data (All data has been reported by Thanh et al. 2021)

surrounding non-landslide slopes. This forward-expanding mobile body forms a gentle slope. If such a topographic composition can be observed at the site, it can be judged as a landslide terrain. In addition, if a small deformation such as a step or a crack can be confirmed in part of the terrain, and the deformation is harmonious with the assumed change in landslide movement, it can be judged as a sign of a landslide (Figs. 3 and 6).

Resident Information Red Dao, whose residents live in the area, has been cultivating paddy fields for hundreds of years. The landscape of the rice terraces has cultural and tourist value. The residents have agreed to an evident division of land ownership, and once landslide features develop, they work together to address them. Therefore, the landslide movement might be remembered for several decades. For example, the Monsen landslide introduced earlier seems to have repeatedly been moving over the past few decades (Fig. 6).

Figure 7 shows the distribution of landslide topography drawn through contour interpretation, overlaid with evidence of landslide variation confirmed at the site. The distribution map of the landslide terrain drawn from the contour lines and the confirmation at the site are generally harmonious.

#### 4.8 UAV Data Collection Study for Site Map and the Validity at Trung Chai Commune

#### 4.8.1 Overview of UAV Data Acquisition and Mapping

Many image data sets were acquired using UAV and converted into a three-dimensional digital information model using SfM's technique, resulting in multi-viewpoint photogrammetry. From image acquisition to generation and analysis of contour information, we worked together with residents. This collaborative work will significantly deepen the residents' understanding of the map and give impetus to understanding disaster risks and formulating evacuation plans. The technology to visualize dimensionally is the Structure from motion (SfM) (Westby et al. 2012; Saito et al. 2018). This technology is used in various fields. Paradoxically, various small local changes can be captured by repeatedly acquiring images. At the same time, the operation skill of the UAVs will be deepened.

UAVs are capable of responding to the needs of smallscale study areas, especially within a limited budget, and are easy to use. These characteristics will be a powerful weapon to pave the way for the mitigation of slope disasters by understanding the living conditions of the residents in

Fig. 9 Landslide recognition using UAV data for Site A (Thanh et al. 2021)

Fig. 10 Landslide recognition using UAV data for Site B (Thanh et al. 2021)

Fig. 11 UAV Mapping at Site C (New Posingai Village) in March 2022 (by Thanh N.K)

tropical mountainous regions, expanding disaster prevention knowledge, and understanding disaster risk.

Data Collection and Mapping by UAV in Trung Chai Commune UAV data collection and detailed mapping have been carried out in Posingai Village, Trung Chai Commune, Sapa Town, Lao Cai Province. The first flight area of 3.6 square kilometers was flown in 2019 using DJI Phantom-4 Pro equipment. A series of photo images were analyzed automatically using Pix4D Mapper software with the output Ortho-mosaic images and DSMs. The simple map of this area is presented in Fig. 12. We worked with the

Fig. 12 Explain the Slope DRR and CBEM. (1) A Lao Cai DARD officer representative presents the significance of promoting community-based disaster risk reduction (Trung Chai Commune). (2) Explain the meaning and contents of this activity (Trung Chai Commune). (3) Discussion with the village leader at Posingai (Trung

Chai Commune). (4) Presentation of the significance (Thanh Binh Commune). (5) Luncheon meeting at the resident's house (Thanh Binh Commune). (6) Explanation of a mapping sample (Phin Ngan Commune)

residents to check and confirm the landslides and debris flows in the field. A topographic map with 5 m contours was built (Fig. 4). Landslide identification (Miyagi 2013; Hamasaki and Miyagi 2013a, 2013b) was implemented to identify and transfer an inventory map using the UAV data.

Within a 5 km long stretch of National Road No. 4 and its branch line running through the part of Posingai Village, 40 slope disasters were identified. They varied in size and type. Landslides, slope failures, debris flows, rockfalls, etc., could be identified. In addition, we also found places that showed unstable rocks.

From Fig. 12, we created a detailed site map for three places that we judged particularly noteworthy.

Site A (Monsen Landslide Site): A massive landslide hits Route 4 and has been plagued repeatedly for years.

Site B (formerly Posingai Village): Formerly the center of the village. In 2016, a large-scale debris flow occurred. In 2017, residents gave up on living in the area and relocated. Currently, only two households are in this area.

Site C (New Posingai Village Relocation Site): This is a new area for the relocation from Site B, where roads have been improved, and many houses have been relocated. This area is a district that expects to conduct evacuation drills.

This map shows the Mong Sen Area - a typical landslide with a width of 250 m and a height of 200 m. Referring to LS-MS 001, the slip surface depth is estimated to be about 10–20 m deep. The landslide body has been moved and changed into multiple landslide blocks. In pictures nos. 1, 2, 3, and 4, a field check was carried out, and the marked landslide sites were recorded in March 2022.

Figure 10 shows the details of site B, where in August 2016, a debris flow appeared on the natural slopes from the impact of typhoon No. 2. The initial appearance of gullies on the weathered granite surface of the natural slope is shown. The depth of the gullies is from 1 m to 3 m. According to the terrain's natural Slope, the gullies gradually expanded and gathered to form a fan shape. The main scarps of debris flows are visible on the ortho-mosaic, for example, at the LF 010 location.

Recent UAV data of Site C (New Posingai Village), in March 2022 It was foggy when we flew a UAV to shoot the area, a common feature in the Sapa Lao Cai, but we could finish the flight. Using just about 20 minutes of automatic flight at an altitude of 300 m over a flight area of 400 m by 400 m, UAV imaging data at the center of Posingai village was collected. The accuracy results from quick data analyses with an average ground sampling distance (GSD) equal to 11.1 cm/pixel were carried out shortly afterward. The contour map from DSM makes it easy to recognize the slope stability. The created DSM and ortho-mosaic resolution data are useful for situations that need data quickly, such as training local people to evacuate.

#### 5 Discussion of Map Adaptability and the Validity for Community-Level Slope DRR

#### 5.1 Community-Level Disaster Prevention and Evacuation Map

A map identifies a study area and appropriately visualizes the facts in that range. The purpose of this study is to use maps for community-level disaster prevention. The community can be broken down into several scales. In addition, each community is unique. The following viewpoints are set: (1) A map to help residents implement the evacuation plans appropriately, and (2) A map to visualize the area's characteristics, a place of daily use. To achieve these viewpoints, it was necessary to identify a suitable scale, the range to examine, and the methods of expression, among other factors. However, many different stakeholders are involved in a community-level disaster prevention program. There are several hierarchies, such as the ministry, which has jurisdiction over disaster prevention; the county, which oversees disaster prevention of the region; the commune, which will confront the disaster, the village, the home, and the individual. The contents represented on the maps should be decided with their needs in mind.

On the other hand, the cost of creation and technical difficulty should also be considered. In this study, the landslide map at a scale of 1/25,000 had already been developed. When the slope disaster danger at the province level and the county was depicted, an exchange of opinions was undertaken to find a suitable scale. The scale was agreed to be between 1/5000 and 1/10,000 for specific areas (ex., Trung Chai, Phin Ngan, and Thanh Binh Commune). A map of commune-level disaster management was also prepared. For these maps, we used 5 m DEM and 2.5 m DSM data from AW3D, which covers the entire world at a lower cost when compared with aerial photography. It may also target a specific village like Trung Chai and other communities. UAV data was taken and used for this section. The maps created by UAVs are named "Site maps." For concrete mapping, it is necessary to consider the purpose and means of the stakeholders' intentions. Here, we considered the ideal way for the appropriate maintenance of maps, mainly in Trung Chai Commune Posingai Village, where the most information was collected as an example.

#### 5.2 Case Study of Site Mapping at Posingai Village in Trung Chai Commune

Trung Chai Commune is a county with an area of about 30 km2 and consists of four villages. Therefore, we mapped about 25 km2 using the AW3D as the base map (Fig. 4). Although the evacuation plan of Posingai village was made in that, Posingai village is about one-third of the area of the mapped region. The densely populated area is a much smaller part of the map. The current main settlement of the village is located on more complex mountain slopes. There is a history that all houses were consulted several years ago and moved to a place that was assumed to be safer because signs of a landslide appeared in the old village. Specifically, dozens of houses were moved to an area with several narrow ridges and valleys in about 20 ha only.

Based on the two viewpoints outlined at the beginning of this section, we proposed an effective map communicating the evacuation plan for Posingai Village. Suppose a community-based disaster management map is to be produced on a village-by-village basis. In that case, it will be necessary to show the main portions of the village and the relevant adjacent areas in one figure. On the other hand, it is necessary to understand and visualize the situation in further detail, such as areas with the population scattered in the village and places with high disaster risk. With this in mind, a photographic map was prepared based on images taken with a UAV. In addition, we tried to express the slope characteristics and locations of villages, including those relocated on a three-dimensional map, to make it easier to understand.

In this paragraph, we discuss the effectiveness of UAV-based mapping. The site map data obtained by flying a UAV has significant advantages and some limitations. There are limits to the range of maps. Suppose the area over which data is acquired is large. In that case, it will take a considerably long time and technical skills in various points of the acquisition time, data processing, and representation as figures. It becomes complicated even if corresponding figures are created. As a result, it is extremely difficult for an end user, such as the residents, to understand the map. The UAV data is a point to map the necessary range. When the community realizes the necessity by themself, sometimes the resident and the engineer call the data collection and develop the map together.

The initial site maps (acquired in 2019), which were created for Posingai Village, are a brief indication of the regional conditions immediately after the disaster that occurred in 2016. The effectiveness of the site map is further increased by combining it with photographic evidence on site. In addition, we introduced the site map acquired in March 2022. It provided the state of the whole village three years after the site map was acquired. The Structure of the village has almost become clear. Based on this map, the villager exchanges opinions on selecting evacuation sites and routes during heavy rains. A site map can show the disaster risk and strengths of each house block in a village, with a tentative name like "Disaster strengths and weaknesses around us. With this map, it might be possible to maintain a medical record to prevent disasters in each house. Figure 17 shows a possible example.

As mentioned above, creating and presenting disaster prevention maps according to the actual regional conditions on multiple scales over different ranges with accuracy and periodic improvements with the assistance of residents will lead to improvements in the effectiveness of disaster prevention.

#### 5.3 Workshop for Creating the Communication Base Evacuation Map "CBEM"

To succeed in CBEM, a mutual understanding between the engineers and the residents is necessary. We already described the steps to develop a CBEM. Next, we will consider the actions that can be taken.

Explain the Slope DRR and CBEM As introduced, the Vietnamese government's policy promotes communitylevel disaster prevention. Therefore, the region carried out a series of activities described below. First, a person in charge of The Laocai Department of Agriculture and Rural Development (Laocai DARD) of the local government, which is the promotion base, will explain the purpose, set the goals, and points to emphasize for regional disaster prevention promotion to the management sector through the community officer. Next, we explain the importance of materializing CBEM and the associated creation procedure. The project has three pilot communes: Trung Chai, Thanh Binh, and Phin Ngan. We carried out the work in the same way in each commune, as shown in Fig. 16.

#### Initiate the Interest (Case study/Picture Story Show)

Residents need to understand the significance of disaster prevention and mapping to ensure that the effectiveness of community-level disaster prevention, primarily evacuation actions, can be guaranteed, as described earlier in this paper. Above all, the inhabitants of this area are ethnic minorities called the Dao people.

Various difficulties hamper community-level disaster prevention efforts. For example, in Vietnam, which is a multiethnic nation, mountain minorities do not necessarily understand Vietnamese. It is not necessarily understood that disaster prevention is accompanied by concrete action. In other words, there is currently a common sentiment that this topic is viewed and heard through public relations from the administrative authorities. However, as detailed in part 4.5, residents seem to believe that merely recognizing the need for disaster prevention is enough. Community-level disaster prevention begins when residents understand their significance and the specifics of disaster prevention and evacuation. If the

Fig. 13 Workshop communication, explaining the Slope DRR and CBEM in Trung Chai Commune. (1) Explain the outline of the base map and related Images in the commune. (2) Explain the enlarged base

map on the blackboard. (3) Group leader reports their recognition and their description to others. (4) Write while talking the knowledge through the engineer. (5, 6) Write through the advice

residents are conscious of the significance of implementing the specifics independently, the actual prevention and evacuation may be attained. Thus, it is naturally necessary to emphasize the importance of disaster prevention and evacuation and to arouse interest. We introduced the case of Japan as an approach to attention. Next, we performed a disasterprevention picture story show, "Kamishibai," based on the community characteristics of the Dao people.

Base Map Present and Workshop for Developing CBEM We explained the base maps developed using AW3D data for community-level disaster prevention management. These maps will become the materials for the foundation of CBEM. We also created a UAV-based site map. At the workshops, the district-disaster-prevention infrastructure map was introduced to the residents. Next, a map is distributed to each resident, and individual data, such as names, roads, residential zones, etc., are filled in. Through these processes, it was possible to make clear the community images and disaster risks among the residents. The maps were assumed to be the first experience for ethnic minorities in Vietnam to see detailed and systematic community-level maps. In addition, developing a map based on the actual understanding of the residents is an essential step to completing CBEM. Many community-level disaster prevention personnel and district residents participated in the workshops. There was no extreme bias in the age groups or genders of the participants. To widely grasp the ideal way of map understanding, which presents each district by changing the description items and the description range little by little, it was more rational for all stakeholders (Fig. 13).

#### 5.4 Data Analysis of the Spatial Cognition of the Residents

Results and Suggestions for Easy Use in the Community Through CBEM Creating a disaster prevention map that the residents want to use is essential for disaster risk management. We applied the method of making CBEM, which Miyagi (2016) successfully implemented in Japan, to the mountainous ethnic groups in Vietnam. In CBEM, a mutual understanding was the starting point for establishing a dialogue. As a result, CBEM proposed to create a map that clearly describes the main characteristics of the region, primarily using AW3D data. The important buildings related to the social environment, especially educational facilities, and life-related information are to be shown. They include the people's committee hall, school, hospital, and other social environments; topographical water system; disaster-related information such as landslide topography and debris flows; and life-related information such as roads and dwellings.

The Dao Ethnic Group area is too sparse to identify a specific location. The sphere of the daily life of the resident is limited to the village. Fellow villagers can identify the individuals and houses concerned. On the other hand, interest in neighboring villages was extremely scarce. It was realistic to prepare a regional disaster prevention management map based on this background. The above basic information was posted on the CBEM, but some blank items were always included in the legend for personal necessity. For adding the necessary information, the proposed regional disaster prevention management map had a column describing agreed-upon essential places in the region. They include

Fig. 14 UAV data of Posingai village Trung Chai Commune and 3D image extracted using ADCALC 3D

temporary evacuation sites, evacuation facilities, expected secondary evacuation routes, individual houses, and neighbors' homes with close relationships. By marking this while discussing with the family, the residents will be able to complete their own customized CBEM. On the other hand, more detailed map information was also required for the region.

The process of making the map called for the residents to use their experiences. To develop an easy-to-use map, it was necessary to include such information. The presentation of the photo map and the images from UAVs showing traces of past natural disasters was indispensable for regional understanding and disaster prevention. In addition, 3D information extracted from UAV photographs using Adcalc3D is also presented. Some actual residents, for example, routinely viewed open-source image data, such as Google Earth. Future developments in the residents' understanding of open-source image data are expected (Fig. 14).

#### 5.5 Discussion with the Residents for More Understanding of the Evacuation Drill Planning at Posingai Village, Trung Chai Commune

For the evacuation drill plans, maps usually have a suitable scale for the purpose. The mapping by AW3D was suitable the set up the general orientation of evaluation. UAV mapping was effective in direct and exact site imaging among the residents. These maps were suitable for identifying the exact locations. Residents need to recognize their homes on the series of maps.

Given our previous experiences at Posingai Village in 2021, when using UAV maps, the ability to see residents' houses and the surrounding features was much easier. With a trial UAV map, almost every resident could confirm the location of their home and nearby features along the evacuation route. A discussion on the evacuation drill plans at Posingai Village, Trung Chai Commune, was conducted in April 2022 between us and the experienced residents of the village, the former village chief, and reputable people in the community. The steps of the discussion process are shown in Figs. 15 and 17.

These figures showed the final result of the discussion. The five locations (A to E) in Fig. 16 were considered safer by the people. They decided on an evacuation shelter at a higher place deemed relatively stable. The remaining four locations are areas with high, smooth, and flat shapes and sufficiently stable to save each person. However, the areas risk isolation when debris flow and surface failure occur along the road.

Since the date and conditions at the occurrence of a disaster can not be selected, evacuation plans should be made for multiple conditions. For example, in the case of Posingai Village, the location of the inhabitants is completely different during the daytime versus the night. The presence of elderly, disabled family members, and pregnant women also change over time. It is also necessary to develop a new system to respond to such situations and promptly advance discussions on what conditions make this district the most

Fig. 15 UAV site map after discussion with the community residents at Site C: Posingai Village, Trung Chai Commune

vulnerable to disasters. We summarized the steps of the scenario of the evacuation drill in Fig. 17.

The most important things are evaluation meetings for the next. Assessment of safety after a landslide occurs through people's observations of the area's topography after the landslide. This assessment is the first step when discussing using maps and evacuation drills with residents.

#### 5.6 The Evacuation Drill at Posingai Village, Trung Chai Commune

The evacuation drill was carried out between the people of Posingai Village in Trung Chai Commune in June 2022 and us. With nearly 100 participants, five locations assessed as safe by residents were identified for evacuation drill purposes, as discussed in part 5.5. It was raining during the evacuation drill, which is a realistic simulation condition for when a natural disaster might occur. The evacuation drill is divided into two phases. The first phase is to get the locals used to the alarm signal. When the alarm sound is triggered, people move quickly from the village hall (point O) to the elementary school area (point A) in Fig. 18. The request is that people move quickly, support volunteer forces and the elderly, and leave heavy properties such as corn bags, rice bags, etc. As a result, three minutes were required to move all people to a safe location with a travel distance of 300 m.

The second phase of the evacuation drill is carried out when people are in their houses under the assumption that a slope disaster divides the residential areas. When the warning sounded, people from clusters of houses moved to five safe areas (A, B, C, D, and E) in Fig. 18. The head of each residential cluster was responsible for guiding people to move along the route defined on the maps. During the exercise, UAV was used to re-record the entire process. People were moved to safe areas within about five minutes.

#### 6 Remark: How about Realizing Autonomous Disaster Risk Reduction in the Community by Aiming for a Usable Slope Disaster Prevention Map?

To reduce slope disaster risks for ethnic groups living in mountainous provinces of northern Vietnam, we prepared maps and improved them through dialogues with local organizations trying to utilize their experiences for disaster risk reduction and evacuation drills. Three pilot communes in Lao Cai Province were designated, and the implementation status of the program was reported.

Fig. 16 Modified Village SLOPE DRR Management Map based on discussion with residents and engineer

Fig. 18 Evacuation Drill at Posingai Village, Trung Chai Commune, Laocai Province on June 2022

In the last decade, the progress of sensing tools and technology has been remarkable. In addition, the expansion of open-source images and GIS data has also been remarkable, along with discussions on the environment and disaster prevention. This project is aimed at the living areas of mountain minority ethnic groups that are generally considered to be far from investment in technology and limited in the budget to alleviate disasters. These groups live in poverty and remote areas where infrastructure development is still inadequate and traditional lifestyle habits are present. Because of this, we thought that utilizing the latest sensing, which is now considered easy, would open the way to free efforts in regional disaster prevention. Mountain minorities do not usually speak Vietnamese. However, most residents use a smartphone. Initially, we imagined that the project would be challenging. However, in actuality, we, the engineering side, and the residents understood each other the contour lines on the map as an image, and we understood the difference between a large-scale landslide and a surface landslide. In their daily life, the residents had a rough grasp of the topography, the local space, and the risk of disasters. The mapping of regional information is now easy to understand for residents. What was once considered difficult to read and

not worthwhile has now been organized into an easy-to-read map. Based on this experience, we may be able to reconsider the use of Communication Base Evacuation Mapping (CBEM).

Acknowledgments This paper is a reconstruction, addition, and correction of a part of the dissertation titled "Development of the Direct Sensing Technology for Slope Disaster Risk Reduction with the Special References of Local Community Management in the Humid Tropical Mountains, Vietnam" application submitted to Tohoku-Gakuin University in 2022 by the first author, Nguyen Kim Thanh.

#### References

Open Access This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/ licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

1 Note: Year of publication in Vietnam has been indicated with Asterisk.

# Landslide Risk Assessment in the Tropical Zone of Vietnam as a Contribution to the Mitigation of Natural Disaster Vulnerability

Dinh Van Tien, Nguyen Kim Thanh, Lam Huu Quang, Do Ngoc Ha, Kyoji Sassa, Toyohiko Miyagi, and Shinro Abe

#### Abstract

Landslide risk assessment is considered an important objective in minimizing damage caused by this extreme event. The biggest challenge of assessing landslide risk is predicting the likelihood of a catastrophic event. To evaluate this possibility, studies have focused on building integrated maps of assessment, using predictive models such as testings, scale models, numerical models, and actual field observations. This article summarizes the research achievements and applications achieved in the past ten years of the Institute of Transport Science and Technology in the landslide risk assessment in Vietnam.

#### Keywords

Landslide · Risk assessment · Potential · Susceptibility · Reactive · Testing · Ring shear apparatus · Monitoring · Early warning

Tohoku Gakuin University, Sendai, Japan

D. N. Ha VNU Vietnam Japan University, Hanoi, Vietnam e-mail<EMAIL_ADDRESS>
#### K. Sassa

International Consortium on Landslides, Kyoto, Japan

T. Miyagi Advantechnology Co., Ltd, Chiyoda, Japan e-mail<EMAIL_ADDRESS>
S. Abe Okuyama Boring Co., Ltd, Yokote, Japan

# The Author(s) 2023

#### 1 Introduction

Vietnam is located on the Indochinese peninsula in Southeast Asia, with a population of over 90 million people. The average annual rainfall from 1400 to 2400 mm receipt in most places of the country, with some places reaching over 4000 mm Vietnam regularly suffer from 7 to 10 tropical storms accompanied by floods and landslides. Over the past two decades, natural disasters in Vietnam have caused more than 13,000 casualties and over US\$6.4 billion in property damage, of which landslides are considered the most catastrophic natural disasters.

Vietnamese Government Strategy for landslide reduction to mountainous areas and central highlands is "proactively prevent natural disasters", for which landslide risk evaluation is one of the key solutions. The Institute of Transport Science and Transportation (ITST) under the MOT was established in 1956 as an institution for science and technology research and application for the transport sector. For more than 35 years ITST has been involved in the landslide field and proposed several solutions for scientific research and new technology application in disaster prevention, response, and mitigation to specific strategy mentioned above. Since the ODA Project named "Development of Landslide Risk Assessment Technology along Transport Arteries in Vietnam" began in November 2011, the development of new landslide risk assessment technology and its application to forecasting, monitoring, and disaster preparedness of landslides in Vietnam has been raised to a new level and contributed to geo-disaster reduction along main transport arteries and on residential areas. This paper is a summary of the achievements in Landslide Risk Assessment in the tropical zone of Vietnam that contributes to the mitigation of natural disaster vulnerability over the last 10 years.

D. Van Tien (✉) · L. H. Quang

Institute of Transport Science and Technology, Hanoi, Vietnam N. K. Thanh

Institute of Transport Science and Technology, Hanoi, Vietnam

I. Alcántara-Ayala et al. (eds.), Progress in Landslide Research and Technology, Volume 2 Issue 1, 2023, Progress in Landslide Research and Technology, https://doi.org/10.1007/978-3-031-39012-8\_13

#### 2 Concept of Landslide Risk Assessment

The term "risk" combines the concepts of threat to life, difficulty and danger of evacuating people and property in the event of a disaster, potential structural damage and house value housing, social disruption, crop loss, and destruction of public facilities.

In the framework of this paper, the concept of risk is determined from the point of view of the International Center for Geohazards (ICG) of the Norwegian Geotechnical Institute (Uzielli 2009) as follows: R = HxVxE (1) Where: R (Risk) is the possibility of loss due to the accident occurring. H (Hazard) is the likelihood of a catastrophic event occurring. The value of H will be determined between 0 and 1, where H = 0, corresponds to no events occurring, and H = 1 corresponds to certain events. H has no units. V (Vulnerability): When an accident occurs, injuries may be caused to people, their production, and daily life. V is understood as people's ability and material, social, economic, environmental, cultural, institutional, and political assets to be damaged due to disasters. V has no units and ranges from 0 to 1, where V = 0 corresponds to no injury and V = 1 corresponds to complete injury. E (Value of Vulnerable Elements): Vulnerable elements include people, assets (houses, traffic structures, vehicles, crops, livestock...), livelihood activities, and the environment. E is defined in monetary units (for economic damage assessments) or person units (for human damage assessments).

Along with the concept, risk assessment methods are also increasingly diverse. These methods can be grouped in two directions of assessment: direct—qualitative and indirect quantitative (through a set of indicators), specifically: sociological investigation method, integrated cartographic method, etc. combination and index method. Each assessment method has its advantages and disadvantages.

For the field of landslides, due to the diverse nature of scale, type, and large distribution space, when considering the concept of risk, most scientists focus on assessing the probability of occurrence of hazard event (H) on an area scale and evaluate the risk for specific landslides.

Assessing the overall landslide risk for an area involves answering the questions of what "types of landslides occur", "where they did occur", "where is landslide susceptibility area", and "how likely they are to reactivate". The best tool to assess landslide risk for an area is the development of integrated landslide maps related such as landslide distribution maps, landslide classification maps, landslide susceptibility assessment maps, or reactive assessments of landslides that have occurred. Based on integrated maps, the planning, land use, response, and damage reduction of the phenomenon are determined. Due to a large number of occurrences, the assessment of the probability of occurrence of each landslide in an area is usually not covered. However, risk assessment for the specific landslide case is mentioned for landslides with special significance such as large scale, important located places. Models for prediction at different levels such as laboratory tests, small-scale simulation models, numerical models, and monitoring and evaluation of characteristic parameters on Real models are used to study and evaluate the shifting mechanism through the expression of related parameters. Based on result predictions from these models, the mitigation measures are determined.

#### 3 Achievements in Landslide Risk Assessment

#### 3.1 Landslide Identification and Integrated Landslide Mapping

#### 3.1.1 Landslide Identification and Landslide Topographic Area Mapping

As mentioned above, the first input when assessing landslide risk is to recognize the type and location in which they are distributed. When a landslide occurs, it will change the topography of the area and leave easily recognizable and distinguishable signs on the land surface from the surrounding environment. Most of these signs are related to changes landform of the topography of the area. To identify the phenomenon of landslides, it is necessary to have a view from above and the surrounding area of the overall slope failure to identify the features and interpret the changing process of these features over time. In the recognition and interpretation of aeronautical images, a three-dimensional view of the deformation of a slope can be established through stereoscopic observations of pairs of aerial images for aeronautical interpretation. Through this stereoscopic image, an overall picture of the land can be observed; Landform classification, land cover classification, and vegetation classification can be determined; The area of land deformed by the landslide can be cleared (Miyagi 2013).

Based on knowledge of geomorphology, characteristics of vegetation cover, drainage conditions, signs of surface displacement in the form of landslides such as scarps; irregular or hummocky topography below scarps, at the body; bare linear tracks oriented downslope; fresh rock exposure; fresh rock accumulation at the slope base; disordered vegetation and disarranged drainage... are realized.

These signs are analyzed and compared with an identification catalog of characteristics of landslide types such as Rotational slide, Translational slide, Compound slide, Debris slide, Debris Flow, complex slide, etc., from which the type, features, and evolution of the past displacement process can be determined, interpreted and recognized. However, the aerial photograph is a similar image. The interpretation of topographic information from vegetation images was used as a method of information collection. Depending on the image quality and scale, some positions or features within the slider block are not clearly defined. In such cases, it is necessary to conduct an actual field survey. The information on landslide features is recorded as a landslide identification information layer. The landslide distribution topographic map is created by the combination between the landslide identification information layer and the topographic information layer.

The method of building topography maps by aerial photo interpretation in Vietnam has been applied since early. However, the landslide inventory maps have only been carried out and published after 2000. A typical example of Landslide identification and mapping is a landslide inventory map along HCM road (Central region of Vietnam), which has been carried out and published in 2016.

Figure 1 is the landslide distribution map of the Kham Duc area, in Viet Nam—one of the 6 first sheets of landslide inventory maps. Based on the analysis of more than 100 black and white aerial photographs on a scale of 1/33,000, ninety-six landslides were recognized, with 5 types of landslides including (1) Rotational sliding; (2) (Translational sliding; (3) Complex; (4) Debris sliding; (5) Debris flow. Of the five types, the first three are identified by topographic and topographic form characteristics; the other two types are identified by the topographical features of the sliding body.

Currently, remote sensing image technology is being increasingly developed and provides better quality land surface images for analysis, but landslide identification based on interpretation of images taken from aircraft is still considered the basis for landslide identification, which has been carried out in Vietnam.

#### 3.1.2 Application of Landslide Identification Using Unmanned Aerial Vehicles (UAV) in National Road Survey of Vietnam

Remote sensing imaging technology using unmanned aerial vehicles (UAVs) for landslide terrain recognition has become common in the field of landslide disaster prevention in many countries, but its application for survey and design of prevention and mitigation works in Vietnam has not been popularized. Research and application of remote sensing imaging technology using unmanned aerial vehicles (UAV) in landslide surveys of roads in Vietnam is a requirement set by the Ministry of Transport (MOT) to ITST the research team.

The experiment was conducted at the road connecting Lao Cai-Sapa, National Highway 4D, Highway 7-Nghe An Province, and Ha Long City—Quang Ninh Province using a UAV Phantom IV. The images were taken from the UAV with a larger than 70% overlap area. Classifying of photos, and handling blurry and noisy images were carried out with specialized software. The overall image of the target area was built by combining coordinates of UAV photos in the same GIS geographic coordinate system and correcting through the coordinates of the ground control point (GCP). The orthogonal image model and Digital surface model (DSM) were built from cloud point technology and automatically recognize similar points. Photograph of the area and contour maps, which were constructed from DSM-assisted landslide identification. Figure 2 depicts the development of a landslide topographic map of the section KM 119-Km121, National Highway 4D, Vietnam.

Through the study and evaluation of the type of UAV, the method of photography and interpretation analysis, the advantages and disadvantages of the method compared with conventional survey and images taken by UAV equipment, developing the landslide occurred map was considered feasible.

The advantages of this method are low cost, short implementation time, and high access capacity to hazardous locations where landslides are occurring. For the preliminary landslide survey, the 1:1000 scale landslide topographic map is suitable. The detail of the GSD ground image is proportional to the flight height, (the lower the flight height, the higher the detail image we can get). To build the landslide topographic map with a scale of 1/500 to 1/1000, UAVs fly heights within 50 to 150 m are suitable. To identify the microfeature of the sliding block such as cracks, scrap, etc., a GSD of at cm/pixel is required. However, the biggest drawback of this method is the uneven vegetation cover on the soil surface. In such areas, the Digital Elevation Model (DEM) will be built from the DSM after removing the vegetation cover elevation or comparing it with the available topographic elevation documents.

Although there are still limitations, this topographic survey method still has undeniable outstanding advantages of creating a panoramic view of the landslide object and short implementation time. This method is also safe for operators, and especially suitable for emergency response when a new landslide occurs.

#### 3.1.3 Landslide Mapping through Alos World 3D Mapping (AW3D) and Google Earth

Landslide identification through stereo pair aerial photograph interpretation is considered a primitive technology for the construction of landslide distribution maps. However, in Vietnam, this source of air photo data is limited in quantity, image scale as well as shooting time. With the rapid development of remote sensing imaging technology, taking pictures of the entire surface of the earth has become common and available. Digital images with three-dimensional coordinate information of the land surface in various scale formats through services such as NASA's SRTM can be used as an

Fig. 2 Developing landslide topographic map of the section KM 119-Km121, National Highway 4D, Vietnam using UAV (Thanh et al. 2020)

alternative to stereo pair aerial photographs by traditional technology in building stereoscopic images.

The landslide identification map of 70 km along National Highway 7—Nghe An Area—Vietnam was conducted to set up a test based on the above idea. Experimentation with 3 representative locations was conducted from AW3D data with 10 m contour generation. The comparison of the landslide interpretation results of the sliding block such as landslide boundary, main scarp, and landslide body with the actual ones of the landslide through the field survey showed similarities.

The AW3D data with a 5 m grid size, has almost the same level of detail as the 1/2000 scale aerial photograph used. Topographic maps with contours generated from the above DSM data combined with visualizations from Google Earth are used for analysis and identification of landslides along the route. Different viewing angles to Google Earth and Landform from topographic maps with contour lines from 5 to 10 m have helped identify small to medium-scale landslides with a width of 50–200 m (Fig. 3).

Landslide mapping through Digital 3D World map (AW3D) and Google Earth offers many advantages over traditional aerial analysis, but it still has its weaknesses due to the use of DSM for analysis. In some areas, "fake" main scrap may be identified where there is a sudden change in vegetation cover with high height.

#### 3.1.4 Assessing Landslide Reactivation Potential and Risk Evaluation Mapping for Occurring Landslides

The next issue with assessing landslide risk for an area after the landslides are identified is to compare their susceptibility to reactivation. The ability to reactivate a landslide depends on 3-factor groups including Trigger factors (rain phenomena, earthquakes), Characteristics of the sliding mass (type of motion, and geometrical and geomorphological features), and Internal factors (geology, hydrology). The trigger factor group is a passive factor and the sensitivity to the landslide reactivation is proportional to the magnitude and frequency of the phenomenon that their potential did not study in this research. Excluding the trigger factors, when assessing the risk and building the risk assessment map for humid tropical areas like Vietnam, 2 group factors landslide characteristics and internal factors have been considered.

The groups of feature elements of the landslide are considered from the perspective of geomorphology and divided into sub-groups according to the point of view of Miyagi et al. 2004 including (1)The micro landforms of the soil body as an aspect of the characteristics of movement; (2) The boundary of major landslide components as an aspect of the time process and (3)The landslide topography and the adjoining environment as an index of geomorphic setting. In each sub-group, the related geomorphological member factors that affect the reactive ability of the sliding block were mentioned and classified by a score (Fig. 4).

As for the internal factors, the geological factors mentioned include geologic age, bedrock lithology and structure, surficial geology, and level of weathering. Each geological factor is classified into different features or levels that describe the susceptibility to landslide reactivation and are characterized by a certain number of scores (Fig. 5).

Based on the discussion, the assessment of each factor affecting the reactivity is divided into different levels which are specified by a certain weight score value using the AHP model. The susceptibility of different landslide sites to reactivation depends on the total AHP score, in which geomorphology will account for 44.44% and geology will account for 55.56%.

Figure 6 depicts a landslide risk map in the area of Thanh My—one of 6 landslide risk maps, which were developed based on the identification map and risk assessment method which is mentioned above. For these maps, the landslide reactivation potential is divided into 4 levels AA: very high, A high, B medium, and C low. This landslide risk assessment map is one of the first and most important ones in Vietnam for evaluation of the landslide reactive susceptibility to occurring landslides.

#### 3.1.5 Landslide Potential Assessment and Landslide Susceptibility Mapping

For Landslide Risk Evaluation on natural slopes where landslides have not occurred, an assessment of the sensitivity to vulnerability of the slope by sliding was carried out.

The basic principle for evaluation is based on "past and present are the keys to the future" (Vaners 1984; Carrara et al. 1991). Under this hypothesis, future landslides are likely to occur under the same geological, geomorphological, and hydrogeological conditions as having occurred with previous landslides. The conditions that led to the landslide can be used to identify possible landslides in similar areas in the future.

On that basis, surveys and statistics on the occurrence of landslide phenomenon were conducted for the study area. The Landslide distribution map was developed for the target area. The main causative factors related to the occurrence of sliding block displacements such as slope angle (geomorphology), type of rock, fault density (geology), distance to the road, land used (human being), and precipitation (climate) are selected for assessment. The affection of causative factors to each occurred landslide was discussed and recorded.

Figure 7 is a score comparison matrix of causative factors and the classes within each factor, as required by the AHP method.

The causative factor maps were developed on the same scale from available data, in which each one was classified for assessment. The number and density of occurred

Fig. 3 Depicts an interpretation of landslide mapping through World Digital 3D (AW3D) and Google Earth maps of part of a 70 km mountain area along National Highway 7 of Vietnam. (a) image is taken from

Google Earth, (b) landslide identification map on AW3D background. (c) LS1 and LS2 location identification details. LS1 and LS2: detailed images of 2 locations (Dung et al. 2016)

landslides for each class are estimated by superimposing the landslide distribution map with the causative factors map in the GIS system. The sensitivity to a landslide of each class zone of causative factor maps is calculated and evaluated through the value of the number and density of occurred landslide. The weight value point was given to each causative factors map depending on their sensitiveness and their classes then an analytical hierarchical process (AHP) is used to combine these maps for landslide susceptibility mapping.

The landslide distribution map and Landslide susceptibility map of the corridor area, along HCM road from Quang Tri to Kontum in the center of Viet Nam are created from overlap landslide causative factors maps with calculated Eigenvectors from the AHP model.

Fig. 4 Geomorphological integrated inspection sheet for landslide risk evaluation for the tropical region (Miyagi et al. 2004)

According to the Landslide susceptibility map presented in Fig. 8, susceptibility to land sliding was divided into 4 classes very high, high, moderate, and low. The calculation showed that 82.66% of over 600 occurred landslides in the distribution map fall in the high and very high susceptible zone.

For each study area, the accuracy of the Landslide susceptibility map depends on the data and basic parameters selected to calculate and assess the risk of landslide hazards presented in the form of maps in the GIS system. The selection of input map data to calculate landslide hazard risk depends on three main factors, namely "relevance", "availability", and "scale" of the map." Relevance" shows the close relationship of the main factors related to landslides in the study area. "Availability" refers to the available data and the data likely to be obtained in the study. And "scale" of the input map refers to the map scale of the factors affecting the landslide process that will be used to calculate the risk of landslide hazard for the study area. The accuracy of the map

Fig. 5 Geological integrated inspection sheet for landslide risk evaluation for the tropical region (Luong et al. 2016)

is characterized by the number of landslides occurring over a highly susceptible zone.

#### 3.1.6 Digital Database Structure on Topography, Geology, Hydrology, and Landslide Identification for Landslide Mitigation in Survey and Design Work

Based on researching and applying digital databases for the management of landslides and disaster prevention in the world, an orientation to create and apply a database for storing, managing, and proposing landslide mitigation solutions is created. The built-in landslide data layer is considered a separate layer in the structure of many different data layers in the same geographic coordinate system GIS, which is known as Big Data. The research objective is to build a database structure on landslides including the information on topography, geology, and hydrology relating to landslide identification for landslide response and mitigation for traffic in the mountain zone. The data structure consists of two parts including Assessing the level of risk and Countermeasure selection.

#### 3.1.7 Assess the Level of Risk

Besides spatial and temporal parameters as well as time and type of movement, relevant factors are divided into groups such as the Topographic group (length, height, natural slope gradient angle on the upper slope, distance from the foot of the slope to the road, and a number of steps on the slope), Geology group (slope materials, degree of weathering, the depth and strike of the material layer, cracks; and Hydrogeological and hydrogeological groups (daily rainfall intensity and signs of groundwater). The survey sheet for landslide collecting data is presented in Fig. 9. Each factor is again assigned a certain weight depending on its importance to the degree of susceptibility to displacement.

The weighted model (AHP) is then used for the classification and evaluation of landslides inbuilt stores, in which The total score (maximum 100) of the risk factors for each landslide site is divided into 5 levels Very High Risk, High Risk, Medium Risk, Low Risk, Low Risk, Very Low Risk with scores as 100–80, 80–60, 60–40, 40–20 and 20–1, respectively. (Thanh et al. 2020).

Three special factors of sliding blocks mentioned as Direction of discontinuity, Wethearing, and Groundwater are used to evaluate the level hazard of sliding blocks. Depending on the presence of these factors during the survey, the hazard level was divided into five levels, with the level increasing gradually. Table 1 presents the principles of assessing the hazard level of Landslides.

#### 3.1.8 Countermeasure Selection

Based on assessing the level of risk and level of Hazard, the response and mitigation solutions are considered and selected. A detailed survey of the selected locations is conducted for further evaluation and countermeasures selection. Three groups of countermeasures include the impact mitigation Control works; Prevention works and monitoring and early warning work are given and recommended for

Fig. 6 Landslide risk assessment map of Thanh M~y -Vietnam (Luong et al. 2017)

applicability according to characteristics and recommended levels of danger. Depending on the actual situation of each landslide, suitable solutions will be selected.

The successful application of research results for building a database for National Highway NH4D, NH 6, and NH 7 in Vietnam is the first step for applying Big data in managing landslides along the roads.

#### 3.2 Landslide Simulation and Testing

#### 3.2.1 Development of Untrained Dynamic-Loading Ring Shear Apparatus

The dynamic-loading ring shear apparatus is Prof. Sassa's Invention in 1992(DPRI-3). ICL 2 is the sixth generation

Fig. 7 AHP modal for landslide causative factors and the classes (Tien et al. 2016)

device that was developed to donate it to Vietnam together with the technological transfer.

Like other shearing apparatus, ICL 2 was designed for the Physical simulation of landslides. It can reproduce stress on the potential sliding surface within a slope during rainfall,

Fig. 8 Landslide distribution map and Landslide susceptibility map of the corridor area, along HCM road from Quang Tri to Kontum in the center of Vietnam (Tien et al. 2016)

Fig. 9 Survey sheet for landslide collecting data and item and score of relative factors for landslide risk assessment. (left) and the matrix of score evaluation of causative classes. (right)

earthquakes, and both. It can also measure the shear displacement and pore pressure, as well as the mobilized shear resistance during shearing (Figs. 10 and 11).

The ICL-2 has six main components, including (1) Computer control system, (2) Main control unit for control and

Table 1 The principles of assessing the hazard level of Landslides

monitoring, (3) Instrument box, (4) Power supply box, (5) Pore-water pressure control unit with backpressure unit, and (6) de-aired water and vacuum system. The overview of ICL-2 is shown in Fig. 10.

The important improvement of ICL 2 compared to previous models is the sample box with 100 mm inner diameter, 142 mm outside diameter, and the largest sample height of 52 mm to create a shearing area of 79.79 cm2 and Max. shear speed (cm/s) of 50 cm/s and the Max. Pore water pressure and the Max. normal stress up to 3000 Kpa. ICL2 is capable of simulating undrained shear state, pore-water pressure control state, and monitoring earthquake state.

After ICL-2 donated version has been completed, it has been tested by Vietnamese long-term and short-term trainees for around two years. All trouble sources were solved, and all trainees had the confidence to use ICL-2. Manuals via video

Fig. 10 Undrained dynamic loading ring shear apparatus ICL-2

and written materials were developed for use by future trainees. The video manual made by ITST is included in Landslide Dynamics: ISDR-ICL Landslide Interactive Teaching Tools.

#### 3.2.2 Mastering the Use of the ICL2 and Applying it to Study Rapid Landslides in Vietnam