Self Drilling Hollow Anchor Bolt Application in Yuxi-Mohan Railway Tunnel

Self drilling anchor bolt is a kind of anchor that integrates drilling, grouting and anchoring functions together. It can construct in complex formations with high construction efficiency and good anchoring quality. Self drilling anchor support can give full play to the self-stabilization ability of surrounding rock, and it is widely used in tunnel surrounding rock support.
Manmushu Tunnel in Yuxi-Mohan Railway is located in Mengla County, Xishuangbanna Prefecture, Yunnan Province, with a total length of 11.6 kilometers and a maximum buried depth of 660m. It is a high-risk control project for the China-Laos Railway. The surrounding rock is grade IV-V, and is mainly mudstone intercalated with carbonaceous mudstone, and the groundwater is mainly bedrock fissure water, which is poorly developed and has a small amount of water. The 30m-buried shallow weathered layer of the DK431+534-564 section of the tunnel entrance is relatively thick, and the double-line V-level reinforced type II composite lining is adopted.

In order to solve the problems of difficult drilling and low construction efficiency of ordinary bolts in special surrounding rock conditions with more weathered rocks, ZYS113 drilling rigs and R51 hollow anchor bars are used for construction, and the single-hole drilling depth is 21m. During drilling, there are 17 holes in each ring at the top of tunnel end face. The hole spacing is 400mm, which is inclined upwardly at an angle of 1-2°. The drilling diameter is 76mm, and each hole is equipped with 3 6m long hollow anchor bar and 1 3m long R51 hollow anchor rods. The overlapping distance between each pipe roof ring is 3 meters. After drilling, the hollow anchor bar can be used as a grouting channel for grouting from inside to outside. The grout is returned from hole bottom. The grouting pressure is 0.4MPa, the water-cement ratio of grout is 0.45, and the pressure maintenance time when the overflows is not less than 10 minutes, which can realize rapid and full penetration of the grout along the rock mass fissures. Pressure grouting can ensure that grout spreading radius is large, and the surrounding rock will be consolidated into a whole to achieve the purpose of permanently anchoring the surrounding rock.
Self drilling anchor bolt has obvious efficiency increase due to its advanced technology. The average drilling time for 21m hole is 40 minutes, and the drilling time for each ring of 17 holes is about 11 hours, and the minimum time is 9 hours. Its economic advantages are obvious.
Self drilling anchor bolt can simplify the drilling, grouting and anchoring procedures. The full length of the bolt is fully anchored, and it can provide a certain supporting resistance immediately after excavation, effectively suppressing the loosening and deformation of the surrounding rock, and avoid or slow down the occurrence of disease accidents during construction and use of the project. The use of self drilling anchor bolt and drill bits can ensure grouting layer is at least 20mm, which fully guarantees the durability of the bolts, and is especially suitable for supporting and strengthening complex formations and broken surrounding rocks.

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