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Super "Operator" for the Placement of the Immersed Tunnel Elements

In the world's largest immersed tunnel elements precast yard, CCCC builders created a 180-m-long concrete immersed tunnel element, weighing about 80,000 tons, and as big as a 60-storey building. Then under the guarding of a group of operators, it was transported over 10 km to the immersed site. After all elements were immersed with a cm-degree accuracy in the tunnel foundation trench, they form a 6.7-km-long and two-way six-lane HZMB subsea tunnel, connecting Zhuhai, Hong Kong and Macao.
When a tunnel element was placed, it took Mr. Liu Jiangang over ten hours to pay a close attention to the move of it. How could a man be so careful to control the move of an immersed tunnel element weighing 80,000 tons? For Mr. Liu Jiangang, the chief captain of pontons, the task cannot be accomplished without devotion and responsibility.

From an ordinary sailor to a chief captain of Jin'an 2 and Jin'an 3, two pontons which is built for the placement of tunnel elements, the reason why Mr. Liu can make achievements are that he has a dedicated spirit and keeps learning. How to safely "tow" this big element over 12km and immerse it over 40m deep under water to realize precise “butt joint” are difficult tasks that no one has an operational experience.

Only with the help of the 12 wire ropes precisely controlling the power and angle can we ensure the element winched out in safety. In order to master the operation process of the ponton, Mr. Liu led the crew to exercise for hundreds times in the deep dock. "The role and force condition of each wire rope were recorded on a little notebook in my pocket and I often reviewed my notes so that all the processes were engraved in my mind." Mr. Liu said with the crumpled notebook pulled out from his pocket.
Mr. Liu Jiangang is so familiar with each process and details from element 1 to element 28 that he has many stories to share. Compared with the operation of floating crane, the operation of pontons can’t be observed by eyes. Duo to the measured data submitted by the divers usually are not timely enough, it depends on feelings and experiences to make accurate predictions.

During the period of the element placement, Mr. Lin Ming, the general manager of HZMB Project, often stood behind Mr. Liu Jiangang, with his eyes staring at the change of measuring data on the screen, and his ears listening to the report sent by divers. Although the air conditioner had been open, the clothes of Mr. Liu Jiangang was wet.

Mr. Liu Jiangang felt extremely excited as soon as he was on board, though he has been a captain for more than ten years. "When it rains and has typhoons, everyone ran to home, but we went to the ponton,” he said. When asked why the ponton can be kept so clean, he just said," we treated it as our home." If “Jin'an 2” ponton and “Jin'an 3” ponton are described as two brother pontons, then all of us on these pontons are brothers for we stay on board for more than 300 days a year.

“Jin'an 2” ponton and “Jin'an 3” ponton are the control centers for the element towing and immersion operation as well as the butt joint under the sea. Each keyboard and button here are in connection with the immersed tunnel, each seat here is dedicated to every operator, and each operating rod is controlling the element moving posture and placement accuracy.

After the element was towed to the immersion location, it was 30m far away from the area for butt joint at this time. This distance is full of challenges so that the operator have to move the element slowly. When the element was 1.7 meters from the placement area, the operator achieved "inching" operation, which means controlling the move of element in the range of 1 cm.

Mr. Hu Quanchao is responsible for the operation of the H1, H2 mooring ropes, which control the move of the end of the element. He had practiced for many times before he become a professional operator. He added, “it needs experiences for the precise operation with a range of 1cm, I couldn’t quantify the operation." Compared to the sailor's work, what makes Mr. Hu impressed was the precise operation. Every time Mr. Hu came back home, he often shares many interesting things in his works to his friends.

Mr. Liu Xin took part in the manufacture of pontons in the shipyard of Nantong, Shanghai. Since the first immersed tunnel element was placed, he has been the operator of the L mooring wire ropes, operating 4 anchor machines to let the element placed steadily. It is the most difficult part for us to lift up the element. "There is an inertance for the movement of the element even if you want to stop the operation" Mr. Liu said. Many people treat the operating rod used for the controlling of wire ropes as the game console platform, but only when they get that position will they perceive the heavy pressure and responsibility. What we saw was that some operators worked together, but in fact, it is finished with great efforts from hundreds of people who stand behind them.

As time went back to 2012, Mr. Sou Xuhong was just an ordinary graduate student of Lanzhou Jiaotong University, but now he is a professional surveyor. In the HZMB project, he came into contact with the most advanced measurement technology, such as wireless sonar deep water measuring and controlling system. For the placement of the elements, the HZMB project is the first one applying the wireless sonar measuring and controlling system in the world. Installing that kind of system is one of the work of Mr. Suo Xuhong, who often share his working photos on his moments, winning the admiration from his friend.

In the process of immersion, the sonar measuring and controlling system can measure distance between two points and get the relative position of the three-dimensional direction of tunnel element. After the sonar system measures the position of the element, the operator hands up and down the wire ropes to adjust the relative position of the element.

Each time the placement of one element was completed, Mr. Suo will watched the playback to analyze and record the measurement data. Up to now, a large database has been set up by Mr. Suo and his collegues, and the scientificity of elements placement can be guaranteed by this database.

After knowing the accomplishment of the holding through survey of E28, Mr. Lin Ming, the general manager of HZMB Project, sent a message to Mr. Su Faqiang at six o'clock in the morning, he said, "the placement accuracy of 3 mm, coming from efforts of all workers but not from the hand of god, verified the advancement of our operation technology and equipment system.”

"Every placement operation always is the first time placement operation" is our working idea, which let everyone keep his mission in mind. Looking at the super project in Lingding Sea, every builder feel so proud of themselves that they will cherish this opportunity and look forward to the day when the bridge is open to traffic.

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