On June 15, in the busy tunnel of the northern section of Metro Line 8, a subway train packed with passengers sped past, and no one noticed that in the Line 8 branch line under construction nearby, a 640-ton giant was quietly undergoing a dismantling project like a "cicada shedding its shell."

The Metro Line 8 branch line passes through Chengyang District and Jiaozhou City, with a total length of 20.4 kilometers, 12 stations, and 12 intervals. The main line tunnel is mainly constructed by the shield method, with local use of the mined method and open-cut method, and all stations are constructed by the open-cut method. CCCC First Harbor Engineering Bureau Urban Transit Company undertook work areas 01 and 02 of the project, with work content including 5 stations, 6 intervals, and 2 ventilation shafts, with a total length of 12.191 kilometers. The shield interval from the starting point to Dajian Station is the ** interval of the Metro Line 8 branch line, of which the right line is 516 meters long and is the ** shield interval of the entire line to achieve single-line breakthrough.

Shield machine dismantling site

This 640-ton giant is the "Yihang No. 19" shield machine. After completing the 516-meter tunneling task on the right line of the shield interval from the starting point of the Line 8 branch line to Dajian Station, it faced a special challenge: due to engineering design reasons, it could not be transported out by conventional lifting methods. The entire shield machine needed to be dismantled and divided into blocks inside the tunnel, then transported horizontally by battery locomotive to the launch shaft and lifted out.

The entire dismantling process was not only complex in procedure but also highly difficult and full of challenges. All dismantling work had to be carried out in a narrow tunnel and required precise manual operation. In addition, the dismantled components weighed up to 55 tons. How to complete turning and transportation within a tunnel with a radius of only 2.75 meters while protecting the finished tunnel from damage was a major problem facing the project team.

Facing these challenges, the project team invited industry experts to discuss the plan, optimized the lifting force distribution, carried out numerical simulation of the transportation process in advance, specially fabricated tooling, and optimized and reinforced the transport equipment. In addition, innovative methods such as "turning tooling" and "chain hoist pulling" were used for component turning and transportation to ensure that the lifting and transportation process was foolproof.

BIM rendering splicing

However, just before the formal shell abandonment construction was about to begin, the project team encountered another "roadblock": the dismantling position of the shield machine was only 3.8 meters horizontally from the operating northern section of Line 8. Any negligence during the dismantling process could threaten the operational safety of the existing line. In particular, the smoke generated during cutting could, if improperly handled, easily intrude into the operating line and trigger smoke alarms, thus bringing operational risks to the existing line. "Safety is always the ** priority; there is no room for any侥幸. This problem must be solved before construction!" said Liu Quan, the project safety director.

"How should the smoke generated during cutting be handled?" At the team-building meeting, the project department widely solicited suggestions from the workers. One worker proposed the idea of "installing a large exhaust fan," which provided the project department with a line of thinking. The project team modified the original starting-point fan and Dajian fan, one for air supply and ventilation and the other for smoke extraction and exhaust. After testing, this indeed effectively solved the problem of smoke accumulation during cutting.

On this basis, Lei Yunsheng, the project's deputy general manager, also required the addition of partition walls and welding fume purifiers to further guarantee effective smoke exhaust. At the same time, the project team continuously monitored the smoke and dust concentration in Line 8, and once the concentration exceeded the specified safety value, construction was stopped immediately.

Ultimately, through a series of efforts, the shell abandonment construction was successfully completed without affecting the operation of the existing line. This marked the complete success of the First Harbor Engineering Bureau's first shield machine "shell abandonment and dismantling" and provided a reference for similar construction in the future.

Now, the "Yihang No. 19" shield machine has been transported to the manufacturer for shell reassembly, making full preparations for the next second launch and the 481-meter shield tunneling task on the left line of the interval.