Analysis of Ground Settlement Caused by Shield Passing Through the Area of Long-term Precipitation

The main stratum of Chengdu rail transit construction is sandy pebble stratum, which is mixed with a large number of fine particles. Some EPB tunnels need to cross the existing cut and cover stations with long-term precipitation. The vertical displacement of soil mass during construction is significantly different from that in the area without precipitation. Soil structure, settlement mechanism, settlement control mode and engineering examples in long-term precipitation area were analyzed, and conclusions are as following: (1) long-term precipitation of foundation pit will lead to the loss of fine particles in the sandy pebble stratum, forming a skeleton pore structure; (2) the properties of grouting and improved grouting materials have a significant control effect on the vertical displacement of soil caused by area of fine particle loss due to long-term precipitation; (3) the largest proportion of settlement is caused by the shield tail out stage when the precipitation area is not entered, the proportion of soil consolidation settlement and cutter arrival stage increases after entering the precipitation area. The conclusions have been verified by the shield engineering of Ming-Jiu section of Chengdu rail transit Line 17, and the research results can provide theoretical basis and reference value for similar projects.