Soil deformation and excess pore water pressure caused by excavation of twin-bored tunnels in soft soil

The theoretical solutions for the soil deformation and excess pore water pressure caused by excavation of twin-bored tunnels in saturated soft soil are given. The data from a project of twin-bored tunnels of the Hangzhou Metro Line 2 is used to validate these solutions. The effects of additional thrust, friction between the shield and the soil and tail void grouting on the vertical deformation of the soil are investigated. It is shown that when the shield is close to the reference section, the influence of such parameters on the soil deformation is great. After the shield passing the reference section for a certain distance, the lateral displacement of the ground surface and the excess pore water pressure tend to be stable. The influence of the friction between the shield and the soil on the excess pore water pressure is limited within half the length that the shield has passed. When the shield leaves the reference section, the excess pore water pressure generated by the tail void grouting approaches 0. The research may provide guidance for future tunnel projects in similar soft soil as in Hangzhou.