Strata Subsidence Characteristics of Shield Tunneling In Coastal Soft Soil Area

In order to study the subsidence characteristics caused by large diameter shield tunneling in coastal soft soil area, based on the project of North Oujiang shield tunnel in Wenzhou City, the displacement field, seepage field and stress field of surrounding rock during shield tunnel construction process under fluid-solid coupling were analyzed by using finite difference method. The results show that when the shield tunneling passes through the monitoring section of the tunnel, the surrounding rock in a certain range of this section above the tunnel will be uplifted. Shield tail grouting can effectively control the settlement of the ground, and the increasing range of the ground subsidence gradually decreases. With the advance of the shield the pore water pressure increases, and the pore water pressure in the soil layer will rise sharply due to the shield tail grouting. When the shield passes through the monitoring section of the tunnel, the strata stress above the tunnel increases due to uplift extrusion, and the strata stress below the tunnel decreases due to stress releasing. When the grouting at the tail of the shield is completed and gradually moves away from the monitoring section, the stress releasing results in the decrease of the stress in the surrounding stratum and shows a funnel-shaped form.