Soil deformation induced by overlapping tunneling in water-bearing strata

Tunnel construction instability and soil deformation are usually encountered in overlapping tunneling, especially in water-bearing strata. Based on the background of overlapping tunneling of Shenzhen Metro Line 5, numerical analysis is adopted to study the effects of stress relaxation and seepage on the tunnel construction and soil deformation during different tunneling stages. The disciplines of soil deformation are obtained, and the relevant measures are proposed. When the lower tunneling is processed, the soil deformation induced by earth relaxation can be effectively controlled by pre-reinforcement and grouting. After the excavation, the crown settlement becomes steady under the action of groundwater seepage. However, the settlement of the covering layer subsequently comes out because of the soil consolidation induced by groundwater loss. At the same time, the settlement tank develops deeper and wider gradually under the seepage. To avoid its entire settlement, the upper tunnel is recommended to be constructed when its settlement caused by the construction of the lower tunnel is steady. During the construction of the upper tunnel, the earth pressure release induced by excavation brings about large soil settlement, but the seepage causes small settlement. The depth of the ground surface settlement tank develops rapidly, while the radius of the tank keeps constant.