A Study On The Long-term Settlement Of The Metro Tunnel In Saturated Soft Soil

With the continuous development of China's economy, the process of urbanization has been accelerated, making the land resources increasingly scarce, the traffic situation is deteriorating gradually. As an effective measure to improve the traffic condition and save the land resources, the subway has developed rapidly in recent years. During the operation period, the subway tunnel bears the long-term cyclic load, which is the cause of the settlement problem. Without effectively controlling, large settlement will cause a serious impact on the operation of the subway. In this paper, the method for predicting the long-term settlement of the tunnel in saturated soft soil is studied.This paper firstly summarizes the previous research achievements about the long-term settlement of tunnel. The influence of accumulation on soil deformation and pore pressure of initial consolidation condition is discussed based on the study of the cyclic softening characteristics of saturated soft clay. An effective stress stiffness degradation model considering initial consolidation state is proposed based on the results of laboratory tests of saturated soft clay. The stiffness degradation model is accomplished by secondary development of ABAQUS field variable subroutine,which has been compared with the result of simulated indoor tests.The threshold cyclic stress ratio is taken as the limit to divide the soil mass into parts. When the stress state is lower than the threshold cyclic stress ratio, the soil is calculated by considering pore pressure accumulation stiffness degradation model.And the results are not only compared with the results of which calculated by considering the pore pressure accumulation stiffness degradation model, but also the results of without considering the stiffness degradation.A three-dimensional finite element model of soft clay and shield tunnel is established. Considered the influence on stiffness degradation model, the threshold cyclic stress ratio is applied to the calculation of deformation of soft clay, the accumulative settlement of shield tunnel in soft soil under cyclic loading is calculated.The influence of the factors such as the operating speed, property of soil, the threshold cyclic stress ratio, lining thickness, the depth of the tunnel on the long-term settlement of the tunnel are considered, the finite element calculation model corresponding to the actual project is established and compared with the measured data of tunnel settlement.And some conclusions are drawn after analysis.