Analysis of long-term settlement of shield tunnel in soft soil area under cyclic loading of subway train

In order to analyze the long-term settlement of shield tunnel under the cyclic loading of subway train in soft soil area in Ningbo, by means of soil dynamic triaxial test in lab, the plastic cumulative strain of silt soft clay in Ningbo was studied under different confining pressures and different cyclic dynamic stresses. The related parameters of the modified exponential prediction model were fitted based on the results obtained from the dynamic triaxial tests of silt soft clay in lab. Numerical simulation was combined with the modified exponential prediction model to predict the long-term settlement of shield tunnel in certain section of Line 1 of Ningbo rail transit by layer-wise summation method. Results showed that track irregularity, the amplitude and frequency of the cyclic loading of subway train had more obvious influence on the long-term settlement of the substratum under the tunnel in the silt soft clay area of Ningbo. Under the same test conditions, the long-term settlement in underlying soft soil with track irregularity was about 2.9 times of that with track regularity. The higher frequency was the cyclic loading of the subway train, the smaller was the induced plastic deformation of the silt soft clay stratum in Ningbo. After 10 years being put into service of Line 1 of Ningbo rail transit, the accumulative total settlement in the underlying soil under the tunnel was about 22 mm. The settlement in the first year was larger, which accounted for about 50% of the accumulative total settlement of the 10 years being put into service. © 2016, Editorial Department of China Railway Science. All right reserved.