Microscopic Experimental Analysis of the Accumulated Plastic Strain on a Silty Soil Around a Tunnel Under a Subway Loading

With the rapid development of subway transportation systems, the problem of uneven settlement around tunnels cannot be ignored. The soil around the tunnel near the Guoquan Road Station of Shanghai Metro Line 10 was investigated in this study. Through a dynamic triaxial test using a global digital systems, the factors affecting the accumulated plastic strain, such as frequency, dynamic stress amplitude, consolidation ratio, and other factors were considered. The experimental results showed that the accumulated plastic strain on silty soil was related to the vibration times, the amplitude of dynamic stress, and the frequency. Moreover, when the vibration times were constant, the accumulated plastic strain increased with an increase in the amplitude of dynamic stress. In contrast, the accumulated plastic strain decreased with an increase in the frequency. Scanning electron microscopy (SEM) was used to qualitatively and quantitatively analyze the microscopic characteristics of silty soil before and after cyclic loading. Through the introduction of the plane fractal dimension, the relationship between the microstructure parameters of silty soil and macroscopic deformation were established.