Dynamic Distortion and Long-Term Settlement of Weathered Argillaceous Siltstone under Subway Tunnel Base in Nanchang, China

Abstract

Subway tunnels in Nanchang, China, may pass through one or several weathered argillaceous siltstones in the construction process. To reveal the influence of weathered argillaceous siltstone on the long-term settlement of subway tunnels, dynamic triaxial tests of intensely and moderately weathered argillaceous siltstone were carried out. Based on these tests results, the evolution law of cumulative plastic dynamic strain was analyzed and a prediction model of cumulative plastic strain was established. Finally, an actual subway tunnel with weathered argillaceous siltstone was selected for long-term settlement prediction analysis. The results of settlement prediction indicate that the sedimentation value of this tunnel is approximately 20.87 mm under 100 years of operation (service life). Research results show that the dynamic strain of weathered argillaceous siltstone under cyclic vibration load is mainly affected by dynamic stress and static deviatoric stress. When the static deviatoric stress increased from 0 to 200 kPa, the dynamic strain of intensely and moderately weathered argillaceous siltstone increased by 8.53 and 5.97 times, respectively. Therefore, the intensely weathered argillaceous siltstone (IWAS) is more susceptible to static deviatoric stress than moderately weathered argillaceous siltstone (MWAS). In addition, increasing the confining pressure will accelerate the expansion of fissures in intensely weathered argillaceous siltstone, while the fissures in moderately weathered argillaceous siltstone will be inhibited, and the effect is completely opposite.