Study on the Influence of Shallow Excavated Tunnels in Soft Site on Design Ground Motion Parameters

摘要

By considering the characteristics of soft soils in Nanjing, a representative soft site is selected. Firstly, the curves of dynamic shear modulus ratio G/G_(max) and damping ratio versus dynamic strain amplitude γ of the soils in this site are tested by GZZ-1 free vibration column test system (improved and carried out by Nanjing University of Technology). Secondly, as far as the subways built in Nanjing are concerned, the influence of shallow excavated tunnels on the design ground motion parameters are analyzed by 2-D finite element method. In this calculation model, the effect of soil-tunnel dynamic interaction is considered and the behavior of soil nonlinear is considered by the equivalent linear method. The design ground motion parameters of the soft site are compared with those of free-site. It is obvious that the shallow excavated tunnels have great influence on the design ground motion parameters of soft ate. The approximate range and degree of influence are given and the rules of variety are generalized. It is proved that the shallow excavated tunnel is disadvantageous to the seismic performance of nearby superstructures with natural vibration period are about 0.5-1.0s.