A study on influence of excavated shallow tunnel on design parameters of ground motion in the soft site

Considering the characteristics of soft soils in Nanjing, a representative soft site is selected in this paper. Firstly, the curves of dynamic shear modulus ratio G /Gmax 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 for the subways built in Nanjing are concerned, the influence of excavated shallow tunnel on design parameters of ground motion is analyzed by 2-D finite element method. In this calculation model, the effect of dynamic soil-tunnel interaction is considered and the behavior of soil nonlinearity is considered by the equivalent linear method. The design parameters of ground motion in the soft site are compared with those of free ground. It is obvious that the excavated shallow tunnel has great influence on the design parameters of ground motion in the soft site. In this paper, the approximate range and degree of influence of excavated shallow tunnel on design parameters of ground motion in the soft site are given and the rules of variation are generalized. The present conclusions can be referenced in seismic design of buildings which are adjacent to excavated shallow tunnels, and great attention should be paid to the influence of shallow excavated tunnel on design of parameters ground motion.