Probabilistic Analysis of Responses of Tunnel Under the Surcharge Considering Soil Vertical Spatial Variability

Surface surcharge is regarded to be one of the main factors that will cause large deformation of tunnel. On the other hand, it is widely accepted that the soil exhibits significant spatial variability that consequently causes the large variation of structural performance of embedded tunnels. This paper aims to investigate the influence of soil vertical spatial variability on tunnel subjected to the surface surcharge. Herein, the random finite difference method (RFDM) is used. Random fields of elastic modulus E-s of soils are generated and mapped into finite difference analysis to reveal the impact of spatial variability. Given the modeling specifics mentioned above, some results of the numerical simulations are found: (1) the spatial variability may be underestimated if the discretized points in simulating the vertical random field are too coarse; (2) there exists two critical scale of fluctuation: 15 m and 10 m for COV of E-s at 0.15 and 0.35 when evaluating the crown settlement. The estimated value will be high if neglecting spatial variability; (3) the run number for Monte Carlo simulation (MCS) also plays an important role; a converged run number means that the COV of generated data is not sensitive to the run number. In this study, it is about 300 in this sense; (4) the different combination of scale of fluctuation and limiting value will lead to wide range difference when evaluating the probability of exceedance and reliability index. Therefore, it is necessary to consider the spatial variability on analyzing the effect of surface surcharge on tunnel.