Ground motion amplification pattern with TBM tunnels crossing soil-rock interface:Shaking table test

The current aseismic design has seldom considered the effect caused by underlain tunnels.Previous studies focused on the scenarios of tunnels embedded in homogeneous soil under transverse seismic excitation.This paper aims to investigate the tunnel effect on the surface acceleration response in soil-rock strata by shaking table tests.Three sets of excitations are employed and input along the shaking table in both transverse and longitudinal directions.The soil-rock site is classified as four micro-zones with varying conditions,to mount observation stations of acceleration sensors.Dynamic characteristics of the four zones are identified by the transfer function(TF)method,and the tunnel effect on the ground acceleration response is obtained by comparing the spectral acceleration results between the free-field and ground-tunnel models.The test results indicate that the tunnel effect varies with the site conditions.Distinctively,a significant amplification effect is observed at the A4 zone,located on the soil deposit near the soil-rock interface.Then,it is proved that the scattering waves generated at the interface and the standing waves trapped between the tunnel and upper ground surface account for the amplification,revealed by the discrepancies of the TF results and acceleration details between the free-field and ground-tunnel models.

Effect of interface adhesion factor on the bearing capacity of strip footing placed on cohesive soil overlying rock mass

The problem related to bearing capacity of footing either on pure soil or on pure rock mass has been investigated over the years.Currently,no study deals with the bearing capacity of strip footing on a cohesive soil layer overlying rock mass.Therefore,by implementing the lower bound finite element limit analysis in conjunction with the second-order cone programming and the power cone programming,the ultimate bearing capacity of a strip footing located on a cohesive soil overlying rock mass is determined in this study.By considering the different values of interface adhesion factor(α_(cr))between the cohesive soil and rock mass,the ultimate bearing capacity of strip footing is expressed in terms of influence factor(I _(f))for different values of cohesive soil layer cover ratio(T_(cs)/B).The failure of cohesive soil is modeled by using Mohr−Coulomb yield criterion,whereas Generalized Hoek−Brown yield criterion is utilized to model the rock mass at failure.The variations of I_(f) with different magnitudes of α_(cr) are studied by considering the influence of the rock mass strength parameters of beneath rock mass layer.To examine stress distribution at different depths,failure patterns are also plotted.