Stability analysis of a circular tunnel underneath a fully liquefied soil layer

The present problem deals with the examination of the effect of seismic forces on an unlined circular tunnel in a non-liquefiable general cohesive-frictional soil layer which is located underneath a completely liquefied soil layer. The numerical results are presented in terms of a non-dimensional stability number. The magnitudes of the stability number are determined as a function of thickness of the liquefied layer, tunnel embedment ratio, horizontal pseudo-static seismic forces, friction angle and dilation angle of the soil mass. To conduct this investigation, finite element based lower bound limit analysis is employed. The results are presented in the form of design charts. It is expected that the numerical results presented in this paper would be useful for the practicing engineers.