Seismic stability analysis of 3D tunnel faces in unsaturated soils

Abstract

This paper aims to develop a framework using the kinematic approach to assess the face stability of tunnels in unsaturated soils under seismic conditions, allowing for a rigorous upper-bound solution of the required face pressure. The stress behavior of the soil under steady unsaturated infiltration is analytically described using a suction stress-based framework. Three methods, i.e., the pseudostatic (PS) method, conventional pseudodynamic (CPD) method, and modified pseudodynamic (MPD) method are employed to represent the earthquake acceleration for the seismic analysis of tunnel face stabilities. The temporal and spatial variations of seismic accelerations and suction stresses are incorporated into the work-energy balance equation within the 3D discretization-based failure mechanism. A hybrid optimization routine is employed to search for the maximum required face pressure. The developed framework is validated through a comparison analysis with prior research, and the outcomes obtained from the three methods of representing seismic accelerations are compared. Several parameter analyses are performed to discuss the effects of the unit weight of unsaturated soils, dynamic characteristics, and hydraulic hysteresis. The framework can provide a useful tool for quantitatively analyzing the impact of potential seismic forces, as well as steady unsaturated infiltrations paired with hydraulic hysteresis, on the tunnel face stability.