Fully coupled simulation of an opencast mine subjected to earthquake loading

Abstract

Earthquake stability assessment of large opencast mine slopes are complex and non-linear problems, often addressed using pseudo-static approaches neglecting material-induced failures and the role of pore-fluids. In this study, a numerical approach is used to understand the dynamic response of saturated and partially saturated soils. For this purpose user-defined elements have been implemented in Abaqus/Standard including user-defined material models. The governing equations involving coupled fluid flow and finite deformation processes in partially saturated soils are derived within the framework of the Theory of Porous Media. The stress-strain behavior of granular soils is represented by a hypoplastic constitutive model and for clayey soils the ISA-Clay model is used. The saturation-suction behavior is modeled using the van Genuchten model. To account for the large scale of the finite element model, a scaling procedure of the system of equations is proposed to purge the influence of initial stress. The performance of the user-defined elements is tested by back analysis of a centrifuge test available in the literature. Finally, large-scale fully coupled finite element simulations are performed to study the response of a flooded opencast mine under earthquake loading. The paper illustrates the importance of accounting the pore-fluids as independent phases in the context of seismic analysis of slopes and the influence of simplifications on which the calculation is based are highlighted. The simulations show strong wave diffraction effects for inhomogeneous dump structures, resulting in smaller displacements in near-surface areas of the slope. Further it was found that large areas of the dump show a temporary decrease of effective stress. The initial strong differences in stiffness between the different materials may decrease with time after several seismic events due stress redistributions caused by earthquakes.