Numerical Investigation of Mining-Induced, Hydromechanically-Coupled Responses for a Nevada Mine Site

Abstract

ABSTRACT Understanding the coupled interaction of rock and water under stress is often a key factor in assessing slope stability in open pit mining. In this paper, a numerical modeling research project is presented which demonstrates the concept of hydromechanical coupling (HMC) and assesses the sensitivity of contributing parameters to pressure responses observed in a piezometer sensor due to excavation of a mine slope. Site monitoring data showing HMC effects within a mine in Nevada are analyzed and reproduced using FLAC. This research aims to promote the understanding of HMC in pit slopes and provide improved guidance on how to plan mining activity, monitoring and slope design to incorporate the benefit of HMC effects. INTRODUCTION Open-pit mining is a dynamic process that involves the excavation of earth materials to retrieve ore. During the mining process, changes to the physical properties of the in-situ rock mass are induced. As excavations progress, pore pressure changes occur beyond the slope face, and, while some factors such as infiltration or recharge may increase the pore pressure, others may help reduce it. Consequently, understanding the relation between pore pressure changes and rock deformation is a key factor in ensuring the stability of slopes and maintaining safe mining conditions. Pore pressure can be measured, predicted, and managed through active dewatering and depressurization programs to control stability. In this research paper, 2D modeling using FLAC v8.1 is presented to help explain observed behaviors in piezometer monitoring data from a mine site in Nevada, and to provide a hydromechanical explanation for these behaviors using simple model illustrations. Different case scenarios using a variation of mechanical and hydrological input parameters are performed. Varied parameters are those which govern pore pressure responses caused by induced changes in total effective stress (unloading) of the rock mass, such as elastic modulus, porosity, and permeability. Results are presented and discussed for each modeling case scenario using pore pressure history at a point representing the piezometer sensor location.