Time-dependent analysis of stability of surface coal mine spoil slope under groundwater pressure

The objective of this investigation was to develop an effective and efficient analysis procedure for understanding better the stability aspects of spoil piles which are susceptible to build-up of groundwater pressure with time. The procedure involves two distinct research areas. First is the analysis of groundwater conditions in the pile. The second is the stability of the pile under the groundwater conditions. The procedure utilizes fixed and variable input parameters. Fixed parameters include spoil pile material content, mode of pile formation, pile geometry and orientation. The variable parameters are spoil permeability, different sources of water inflow and time. In this procedure, the transient groundwater conditions are determined by a finite element modeling technique. After establishing the development of phreatic surface with time, and knowing the strength parameters, a zonalized cross-section and failure mode, the stability analysis is done by an appropriate limit equilibrium method. The procedure was extensively validated using hypothetical and real world data. The research shows that the spoils with saturated hydraulic conductivity and effective average rainfall in a ratio of 1.0 or less are more sensitive for build-up of groundwater pressure with time. The model predicts better results for spoil in areas where average rainfall is well distributed over a year.;The simulation technique developed in this thesis can be used to find an optimum spoil configuration and to analyze stabilization aspects of unstable abandoned mine slopes. The technique, along with measurement of water levels, can be useful for monitoring spoil pile stability and for providing warning of impending stability problems. However, there is very little information on hydrological and strength parameters of mine spoils. Acquisition of more data is needed for better understanding and development of a more accurate model for predicting the transient influence of groundwater on not only spoil piles but also waste piles, tailing dams, embankments and other similar accumulations of materials from mineral and other industries.