A geomechanical numerical modeling research project is being conducted for the Stillwater Mine located in Nye, Montana. The project involves identifying potential ground control problems and exploring various methods of modeling the behavior of the rock, with objectives of improving underground safety and facilitating optimum support design. During the preliminary modeling stage of the project, it was determined using continuum-based approaches that the discontinuities can control the behavior of the rock; the data collection system at the mine was subsequently adjusted to provide more information about the rock joints. A parametric study of possible underground conditions at one specific site was then conducted using discrete element methods. The results compare well with a rough analysis of the conditions. A discussion of the strengths and limitations of the methods employed and the significance of the results is included.
A geomechanical numerical modeling research project is being conducted at the Stillwater Mine, a large underground platinum/palladium mine located in Nye, Montana. The project involves identifying potential ground control problems and exploring various methods to model the behavior of the rock.
The primary objectives are to improve safety for miners working underground, and to develop a modeling system that will facilitate optimum support design. The work presented here contains selected results of the preliminary stage of the project; this paper is not meant to serve as an in-depth case study but rather as an example of the application of a general methodology which can be used to identify the need for discrete element modeling.
The Stillwater Mine has been in operation for 15 years. At the current time, development consists of more than 5 miles of underground excavations, and annual production is approximately 650,000 tons of ore (anonymous, 2001).
The first stage of the numerical modeling project, the preliminary modeling stage, consisted of two parts. First, numerical models based on continuum approaches, finite element and finite difference methods, were used to calculate the stresses and deformations in the rock mass, and determine the overall response to the planned excavations at one specific site within the mine. The results indicated that the discontinuities can in fact control the behavior of the rock, and are a crucial component of the numerical model. The data collection system at the mine has subsequently been adjusted to provide more information regarding the orientation and spacing of the rock joints.
The second part of the preliminary modeling stage involved developing a geomechanical numerical model using discrete element methods to characterize the behavior of the rock. Discrete element methods were developed specifically to model the behavior of discontinuous materials like jointed rock masses and therefore provide more accurate results than continuum-based methods. In this preliminary discontinuum phase, a parametric study of possible underground conditions at the specific site was conducted to examine the potential range of responses. These predictions will later be compared to the actual rock mass behavior. The site conditions and the details and results of the preliminary modeling stage of the research project are presented in the following sections. This is followed by a comparison of the results with a rough analytical solution, and a discussion of the strengths and limitations of the numerical methods employed.
Many numerical modeling parametric studies have previously been conducted for mining-related applications. Examples include Hart et al 1988, A1Harthi & Henchef 1992, Coulthard