Numerical modelling as a tool in stope design

CIM Bulletin, Vol. 84, No. 951, 1991

R. Pakalnis, Department of Mining and Mineral Processing Engineering, The University of British Columbia D. Tenney, MacLellan Mine, Lynngold Resources Inc., and B. Lang, Detour Lake Mine, Placer Dome Inc.

This paper describes three case histories whereby numerical methods were employed as a tool in the identification of potential instability. Simple two dimensional (PCBEM) and pseudo three-dimensional (BESOL, MINTAB) codes were employed to identify zones of induced stress which were subsequently related to extensometer, stress meter and observational data as the stope was excavated. The following case histories will be discussed. MacLellan Mine — sill pillar stability; Ruttan Mine—Hanging Wall Stability; and Detour Lake Mine—narrow vein mining. The MacLellan case history showed how modelling and instrumentation enabled mining to be conducted safely and under controlled conditions. MINTAB and PCBEM were employed to predict sill pillar failure. The sill pillar failure was associated, with an unloading of stress which was recorded by instrumentation (stress meter) and a decrease in the over-all rock mass strength. The yielded pillar, however, maintained its over-all configuration enabling access through the pillar. The Ruttan case history is an example of hangingwall and foot-wall design whereby the existence of adverse structure coupled with a zone of relaxation results in dilution. BESOL and PCBEM were employed to model a test stope and to verify the observations and measurements through instrumentation. Empirical methods of dilution estimates are employed to determine the level of wall slough with respect to the rock mass rating, stope dimensions and rate of excavation. The Detour Lake case history in an example of open sloping a narrow steeply dipping deposit. Stope dimensions are 135 m in strike length, 47 m in vertical height with an average width (F/W to H/W) of'3.6 m. Stress meters coupled with visual observations are related to modelled estimates of stress and dilution.

Keywords: Rock mechanics, Numerical modelling, MacLellan Mine, Ruttan Mine, Detour Lake Mine, Stope design.