BENCH STABILITY IN OPEN PIT MINES: A METHODOLOGY FOR JOINTED ROCK MASSES

The methods used to design ehe global angle of open pic mines are noc adapced (o design ehe benches. This paper presents a mechodoiogy in order co scudy ehe scabilicy of ehe benches. This meihodology is based on geomearical modelling of ehe rraccured rock mass wich provide an assemblage of blocks. The block siability is analysed by mechod based on limic equilibrium. In order co take inco accounc ehe s;aciscicai aspect of ehe discondnuides, an opcimal nu-mber of simulacions is recommended. Thus, ehe resul[s can be incerpreced scatisrically. This mechodology was applied for 22 benches in 5 dufereru mines, ehe resuks obcained are consiscenc wich ehe observed instabilides. When the slopes concain benches and berms is: is noc possible a pdod to elirmnace all risks of failure of ehe same scale äs the benches. Indeed, chis risk is greacer for vedcal or almost venicai facss and ii: would require coo decailed a knowledge of rhe SG""dC;ure of the rock mass, w'nich is noc possible s-c this Stage reasabilicy, for a forecasi co be perfecdy reliable. On ehe ocher hand some degres of risk of failure on a scale comparable wich ehe benches may be accepced if ehe rock falls are haked by horizoncal berms or can be prevenced by local reinforcemenc, installed äs soon äs any excsssive risk is idencified. For these condidons [o be realised, one must be able co predict chese failures and their effects and co have mechods, prevencing chem, available. This paper describes a mean of improving ehe exisring mechods for ehe predicuon and prevendon of bench failures.