Fault factor for the stability graph method of open-stope design

摘要

The lack of a factor to account properly for theeffects of faults on open-stope stability is a current shortcoming ofthe stability graph method. In this method the rock-mass quality, Q,is used together with a stress factor, a rock defect factor and agravity factor to define the stability number, N'. The Q systemdoes not specifically include a factor that accounts for the presenceof faults, yet nearby faults frequently affect the stability of openstopes. In many mines that practices open-stope mining stope wallsassessed as stable by reference to a conventional stability graphoften cave when faults are present. Sloghage of stope walls is amajor concern in mines because of ore dilution.A procedure for calculating fault factors has been developed forincorporation into the stability graph method. The procedureemploys numerical stress modelling to take account of geometricalrelations between faults and stopes, fault characteristics and in-situstresses. It is shown that faults can increase sloughage from stopewalls by their ability to increase sloughage from stope walls bytheir ability to increase the size of the zone of critical low stress instope walls. Faults tend to have the greatest influence on stopestability when the angle between fault and stope is about 20-30°;faults that are nearly perpendicular to the stope wall have littleeffect. The procedure is applied to two case histories fromCanadian underground mines.