Quantifying Mining Induced Rock Mass Damage in Open Pits

Provider: Itasca Consulting Group


Open pit excavation results in disruption of the in-situ stress field with some stresses being relieved and others being increased. Damage to the rock mass behind open pit walls results from this stress redistribution and blasting practices. Damage to the rock mass from both causes has important hydromechanlcai effects. i.e. damaged rock has lower rock mass strength and stiffness. But, also higher permeability and porosity. Presently, mechanical damage is crudely accounted in standard stability analyses by using the D-factor in the Hoek-Brown estimate of rock mass strength. Choice of the D-factor and its distribution behind the pit wail often depends on the practitioner’s experience and intuition; there are no clear guidelines for quantifying mechanical damage. Some recent slope failures can be traced to poor understanding of rock mass damage. Quantifying hydraulic changes is even less understood. Thus, there is an urgent need to provide guidelines for quantifying hydromechanical changes.

Quantifying the spatial distribution of rock mass damage (rock mass strength degradation or the D-factor in the Hoek-Brown criterion or damage zone characterisation) behind open pit walls due to stress re-distribution (as a result of pit excavation) and blasting practices and its influence on hydromechanlcail behaviour of rock masses are the project objectives. Bio-Up (blasting damage simulation) and Slope Model (simulating hydromechanical changes due to pit excavation) codes will be used to allow quantification of hydromechanical changes.