OPEN PIT DEPRESSURISATION
Groundwater and inter-flow can often be a contributing factor to open pit stability issues. High water pressure heads in open pit faces exert a negative pressure which might increases the probability of failure of the adjacent geological strata. The high pore pressures pose a risk at open pits especially when it contains poor ground conditions or rock weak zones and/or very steep pit slopes. Reducing pore pressure results in increased shear strength of the open pit faces; increased rock effective normal stress, increasing friction angles and cohesion.
Reducing high pore pressures not only contributes to a safe mining environment, but often provides an added opportunity for mines and mine design engineers to steepen up pit slopes. Steeper pit slopes could reduce the strip ratio and therefore reduces mining costs.
Conventional out-of-pit and in-pit dewatering might not always be enough to reduce pore pressures. High pore pressures are often associated with lower permeable strata which often require additional dewatering measures, for example horizontal drains. Poorly designed storm water protection measures and water ponding on the open pit perimeter or benches could further contribute to zones of high pore water pressures.
Monitoring of pore pressures is an important step in identifying or confirming risk areas. Pore pressure modelling is furthermore a valuable tool in identifying risk areas and for designing and optimising depressurising measures.
GCS can assist mining clients, geotechnical engineers and mine designers to identify zones with potential high pore pressures, design feasible depressurisation/dewatering systems or monitoring networks, assisting them to create a safe and optimised mining environment.