JOURNAL PAPER

Importance of pore pressure monitoring in high walls

K.L. Morton^I; M.C. Muresan^I; F. Ramsden^II

^IKLM Consulting Services
^IIDebswana Mining Company

SYNOPSIS

Groundwater and associated pore pressure represent elements that can have a negative impact on surface mining and slope stability. Groundwater flow and deformation within a slope influence each other. An increase in pore pressure will result in a decrease of effective stress; and conversely, if the pore pressure decreases, the effective stress increases. Slope analysis and slope design calculations require good information on pore pressure distribution around an open pit excavation. Until recently very little pore pressure data were available and assumptions had to be used.
Location and design of measuring points depend on geological and structural setting, geotechnical domains and practicality. Good planning and the use of sensitive point piezometers to measure in situ pore pressures means that real-time data can be collected and used for the construction of flow nets, the determination of pore pressure distribution around an open pit mine, the validation of the dewatering/depressurization requirements, the calculation of the efficiency of the dewatering system and finally the use of pore pressure data in slope stability analysis. The recommended layout for a monitoring system, types and design of piezometers, data collection and use of the pore pressure data are presented.

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References

ATKINSON, L.C. The Role and Mitigation of Groundwater in Slope Stability. Slope Stability in Surface Mining. 2000.         [ Links ]

FREEZE, R.A., and J.A. CHERRY. Groundwater. Prentice Hall. 1979.         [ Links ]

HYDROLOGIC CONSULTANTS INC. Simulated Hydraulic Heads in Highwalls at Orapa Pit as a Guide for Selecting Locations and Depths of Piezometers. Technical Memorandum. 2004.         [ Links ]

KLM CONSULTING SERVICES. Drilling of Sandstones Observation Boreholes around AK1 Pit, Technical Report for Debswana Mines. 2006.         [ Links ]

Large Open Pit 2008 (in press), Project design guidelines (G Beale).         [ Links ]