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UBC Theses and Dissertations

Slope stability and groundwater hydrology research for pitwall design at Equity Silver Mines Ltd., Houston, British Columbia Sperling, Antonin


Structural geology, groundwater, shear strength and blasting control pitwall stability at Equity Silver Mines, Houston, British Columbia. A geotechnical investigation of, these parameters was carried out in the Main Zone pit during the summer of 1984. The objective of the study was to develop a pitwall design based on geologic and groundwater conditions observed in each design sector. This thesis presents the results of the investigation; methods of improving stability by drainage and control blasting are also discussed. Information on structural geology was obtained by line mapping of existing berms. The discodat package of computer programs was used to process the structural data and to identify trends in orientation of discontinuities. Based on this information, the Main Zone pit was divided into ten design sectors, each sector having a consistent pattern of discontinuity orientations, rock type, groundwater conditions and pit wall orientation. Kinematically possible failure modes were identified in each design sector. Failure modes that were expected to present stability problems were analyzed to calculate factor of safety. Pit wall and berm face angles were then selected such that only a small number of potential failure modes will daylight. The stability evaluation has shown that it should be possible to increase pitwall angles by 5〫 in the west half of the pit. However, the data base in this area of the pit is presently limited because only a small number of berms are exposed. Therefore, additional line mapping will be required before the west wall design can be finalized. Groundwater will reduce pitwall stability, especially in the east half of the Main Zone pit. Multi-berm failures are very sensitive to groundwater conditions. A dewatering system should be installed in the Main Zone pit to minimize the possibility of such failures occuring. Wet blastholes dictate that expensive water resistant slurry explosives be used in many areas of the Main Zone pit. The dewatering system should also draw down the water table so blastholes will become dryer and less expensive ANFO can be utilized. The magnitude of shear strength on failure surfaces is required in order to evaluate stability of potential failures. Slip tests, point load tests and back analyses of existing failures were used to determine the shear strength parameters. Further studies should be carried out to better define the parameters at higher stress levels that will develop in a multi-berm failure. Further potential for pit steepening exists if the berm face in the volcanics can be maintained at a slightly steeper angle, e.g. 70 instead of the present 66°. It may be possible to achieve this goal if trim blasting procedures are modified to reduce blast damage to the final wall.

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