ABSTRACT:

Open-pit mining in the Tripp Pit, which is located 6 miles west of Ely, Nevada, was discontinued by Kennecott Copper Corporation, Nevada Mines Division, in 1971. Design of pit slopes will be critical in determining the feasibility of resuming operations. The 33-million-ton Northeast Tripp slide is the best understood of several slope failures in the pit. It is a classic wedge failure, which started to fail in 1969, moved an estimated 28 feet toward the pit, then stabilized. The back-calculated strengths of the two controlling faults agrees closely with residual strengths derived from direct shear testing of the high montmorillonite fault gouge (cohesion = 8.7 psi; friction angle = 9.6°). Based on the slide''s rapid acceleration and deceleration due to the cessation of mining at the slide''s toe and precipitation, there is a possibility that the failure''s net driving force was very small as compared to the total driving force. Of the stabilization methods discussed, dewatering combined with either tension cables or a 200-foot catch bench may be the most feasible.

INTRODUCTION

The Tripp Pit is situated in the western portion of the Robinson mining district, White Pine County, Nevada, and is located 6 miles west of the town of Ely, Nevada. Open-pit mining first began in the Tripp area in the early 1950''s. Location of the Northeast Tripp slide and two other failures in the Tripp area are shown in Figure 1. Both the Morris slide and the failures in the transition zone are related to the Northeast Tripp slide. Although Kennecott Copper Corporation, Nevada Mines Division ceased mining the Tripp Pit in 1971, there still remains some potential copper ore below where mining was halted. The economics of mining this material will be dependent on the stability of the future pit slopes.

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