ABSTRACT:

Major rock slides in open pit mines are rare but can develop in spite of sophisticated slope engineering design practice. Experience has shown that, except under high seismic load conditions, the serious slope instability condition is almost always accompanied by gradual development of one or more tension cracks behind the slope crest allowing for time-displacement monitoring. Continuous surface displacement measurements with attendant prompt analyses are usually adequate for prediction of slope behavior. This paper describes efforts that have been made to quantify parameters associated with slide movement, and compares the displacement records of several large scale open pit porphyry copper slope failures. Two principal failure stages are recognized in the typical slope failure leading to total collapse: (a) regressive stage during which the failure will re-stabilize if some disturbance external to the rock and structure is removed; and (b)progressive stage during which the failure will gradually displace at an accelerating rate to the point of total collapse unless active control measures are taken. Overall displacement records in both failure stages are apparently of simple exponential form with a definite break occurring at the onset of failure point. Based on displacement rate vs time prior to collapse plots, a semi-quantitative empirical relationship is presented for failure collapse prediction. The comparison of historical slide displacement records furnishes the operating engineer with practical guidelines to estimate characteristics of future large scale slope failures.

INTRODUCTION

The open pit mine is a natural host for rock slides. Small failures are a common occurrence in the typical mine and generally pose no consequential safety or operating hazard. Major rock slides, on the other hand, are rare but have developed and dealt a significant economic and safety impact on, many operations in spite of sophisticated slope engineering design practice.

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