PHYSICAL MODELLING IN ROCK SLOPE STABILITY EVALUATIONS
Abstract
In addition to the well-known planar and wedge type failure modes in rock slopes, several secondary modes of failure may also occur in open pit mines. These include slide-toe-toppling, slide-head-toppling and "cantilever-type" failure. In this research these failure modes were studied using both physical modelling and analytical techniques, with the physical modelling technique incorporating an inclinable base-friction table. Results indicate that the major controlling factors for both slide-toe- and slide-head-toppling failure modes are (i) dip of the bedding plane; (ii) interblock and blockbase friction angles and (iii) block weight ratios (BWR). The factors that control the stability of the "cantilever-type" failure mechanism are (i) length of protrusion of cantilevered block; (ii) thickness and weight of cantilevered block; (iii) weakness planes, their distribution and frequency in the cantilevered strata and (iv) the weight of rock overlying the cantilevered section. Some field behavior patterns of rock materials on a slope prior to failure were also studied using physical models. In this work, emphasis was placed on the shape and configuration of the slope blocks. Results from these tests indicate that (i) the failure of a rock slope is time-dependent. A general relationship obtained which relates elapsed time and cumulative horizontal displacement of any rock slope block, has the form LogU = mLog(t/t(,1)) where U = cumulative horizontal displacement of slope blocks; t = elapsed time; t(,1) = time intercept and m = time exponent (slope of obtained straight line); (ii) there is commonly a gap opening between slope blocks in the top and sometimes intermediate layers of a given slope geometry; (iii) a possible backward rotation of top and intermediate layer slope blocks, commonly results in the closure of earlier formed tensile openings; (iv) an initial vertical displacement (positive or negative) of fore-slope blocks due to slumping (or rotation) and (v) eventual progressive failure of the rock slope beginning with the fore-slope working inward with time.
Degree
Ph.D.
Subject Area
Geology
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