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- 11 - <br />If the rock resists breaking down so that there are sub- <br />stantial voids between individual rock blocks, the shear <br />strength will be controlled by the rock-to-rock contact and <br />interlocking of individual blocks. In this case, waste rock <br />pile material would be classified as a rock fill. <br />If sufficient break down of the material occurs during <br />compaction so that the voids between individual rock blocks <br />are largely filled with fine material, there will be little <br />rock-to-rock contact. In this case, the material will act as <br />a compacted earth fill. The shear strength will be controlled <br />by the strength characteristics of the fine-grained material. <br />In practice, the final character of the waste rock pile <br />will probably be between these two extremes. <br />Blight (1969) indicates that the angle of shearing re- <br />sistance of a rock fill may be estimated from the angle of <br />repose and is generally in the range of 37° to 40°. He adds, <br />however, that the angle of repose applies to the loosest <br />possible condition of the rock, and the angle of shearing <br />resistance of the denser, confined rock within the body of <br />loose dumped heaps almost certainly exceeds this. <br />Hoek and Bray (1977) indicate that the shear strength <br />behaviour of some waste dump materials can be non-linear, <br />with the apparent friction angle decreasing at higher normal <br />loads while the apparent cohesion increases. They suspect <br />this non-linearity will be exhibited ,by most waste materials <br />to a greater or lesser degree, their implication being that it <br />will be more pronounced in weaker materials. <br />In view of the absence of specific test data for the <br />waste rock material, shear strength parameters must be based <br />ceaeroQO eosw~n~, nre. <br />