Angles of repose, angles of shearing resistance and angles of talus slopes

Recent arguments that the straight parts of talus slopes stand, in general, at angles less than the angle of repose of the talus material are considered in relation to different test procedures used in the measurement of the repose angle. Observations on coarse, well sorted, angular fragments showed no significant difference between the values for this angle determined in laboratory tilting-box tests and determined during outdoor cone build-up by rapid discrete particle rockfall. Measurements did indicate, however, that laboratory tests in which specimen size (in relation to particle size) is small produce steeper repose angles which are unrealistic in the field context. A detailed description is provided of process and form changes which occurred on large cones built up by stockpiling of crushed stone in a limestone quarry. These observations indicate that the processes of discrete particle rockfall and of avalanching of talus material may not be as independent of each other as previously suggested, and, together with the values of the repose angle of the cone material (35°), provide some support for the traditional view that talus slopes do, in fact, stand at or close to the repose angle of the talus material.