INFLUENCE OF INTERNAL WATER AND MATERIAL PROPERTIES ON MINE DUMP STABILITY

Assessing the internal strength of mine rock waste dumps is somewhat difficult and occasionally challenging as a result of material variability, mode of placement, internal moisture conditions, and possibly the "lack" of an adequate engineering design particularly for dumps constructed ten or more years ago. Normal types of instabilities encompass "sliver" failures and settlement or cracking of the dump but these failures are rarely catastrophic. Two particular types of waste dump failures will be discussed which produced large volume failures and were analyzed based on failure morphology, strength testing and what it may indicate about the failure process, material behavior, degree of dump saturation and dump design.

The first failure was from a 200 foot high dump constructed at the angle of repose which failed disastrously producing a large debris flow traveling horizontally for over 500 feet. Based on strength testing and geometry the failure required the development of pore pressures which were initially difficult to understand given the free draining dump material. The second failure was a large scale rotational instability of an engineered dump with a slope face between 20 to 30 degrees and approximately 350 to 400 feet in height. This waste rock dump constructed in stages between 10 and 20 years failed unexpectedly the cause of which may be related to material strength and dump construction practices.