Geomechanical Evaluation of the Stability of Homogeneous Overburden Dump Slopes Based on Their Limiting Height

The stability of a homogeneous overburden dump depends on whether its height stays below a limiting value set by the strength of the dump material and by the bearing capacity of its foundation. This paper determines the limiting stable height of four homogeneous external dumps of the Kalmakir open pit (Almalyk MMC, Uzbekistan) for a rigid and for a weak foundation. The shear strength of the mixed-size dump rock was described as a function of the fine-fraction content, and design values were obtained with a safety factor of 1.2. For a rigid foundation the limiting height was calculated by three methods based on a circular slip surface: the G. L. Fisenko (VNIMI) method, the W. Fellenius method and the KarPTI method. For a weak foundation the limiting height was obtained from the critical load on the foundation soils and by the V. K. Tsvetkov method, for thawed (summer) and frozen (winter) soils. On a rigid foundation the limiting heights were 94.0–105.4 m, with mean values of 95.2–103.1 m, which exceed the present heights of 85–94 m by 1–21%. On a weak foundation the limiting height fell to 54 m when the soils were thawed and rose to 110 m when they were frozen. The bearing capacity of the foundation in the warm season is therefore the governing condition, and dumping on thawed soft soils should be limited to about 53–54 m.

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