ABSTRACT:

Stability analysis of weak rock slopes with daylighting bedding planes pose a challenge as a number of competing mechanisms of failure involving failure through the weak rock mass and sliding on the bedding plane are at play. A bedded weak rock slope was analyzed using limit equilibrium analysis and finite difference analysis with shear strength reduction method. The effect of long term cohesion degradation on slope stability was explored using perfectly-plastic and strain weakening models. Lower values of rock mass cohesion led to lower factors of safety and smaller zones of failure. Excluding the weak bedding plane from shear strength reduction resulted in a considerable increase in the critical shear strength reduction factor and a smaller zone of failure. The critical shear strength reduction factors from strain weakening models were in between those obtained from perfectly-plastic models using the peak and residual values of cohesion. This illustrates that stability of slopes in strain weakening materials can be dangerously overestimated assuming peak strength and unnecessarily underestimated using residual strength.

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