The Assessment of the Overall Probability of Failure of Hard-rock Slopes Using the First Order Reliability Method and the Hunting Equation Method

The Assessment of the Overall Probability of Failure of Hard-rock Slopes Using the First Order Reliability Method and the Hunting Equation Method

Author: Charlie Harrison
Conference: GeoEdmonton 2018
Date: September 23-26, 2018

ABSTRACT
The overall probability of failure of a hard-rock slope is assessed using a combination of the First Order Reliability Method (FORM) and the Hunting Equation Method. FORM is used to assess the probability for each potential failure mode, which considers the correlation of the variables (e.g. discontinuity friction angle and cohesion). The overall probability of failure of the rock slope is then assessed using the Hunting Equation Method by combining every potential failure mode’s probability of failure.

The assessment outlined above is applied to a hard-rock slope that is not susceptible to rotational failure, which allows for the application of simple, closed form limit equilibrium methods for planar- and wedge-type failures in a spreadsheet. All the potential modes of failure for a slope, which could include multiple planar- and wedge -type failure mechanisms must be assessed individually. Consideration must also be given to multiple structural and geological domains within a slope, as the potential failure modes in each domain will need to be assessed and each domain may have a unique set of parameters that need to be assessed and correlated.

The author provides an example assessment of a typical rock slope located in the Coastal and Cascade Mountains, where hard rock slopes are in abundance. The potential failure modes are assessed, including the correlation of the variables. The overall probability of failure is assessed in the absence of rock support.

 

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