Abstract
The objective of this project is to utilize the Hoek-Brown Failure Criterion to estimate friction angle and cohesion of a rock mass. The California Geological Survey uses this data to delineate seismic hazard zones. Shear strength data typically comes from lab test results for foundation design or slope stability analyses, but the problem is that lab testing is expensive to conduct and often times this data is not available in geotechnical reports. When the California Geological Survey makes hazard zone maps without available shear test data, assumptions and generalizations have to be made about material strength and the Hoek-Brown Failure Criterion will determine if the current seismic hazard zoning efforts can be improved. The Hoek-Brown Failure Criterion is a method based on field observations and an evaluation of a rock’s lithology, structure and conditions of discontinuity. A field assessment of a rock outcrop produces three input parameters that can be plugged into a software program and friction angle and cohesion values are calculated.
The Hoek-Brown Failure Criterion is an alternative method that can reduce the amount of uncertainty in characterizing geologic unit strength and is a viable approach to mapping earthquake-induced landslide hazard zones on a regional basis when using an average friction angle, zero cohesion, unsaturated slope conditions, and susceptibility based on 5, 15, and 30 cm displacements.