Application of the Elemental Degradation Approach to Problems in Rock Engineering

ABSTRACT: The brittle fracture of rock is a complicated progressive process caused by isolated microstructural changes. Modelling this process in the compressive stress regime is not straightforward, and precise engineering analysis and design therefore remains problematical. A new way of tackling the problem is through the recently developed local degradation approach, which has been developed as a means of using commercially available computational mechanics programs to model the process. Strength degradation and dilatancy are defined using degradation and dilatancy indices, which are determined from standard laboratory test results. Simplified elemental fracturing is used to introduce damage dependent permeability, and the Weibull distribution is used to introduce elemental heterogeneity of compressive strength. Together, these concepts allow realistic simulation of progressive breakdown of rock. The effectiveness of the approach is demonstrated by simulating laboratory uniaxial and triaxial tests. Models of mine support pillars show how width to height ratio affects their behaviour, and suggests that customary empirical design formulae may be overly conservative. For circular openings such as tunnels and wellbores, the degradation model produces detailed and realistic results showing the development and effect of progressive failure, as well as the influence of peripheral damage on the development of radial flow. Overall, the results suggest that application of the model will improve the effectiveness of engineering design.