Modeling Drift Stability in Fractured Rock Mass at Yucca Mountain, Nevada - Discontinuum Approach

ABSTRACT: The rock mass of the proposed geological repository for high-level radioactive waste at Yucca Mountain (YM), Nevada, is highly fractured and the fracture network is both irregular and complex. Consequently, a discontinuum approach is often used to model the stability of emplacement drifts, and fracture patterns are often largely simplified. This paper identifies important factors and limitations in modeling drift stability at YM using a discontinuum approach, particularly when a simplified model is used. Results show (i) fracture patterns have significant effects on simulated rockfall, fracture displacement, and ground support performance; (ii) for a given fracture pattern, the combination of thermal expansion coefficient and rock block and fracture mechanical properties determines the simulated rock block deformation and fracture displacement; (iii) most commonly used techniques for reducing problem size do not have significant effects on rock block and fracture behavior in the immediate vicinity of the drifts; and (iv) duration and frequency content of input ground motion do not show significant effects on drift stability unless extensive failure exists prior to dynamic load.