Scale Effects in Rock Failure

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

With much of rock engineering involving large scale projects, the effects of scale - both spatial and temporal - on rock deformability and strength are central issues that are still not well understood. Joints and similar large-scale geological discontinuities are assumed to be the primary factor in reducing strength, but there is evidence to support the existence of a significant size effect even in "intact" rock. Recent developments in numerical modeling allow the interaction of fractures and the bridges of intact rock between them to be analyzed more realistically than in the past. The deep underground science and engineering laboratory (DUSEL) in Lead, South Dakota provides an excellent location to carry out fundamental research to evaluate and improve the numerical predictions. Large-scale in situ compression tests, in which pillars will be loaded to failure, are proposed for DUSEL Complete load-deformation curves will first be obtained in laboratory tests to assess the potential for brittle failure. Numerical predictions will be made of the pillar response to loading - using the Synthetic Rock Mass model - for all stages of pillar excavation. It is anticipated that the test specimens will range in diameter (or side width, if square) from about 2 m to 5 m, all with a final height to width ratio of 2:1. Knowledge transfer will be accomplished through a Grand Challenge, whereby research and consulting teams will be invited to submit blind predictions of the outcome of key stages of the in situ studies. This is intended to establish the state-of-the-art of predictive modeling, and to stimulate development. The educational mission will be to create and develop mechanisms and technologies that demonstrate, investigate, and enable the control of subsurface excavations through machine stiffness effects.