Abstracts Category : Other

Influence of test conditions on post-peak deformation behavior of rock

by Yuhang Xu

Understanding the post-peak deformation behavior of rock is important for underground rockengineering. Laboratory property testing is commonly employed to investigate the post-peakdeformation behavior. However, the test conditions of laboratory testing, especially the LoadingSystem Stiffness (LSS) of stiff test machines, are usually varied and the influence of thisvariation on the test results has not been fully elucidated. In addition, studying the influence oftest conditions on the post-peak deformation behavior of rock is crucial for interpreting testresults and subsequently applying the results to rock engineering design. The goal of this dissertation is to identify how the post-peak deformation behavior of a rockspecimen is affected by three major aspects of test conditionsthe specimen geometry, thecontact conditions, and the LSS. To achieve this goal, an FEM/Explicit tool was employed tocarry out numerical experiments, in which the same material property was assumed for the rockspecimens and each wanted test condition was isolated for analysis. The well-observed slenderness effect and the recently-observed cross-sectional shape effect onthe Uniaxial Compressive Strength (UCS) of rocks were studied. The modeling results suggestthat the numerical tool and models are suitable for investigating the problem and the hooptension theory could be flawed. Next, the cross-sectional shape effect on the post-peakdeformation behavior was investigated. The modeling results reveal that although the influenceof the cross-sectional shape on the UCS of rocks is small, the cross-sectional shape affects thepost-peak deformation behavior considerably. The actual contact condition and the end effect in true triaxial compression tests were simulated while the legitimate intermediate principal stress (2) effect was excluded from the rock material contacts are frictional and the specimen in the 2 loading direction is squat. Thus, existing 3Dempirical failure criteria based on previous true triaxial compression test results mayoverestimate the rock strength.The influence of LSS on the post-peak stressstrain relations of stable rock failure was examined.Key loading components of stiff test machines were considered in the numerical model. Themodeling results clarify that LSS affects the post-peak stressstrain curves of rocks even whenthe failure process is stable. Unless LSS is either perfectly rigid or equivalent to the critical LSS(), the post-peak stressstrain curves obtained under various LSS (with LSS > ) are varied andall steeper than the one under an ideal loading condition. This dissertation demonstrates the cross-sectional shape effect in the post-peak deformation stage,the long overlooked 2 effect caused by the end effect, and the variation of post-peak stressstrain curves due to the LSS. This dissertation also makes a contribution to examining the hooptension theory and recognizing the correct choice of cross-sectional shape for test specimens,offers