Quantitative roughness profiling of fracture surfaces of a granitic host rock at a radioactive waste disposal site

摘要

The paper provides new results on the fracture surface roughness testing from the BátaapátirnNational Radioactive Waste Repository project. During the calibration of modeling and design work it wasrnnecessary to develop a simple and quantitative approach to predict the Joint Roughness Coefficient (JRC) valuernof fracture surfaces. To reach this goal laboratory-scale and on-site large scale surfaces were investigated. Thernroughness was studied on 15 smaller samples (average area of 73 cm~2), and on 5 larger in-situ granitic surfaces.rnThe latter were documented during the excavation of the repository chambers (average area of 12m~2). Additionalrnspecimens (more than 40) that were used for direct shear strength test (average area of 26 cm~2) were also studiedrnby generating 3D models with the software JointMetrix3D (JMX). In order to determine the shear strengthrnnumerically, the JRC value of the surface is one of the key influencing factors. The roughness parameter (R_p)rnand the roughness parameter of the surface (R_s) can be calculated using several 2D profiles of the surfaces tested.rnThe JRC values were calculated from the results of the shear strength test, and compared with the JRC valuesrncalculated from R_s. The resulting JRC values served as an input parameter to the original equation of Barton.rnFrom the evaluation of the relationship between JRC and Rs a new correlation were identified, which providedrna better estimation of the JRC values of the rock types tested. The following correlations were found:rnτ_b=σ_n tan(φ_b+(aln(R_S)+b)lon_(10)(JCS/σ)n)), where a=90.16 and b=1.39.The models were built in JointMetriX3D from the surfaces that were measured both in 2D (JMX profiling)rnand in 3D, with the OgreProject software. Unfortunately the 3D roughness profiling did not provide a reliablernapproximation therefore further studies are necessary in order to determine additional equations.