Joint behaviour during shear process using an innovative equivalent geometrical and 3D printing technology

Abstract The morphology of rock joints has been recognized as the key factor controlling its mechanical behavior, including its pre-peak and post peak phases. It is playing a significant role in joint aperture in association with asperities crushing, and rock matrix yielding deformation. The purpose of the paper is to examine how the joint aperture or closure occur in the joint, discussing the relationship with normal stress, joint morphology and intact matrix mechanical properties. To do this, an innovative methodology based on 3DP technology using a sand and phenolic binder was applied to construct the matrix and joint. The surface roughness was considered to have fractal properties with a self–affine replication, in accordance with natural observations. The constructed joint underwent eighteen shear tests with constant normal stress. Preliminary results revealed that, for each of pre-peak and post-peak phases, the joint behavior was controlled by a specific range of asperities sizes. Three behaviors were observed depending on the applied normal stress: (i) at low normal stress the waviness causes dilation; (ii) at normal stress over 40% of the UCS value, tensile and/or slip cracks are observed around the waviness, led to a crushing and beheading of these asperities; (iii) at intermediate normal stress, the two mechanisms were conjointly observed.