Quantifying topography and closure deformation of rock joints

This paper presents a study for quantifying both the joint topography characteristics and the load-closure deformation of a rock joint under normal compressive loading condition. The study covers (1) laboratory measurements of rock joint surface profiles using a profilometer designed and fabricated by the research team, (2) development of a mathematical method to identify the waviness and unevenness components in joint surface profiles and the associated composite topography, (3) development of a general load-closure deformation model by using both the waviness and unevenness components in the composite topography, (4) unconfined compressive testing of rock samples with joints for the experimental load-closure deformation of joints and, (5) verification of the general load-closure deformation model by the experimental load-closure deformation results. The study leads to the following four findings: (a) the mathematical method can be used to identify the waviness and unevenness components for joint surface profiles and its composite topography. The height characteristic parameters of the complete surface topography of a joint are mainly determined by the waviness component. The texture characteristic parameters of the complete surface topography of a joint are mainly determined by the unevenness component, (b) joints can be classified into the three contact state cases using the waviness and unevenness components for both the joint surface profiles and the associated composite topography. The load-closure deformation behavior of a joint is determined by the waviness and unevenness components of the composite topography for a specific contact state, (c) the general load-closure deformation model developed in this paper is applicable to the three contact state cases. The general load-closure deformation model uses the composite topography of a joint and can take into account the effects of the contact states, the initial aperture and the waviness and unevenness components; (d) parametric studies and verifications with the uniaxial compression test results show that the general load-closure deformation model gives reasonable estimations of the load-closure deformation behavior of rock joint under compressive loading and can be reduced to those given by other researchers in the relevant literature.