The paper provides summaries of recent developments on rock joint roughness, rock joint strength and deformability, and rock mass strength and deformability based on six journal papers the author published recently with his graduate and undergraduate st
Accurate quantification of roughness is important in modeling hydro-mechanical behavior of rock joints. Roughness of natural rock joints was measured using a laser profilometer (Fig. 1). A typical rock joint surface used for the study is shown in Fig. 2. A highly refined variogram technique [1] was used to investigate possible existence of anisotropy in natural rock joint roughness [2]. Investigated natural rock joints showed randomly varying roughness anisotropy with the direction (Fig. 3). A scale dependant fractal parameter, Kv, seems to play a prominent role than the fractal dimension, Dr1d, with respect to quantification of roughness of natural rock joints [2]. The parameter Dr1d×Kv seems to capture the overall roughness characteristics of natural rock joints well [2]. The one-dimensional modified divider technique was extended to two dimensions to quantify the two-dimensional roughness of rock joints [2]. The developed technique was validated by applying to a generated fractional Brownian surface with fractal dimension equal to 2.5 (Fig. 4 and [2]). It was found that the calculated fractal parameters quantify the rock joint roughness well (Table 1 and [2]). A new technique is introduced to study the effect of scale on two-dimensional roughness variability and anisotropy [2]. The roughness anisotropy and variability reduced with increasing scale (Figs. 5 & 6 and [2]).
Roughness of a natural rock joint was measured in different directions using a laser profilometer [3]. Fractal based two stationary roughness parameters and a non-stationary roughness parameter are used to quantify anisotropic roughness [3]. A plaster of Paris based model material was used to make model material replicas of the natural rock joint (Fig. 7). Direct shear tests were performed at five different normal stresses, in each of the directions that were used for the roughness measurements, to measure the anisotropic peak shear strength of the model joint. Required observations and experiments were conducted to estimate the following:
the asperity shear area as a proportion of the total surface area of the joint;
the basic friction angle of the model material joint; and
the joint compressive strength and to develop a new peak shear strength criterion for the model material joint [3]. Part of the direct shear test data was used to develop the new peak shear strength criterion given through Eqs. (12) & (5) in [3]. The other part of the data was used for model validation. Measured and predicted peak shear strengths of the model joint for different normal stresses in different directions are shown in Fig. 8.
