| dc.description.abstract | The mechanical strength of the rock mass is affected by the joint surface structure and the joint surface roughness coefficient (JRC). Barton (1977) proposed an empirical chart to estimate the JRC by visual classification, but this method seems subjective. In recent years, many researchers have proposed using analytical methods to evaluate JRC more objectively. To better understand the relationship between the roughness of the joint surface and the JRC value, prior researchers in our group collected and digitized 136 rock joint profiles and performed statistical analysis on the standard deviation of the profile elevation difference. As a result, a relationship between the standard deviation and JRC profile height difference was proposed and proved valid.
In this study, the joint profiles of JRC=3, JRC=10, and JRC=19.6 were randomly generated by the proposed equation, and the cast model was printed using 3D printing technology.In addition, a large amount of artificial gypsum soft rock specimens was prepared by pouring the material into the model. We used these artificial soft rock jointed specimens to perform the following tasks: (1) Use the existing JRC estimation methods to verify the jointed specimen with the specified JRC values. (2) Carry out the direct shear tests under the normal stresses of 0.5MPa, 1.0MPa, and 2.0MPa.
The research results showed that: (1) the actual JRC of the artificial soft rock joint surface after curing is much smaller than that of the specified JRC (2) the peak shear strength estimated by the Barton empirical formula and the direct shear test is comparable. The percentage difference is within 20%. (3) The failure area ratio of the specimen after shearing is positively correlated with the normal stress, and the JRC of the specimen does not affect the failure area ratio. (4) The roughness of the low-JRC specimen is higher after shearing, and the roughness of the high-JRC specimen is reduced after shearing.
This study also uses PFC software to simulate artificial soft rock for uniaxial compression and direct shear tests to analyze the micromechanical behavior. In addition, the physical uniaxial compression test was used to verify the numerical parameters in the PFC model, and the direct shear simulation was carried out with these parameters.
The numerical simulation results show that: (1) The results obtained from the uniaxial compression simulation are highly consistent with the physical experiments. (2) The direct shear simulation was first carried out using the verified parameters by a uniaxial compression test. As a result, the peak shear stress and stiffness of the simulation results are much larger than those of the physical experiment, and the failure conditions of the specimen are also inconsistent with the physical experiment. (3) The numerical parameters were modified to improve the simulation, as mentioned in earlier results. The peak shear stress and stiffness of the direct shear simulation are roughly in line with the physical experiments. | en_US |