Empirical Shear Strength Criterion for Rock Joints Based on Joint Surface Degradation Characteristics During Shearing

The shear strength of the rock discontinuities under different shear rates is of great importance to evaluate the stability of rock mass engineering, which is remarkably influenced by the size effects induced by both the length and the undulated amplitude of discontinuities. An advanced shear strength criterion taking into account the size and the shear rate simultaneously was proposed. There is an advantage of the dimension unity in terms of the new shear strength criterion in comparison to previous related empirical equations. Additionally, it can be degraded into the International Society for Rock Mechanics (ISRM)-suggested Barton shear strength empirical equation on the peak shear strength of the rock discontinuities. Then, based on a new dynamic direct shear testing device on rock joints, the granite discontinuities with various lengths (200 mm to 1000 mm) and undulated amplitudes (3 mm to 23 mm) were designed to conduct direct shear tests under different low shear rates (0 mm/s to 1 mm/s) to verify the involved empirical equations. It was found that the results predicted by the new shear strength criterion agreed well with the experimental results. It was proved that the new shear strength criterion had a better applicability to characterize the shear strength of the rock discontinuities.

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Research on Peak Shear Strength Criterion of Rock Joints Based on the Evolution of Dilation Angle

10.21203/rs.3.rs-287610/v1 ◽

2021 ◽

Author(s):

Linnan Ding ◽

Guoying Li

Keyword(s):

Shear Strength ◽

Normal Stress ◽

Test Data ◽

Roughness Parameter ◽

Strength Criterion ◽

Rock Joints ◽

Peak Shear Strength ◽

Shear Strength Criterion ◽

Dilation Angle ◽

New Criterion

Abstract The surface morphology of joints directly determines the contact area and peak shear strength of rock in shearing. This research gives a detailed description of the three-dimensional roughness parameters proposed by Grasselli, and discusses the morphology characteristics of the roughness parameter C in different ranges. Quoting Xia's direct shear test data, the relationship of peak shear strength, peak shear strength/normal stress, residual strength, dilation with roughness and normal stress are studied. The deficiencies in the previous classical criteria are explained in detail. A new peak shear strength criterion is established based on the boundary conditions of the dilation angle. The nonlinear characteristic of peak shear strength is included in the peak dilation angel, so that the new criterion satisfies the Mohr-Coulomb law of nonlinear form. In the expression of the initial dilation angle, the new criterion satisfies the fact that the peak shear strength decreases after once sheared. Finally, the test data of Grasselli and Yang are used to compare the prediction accuracy of Grasselli’s criterion, Yang’s criterion, Xia’s criterion and the new criterion. In general, the new criterion has the highest degree of agreement with the test results.

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