Abstract:

Discontinuities with different rock types are widely distributed on the Three Gorges reservoir area of Yangtze River, and the study of their peak shear strengths can provide a theoretical basis for the stability analysis and evaluation of rock masses. Three groups of rock-like specimens with different surface morphologies and upper and lower joint wall strengths were cast by high-strength gypsum, and then directly sheared under different constant normal stresses. The joint wall strength combination coefficient (λ ) is introduced to quantify the comprehensive influence of the compressive strength and basic friction angle of the discontinuity wall on the peak shear strength of discontinuities with different joint wall strengths. The smaller λ is, the greater the strength difference between the upper and lower discontinuity wall is. The peak shear strength of rock discontinuities with different joint wall strengths increases non-linearly with increasing λ , which is more significant at higher normal stress. Based on Barton criterion, an empirical criterion for estimating the peak shear strength of discontinuities with different joint wall strengths has been established by multiple regression analysis. The new criterion is further verified by the direct shear test results of the natural and artificial tooth-shaped discontinuities with different joint wall strengths, and tested shear strengths are in good agreement with predicted values by the new criterion. The application of the new criterion in the stability evaluation of soft and hard inter-bedded rock slopes is briefly analyzed. Finally, the applicability of Wu’s equation and the advantages and disadvantages of the new criterion are discussed.

Key words: rock discontinuity with different joint wall strengths, shear strength criterion, joint wall strength combination coefficient