Experimental study on size effect of shear strength of rock joints
Size effect of shear strength of rock joints has become the consensus of academic and engineering circles,but the existing theoretical and numerical studies show that the shear strength of rock joints may have positive size effect,negative size effect or no size effect.Due to the difficulty,high cost and long period of size effect test of shear strength of rock joints,there are few direct shear tests of joints with series size,especially for full-coverage direct shear test of rock joints with fluctuation morphology in a series of sizes(100-600 mm).In this paper,based on Barton's typical morphology curves,16 sets of multi-scale joint samples were made by multi-scale joint integration mold.The direct shear test of a series of multi-scale joints with full coverage of fluctuation morphology was carried out through the self-developed shear strength size effect test system of rock joints,and non-contact dynamic deformation measurement of the whole test process was carried out by DIC.The results show that:(1)Upper asymptote of peak shear strength of rock joint exhibits a negative size effect law,and lower asymptote exhibits a positive size effect law.The specific pattern of size effect is related to the sampling position and fluctuation morphology characteristics.(2)Different shear failure modes such as shear,climbing and coupling will occur in the same morphology of rock joints with different sizes.The shear failure modes of joints with different morphology characteristics of the same size samples are also different,and the larger the fluctuation degree of surface morphology,the faster the strain growth.(3)The larger the size,the more obvious the peak characteristics of shear stress and shear displacement curves of rock joint with large fluctuation morphology;the smaller the size,the larger the discreteness of peak shear strength of rock joint with large fluctuation morphology.(4)Based on the equal weight coefficient method,peak shear strength evaluation of large-scale rock joint is carried out.The weighted evaluation value of peak shear strength calculated by Grasselli formula has a large error compared with the measured value.
rock mechanicsrock jointshear strengthsize effectdirect shear testfluctuation morphology
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