Study On Shear Characteristics Of Step Rock Joint

The shear mechanical properties of rock joint have an important influence on stability of rock structure.At present,most scholars have carried out a lot of research on shear characteristics of saw-tooth rock joint from undutant angle,shear rate and size effect.They have achieved some research results.As one of four typical rock joint in nature,the step type rock joint has less research on its shear characteristics.The research content is relatively simple,mostly concentrated on the aspect of high-to-length ratio.Based on multi-functional rock and soil contact damage test system and integrated mold for anatomical rock joint,more than 100 groups of rock specimens with different height-to-length ratios were produced for direct shear testing.The numerical direct shear test was performed using PFC numerical simulation software.The influence of shear rate,normal stress and rock joint size on failure mode and shear strength of rock joint was analyzed.The main work and conclusions are as follows:Firstly,the multi-functional rock and soil contact damage test system has been developed independently,which can be used to test velocity effect,stress effect and size effect.The test results are consistent with existing conclusions.Secondly,based on three design principles of integrated pouring,uniform stability of sample performance and rapid sample making,a rapid and integrated manufacturing mold of rock joint has been developed.It is not only simple in structure and convenient in disassembly,but also low in cost and easy to vibrate.Some step type rock joint specimens with height-to-length ratios of 0,0.1,0.2,0.4,and 0.6 were fabricated using this method,and corresponding direct shear tests were conducted.Thirdly,there are two main failure modes of step type rock joint,such as crush-cutting failure and shearing failure,which are influenced by height-to-length ratio,shear rate and normal stress in direct shear process.When height-to-length ratio,shear rate and normal stress are low,the failure mode of rock joint shows crush-cutting failure.In other cases,the failure mode is mostly shearing failure.Fourthly,for straight rock joint and step rock joint with failure mode of shearing failure,shear strength decreases gradually with increasing of shear rate,and the rate of change gradually decreases.Fifthly,shear strength of straight rock joint increases linearly with increasing of normal stress,and stress effect is not significant.Shear strength of step rock joint increases nonlinearly with increasing of normal stress,and growth rate gradually decreases.Therefore,shear strength of step rock joint has obvious stress effect characteristics.For large step rock joint,shear strength also has obvious stress effect characteristics.Sixthly,direct shear test of step rock joint with ratio 0.2 and different sizes was carried out.It is found that shear strength of step rock joint decreases with increasing of size,and has obvious size effect characteristics.Finally,the particle flow simulation software was used to establish a numerical model of step rock joint and subjected to direct shear tests under different normal stress.It was found that shear strength of rock joint increases nonlinearly with increasing of normal stress,and growth rate decreases gradually.The conclusion is basically consistent with laboratory test.