| Based on the previous study on the water-rock interaction of the reservoir bank slope,the typical rock slope sandstone in the Three Gorges Reservoir area was selected as the research object,and the water-rock interaction test considering the fluctuation of water pressure and the immersion-air-drying cycle process was carried out.The study on the degradation effect and mechanism of the shear mechanical properties of single-joint rock masses under water-rock interactions has been carried out.(1)Direct shear tests under different normal stresses(0.5MPa?1.0MPa?1.5MPa?2.0MPa?2.5MPa)were carried out on single-joint rock masses,and the microscopic scanning of the joint surface was carried out before and after each direct shear test.On the basis of the previous characterization methods,combined with the scanning analysis of the three-dimensional topographic features of the joint surface,comprehensively considering the hierarchical structure characteristics of the joint surface,it is proposed to use the average undulation angle and the average relative undulation amplitude to characterize the first-order undulating structure,and the area expansion rate to characterize the secondary fine rough structure of joint surface.The correlation between the three-dimensional roughness coefficient of the joint surface and the morphological parameters is analyzed and established,and the error between the calculated shear strength of the joint surface and the experimental value is-3.318%?2.646%,which is in good agreement.The relevant research results can provide a good reference for the quantification analysis of the roughness of the joint surface and the estimation of the shear performance.(2)Repeated shear tests under different normal stresses(1.0MPa?1.5MPa?2.0MPa?2.5MPa)were carried out on single-joint rock masses,and the microscopic scanning of the joint surface was carried out before and after each direct shear test.The changes of shear strength,morphological parameters and consistency of jointed rock masses under repeated shearing are analyzed.The analysis results show that as the time of shearing increases,the shear strength,morphology parameters and joint matching coefficient of jointed rock masses decrease in an exponential function curve.After three repeated direct shears,the shear strength of the jointed rock mass,the morphological parameters and the joint matching coefficient of jointed rock masses tend to be stable.After four repeated direct shears,the shear strength decreased by 17.545%to 28.045%under various normal stresses,The area expansion rate,average undulation angle and average undulation amplitude decreased by21.187%?28.181%,8.523%?22.994%,4.713%?16.865%,and joint surface agreement decreased by 15.157%?32.746%.Finally,the joint roughness coefficient and joint matching coefficient of the joint surface are comprehensively considered,and the calculation formula of the shear strength under repeated shear is established by introducing the joint matching coefficient.(3)A 10-cycle water-rock interaction test was carried out to analyze the deterioration law of shear strength,internal friction angle,cohesion,joint roughness coefficient,and the joint matching coefficient of the joint surface of a single-joint rock mass under water-rock interaction.The analysis results show that with the increase of the water-rock cycle,the joint surface shear strength,joint roughness coefficient,and the joint matching coefficient of the joint surface of a single-joint rock mass all decrease in an exponential function curve,and the overall trend is"first steep and then slow".In the first 6 cycles of water-rock interaction,the shear strength,joint roughness coefficient,and the joint matching coefficient of jointed rock masses have deteriorated significantly,accounting for about 90%of the total deterioration.After 6 cycles of water-rock interaction,the deterioration trend gradually tends to be flat.At the same time,based on the revised shear strength of jointed rock masses,the internal friction angle and cohesion deterioration law of jointed rock masses under water-rock interaction is analyzed.In the first 6 cycles of water-rock interaction,they were decreased by 19.327%and22.636%respectively,and led to a large deterioration in the internal friction angle and cohesion parameters of the joint surface,accounting for about 90%of the total deterioration.Finally,the relationship between the shear characteristics and micro morphology of jointed rock mass under water-rock interaction is analyzed,and the joint roughness coefficient,joint matching coefficient,joint compression strength and basic friction angle of jointed rock mass under water-rock interaction are comprehensively considered.The shear strength degradation equation of jointed rock masses under water-rock interaction is established.(4)Through the analysis of the microscopic morphology characteristics under different water-rock interaction cycles,the change of immersion ion solubility,and the scanning results of electron microscope,the degradation mechanism of jointed rock masses under water-rock interaction is revealed.The analysis results show that the comprehensive results of the three types of effects of water mechanics,chemistry and physics lead to changes in the ionic solubility in the soaking solution,and at the same time the morphological characteristics of the joint surfaces change,the internal pores and cracks in the rock mass increase,and the overall structure tends to soften,which ultimately leads to a decrease in the shear mechanical properties of rock mass.In the first 6 cycles of water-rock interaction,the water-rock degradation effect was obvious.The plasma solubility of Ca2+?K+?Na+in the immersion solution increased by 16.313%,28.357%,and 32.535%,respectively.Among them,the increase of K+solubility accounts for 89.327%of the entire water-rock cycle.At the same time,the energy spectrum analysis results show that the decrease of the chemical element K content in the rock sample accounts for 87.461%of the entire water-rock cycle,the decrease of joint surface roughness coefficient accounts for 87.480%of the entire water-rock cycle,and the reduction in shear strength accounts for about 90%of the entire water-rock cycle,which shows good coordination.After 6 cycles of water-rock interaction,the changes in the solubility of each ion in the immersion solution tended to be stable,the morphological characteristics of the joint surface remained basically unchanged,and the shear strength of the jointed rock mass also gradually stabilized.(5)Based on the direct shear test results under different water-rock cycles,and according to the characteristics of the shear stress-shear displacement curve.The Clough-Duncan hyperbolic model was used to establish the shear constitutive model of jointed rock mass under water-rock interaction without considering repeated shear damage and the shear constitutive model considering repeated shear damage correction,and respectively carried out verification analysis.The analysis results show that the shear stress-shear displacement curve calculated by the Clough-Duncan hyperbolic model is in good agreement with the test curve,which can more accurately simulate the shear stress-shear displacement curve of jointed rock mass under water-rock interaction.So as to provide corresponding theoretical basis for slope engineering stability research. |
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