Experimental Study On Shear Mechanical Properties And Acoustic Emission Characteristics Of Rock Joints Under Different Water Environments

The stability of jointed rock mass is often affected by the occurrence environment.Water is one of the most active factors affecting the safety of rock mass engineering in the environment.In order to study the shear mechanical properties of jointed rock mass under the action of water chemical corrosion,dry-wet circulation and seepage,based on the existing research,this paper takes irregular sandstone joints as the research object,and adopts the method of combining laboratory test and theoretical analysis to carry out the shear test and acoustic emission test of rock joints under the action of chemical solution immersion,dry-wet circulation and seepage.By comparing the shear test results of rock joints under natural state,the influence of chemical corrosion,dry-wet circulation and seepage on the shear mechanical properties and acoustic emission characteristics of rock joints is studied,and the peak shear strength model and shear deformation constitutive model of rock joints are established.The main research results are as follows :(1)Through the shear test of sandstone joints under different normal stresses,the shear mechanical properties of rock joints under natural conditions are studied.The results show that the overall peak shear strength,peak shear displacement and pre-peak shear stiffness increase with the increase of normal stress.The contribution of initial dilatancy angle to peak shear strength decreases with the increase of normal stress;the initial dilatancy angle is characterized by the contour area ratio of three-dimensional morphology parameters of joints.Combined with the analysis that the peak dilatancy angle is negatively correlated with the normal stress and positively correlated with the deformation resistance of the bulge,an empirical formula for the peak shear strength of rock joints is constructed,which is suitable for describing the shear failure modes of different types of rocks.(2)According to the shear stress-displacement curve shape characteristics of rock joints,it is divided into pre-peak compaction stage,linear stage,yield stage and post-peak softening stage.Based on the shear deformation characteristics of each stage of shear stress-displacement curve of rock joints,the constitutive model of shear deformation of rock joints is established by using piecewise function.Compared with the similar models,the newly proposed constitutive model of rock joint shear deformation has higher fitting accuracy for the test data,which better describes the whole shear stress-displacement curve of rock joints.(3)Acoustic emission characteristics can well reflect the evolution law of rock joint shear damage.The cumulative ringing count of acoustic emission parameters is used as the characteristic parameter to describe the joint shear damage characteristics.The joint shear damage constitutive model based on cumulative ringing count of acoustic emission parameters is established,and the rationality and correctness of the damage constitutive model are verified by experimental results.(4)The shear test results of sandstone joints under chemical immersion and wettingdrying cycles show that chemical corrosion and wetting-drying cycles have a deterioration effect on the shear mechanical properties of sandstone joints.Affected by chemical immersion and wetting-drying cycles,the pre-peak shear stiffness,peak shear strength and residual strength of sandstone joints decrease,and the peak shear displacement increases.In addition,a modified parameter reflecting the deterioration degree of rock joints is introduced to describe the deterioration of peak shear strength under dry-wet cycles,and a peak shear strength model of irregular rock joints under drywet cycles is proposed.(5)Through the shear tests of sandstone joints under different seepage pressures,the shear mechanical properties of rock joints under seepage conditions are studied,and the effects of seepage pressure,normal stress and joint roughness on the shear mechanical properties of rock joints are analyzed.The research results show that compared with the natural state without seepage,the rock joints show the characteristics of decreasing peak shear strength,increasing peak shear displacement and decreasing pre-peak shear stiffness under seepage.Based on the empirical formula of peak shear strength of rock joints proposed by Barton,combined with the effective stress principle and considering the influence of seepage water pressure on the basic friction angle,the peak shear strength model of irregular sandstone joints under seepage conditions is proposed.(6)The evolution law of elastic strain energy and dissipation energy in rock joint shear process under natural state,seepage state,chemical immersion and dry-wet cycle is analyzed from the perspective of energy,and the evolution mechanism of rock joint shear damage under different water environments is further revealed.The paper contains 121 figures,23 tables and 182 references.