Study On Evolution Law Of The Sandstone Sliding Friction Characteristics

Open-pit coal mining has formed a large number of slopes.The slip surface inside the slope gradually penetrates and slides by loading perturbation.During the sliding process of the slope,the rock mass interface will gradually wear,which will weaken the sliding friction resistance,and make the sliding velocity increase continuously to cause the landslide disaster.In order to explore the evolution law of the sandstone sliding friction characteristics,a nonlinear characteristic test of the sandstone section sliding friction is carried out to establish the nonlinear function relationship between the amount of sliding surface wear and frictional resistance,and a sandstone sliding friction model is established.Combined with the discrete element particle flow numerical simulation and the sliding friction experimental results to analyse the sandstone sliding friction process,and then the evolution law of sandstone sliding friction characteristics is obtained,and the evolution mechanism of sandstone sliding friction is revealed.The research results are as follows:(1)A nonlinear friction coefficient model with effective contact area,wear quality and surface arithmetic mean height as variables is established.A sliding friction test device is developed to test the sliding friction nonlinear characteristics of the sandstone.The error analysis of the predicted value and the test value of friction coefficient found that when the wear difference coefficient c_w=2.0 and the mesh friction amplification coefficientβ=1.2,the minimum error is 5.72%.This verifies the rationality and accuracy of the friction coefficient model.(2)The nonlinear characteristic test of the sandstone sliding friction is carried out,and it is found that the sandstone sliding is the process of surface of asperities shearing off,being worn flat,new asperities shearing off,and the surface wear is accumulating continuously.The effective contact area,the wear quality and the arithmetic mean height of the worn surface change nonlinearly during the sliding process.When the sliding velocity of the sandstone increases,the wear mass decreases gradually,the increase rate of effective contact area slows down gradually,and the decrease trend of arithmetic mean height of wear surface slows down gradually.When the normal stress of the sandstone increases,the wear mass increases,the increase rate of effective contact area increases,and the arithmetic mean height of the wear surface decreases rapidly.(3)The numerical simulation analysis of the sandstone shearing process is carried out,and it is found that the shear stress exhibits a nonlinear trend of oscillating decrease,and the amplitude of the oscillation decreases gradually during the shearing process.When the normal stress and the undulating angle are small,the number of cracks is small,and the influence on the overall morphology of the specimen is small.With the increase of normal stress and undulating angle,the number of cracks increases rapidly,and the surface wear of the sandstone gradually exacerbates.It is proved that the sandstone shearing is a process of continuous accumulation of surface wear and continuous reduction of surface roughness.(4)To sum up,in the shearing process,sawtooth deformation-shearing-residual tooth deformation-shearing cycle continuously,and the wear gradually accumulates;in the sliding friction process,the surface asperities continue to wear,the effective contact area increases,the arithmetic mean height of the surface decreases continuously,and the friction coefficient decreases gradually.Therefore,the sandstone sliding friction is a process in which the asperity wears continuously and accumulates,resulting in a continuous decrease in the surface roughness and a continuous increase in the effective contact area,which eventually causes a decrease in the friction coefficient.The study on the evolution law of the sandstone sliding friction characteristics can provide a theoretical support for the analysis of the evolution process of landslide disasters and the research on the mechanism of wear and tear on the sliding interface of the slope.