Study On Microscopic Contact And Friction Mechanical Properties Of Fault In Variable Speed Slip Process

In the process of underground mining,many engineering disasters has occurred due to slip and instability along faults.At the same time,fault slip is also affected by the microscopic contact of the fault surface.Therefore,the study on the microscopic contact and friction mechanics characteristics during the variable-speed sliding of faults is very important in geological disaster prevention,early warning,seismic mechanism exploration and prediction.At present,many regularity summaries based on experiments have been used to qualitatively describe the variable-speed slip process of faults,but their application has great limitations.In order to quantitatively describe the variable-speed slip process of the fault,it is necessary to establish a microscopic physical friction model.Based on this,combined with the wear theory and accurate characterization of the fault surface,a characteristic displacement solution model was established to describe the fault slip process more accurately.The main research contents and conclusions of this article are as follows:(1)Analyze the friction constitutive model deeply.A comparative analysis of the two velocity-state friction constitutive models shows that the two models are consistent in describing the transient changes of the friction coefficient,and there are great differences in describing the exponential decay part.The constitutive equation of the sliding law is more adaptable.Based on this constitutive equation,this article explores a method to explain each parameter in the model.(2)Establish the characteristic displacement solution model to characterize the key parameter₍(8) in the process of fault variable-speed slip accurately.The finite element analysis software ANSYS was used to verify the hypothesis in a single micro-contact contact model,and the relative error was within 10%,which proved its feasibility.This paper established a single micro-contact model by considering the influence of elastic deformation,surrounding micro-contact,plastic deformation,and creep deformation,and characterizes the total volume change of a single micro-contact during the sliding process,then use statistical methods to describe the volume change of all micro-contacts on the contact surface during the variable speed slip.Based on this,combined with the classic wear theory,considering the influence of friction work during the slip process,a characteristic displacement solution model was constructed to analyze the friction characteristics during the fault variable speed slip process quantitatively.(3)Verify the characteristic displacement solution model by variable speed slip experiment.Through experiments to explore the characteristic displacement and volume change of the rock during variable-speed sliding under different loads and the micro-contact radius R of different surfaces,it is found that the characteristic displacement value and volume change value are positively correlated with the micro-contact radius and load.The characteristic displacement value obtained by the experiment was compared with the result obtained by the model.The result shows that the error between the experimental value and the model value was within 20%,which also proved the rationality and validity of the characteristic displacement solution model.In addiction,it is observed that during the process of variable-speed sliding of the rock,the increase in speed has a greater impact on the surface than the decrease in speed.At the same time,there are obvious shear bands in the sample after shearing.