Frictional Sliding Behavior And Instability Process Of Granite Under Constant Displacement Loading

Contact surface frictional instability is an important phenomenon in actual engineering and nature,such as fault instability sliding and landslide instability sliding.The release of energy from the crustal to drive fault slip and failure is an important mechanism for earthquakes.In the laboratory,the friction of the rock friction surface is usually driven by controlling the monotonically increasing displacement of the loading point to study the fault sliding behavior and its periodic stick-slip instability.However,fault loading in the actual crust is often very slow,much slower than laboratory loading rates.An important effect of friction is the healing of frictional strength,which means that the frictional strength will increase with contact time.Previous theoretical models and experiments have mainly focused on the problem of rock friction instability under monotonic control of displacement.Therefore,under extremely low speed loading,will friction instability occur in the rock? What is the sliding behavior if frictional instability occurs? It has become a basic core problem in understanding the earthquake mechanism and its prediction.Based on this,this paper conducts experimental research and observations on the friction characteristics of granite under extreme low speed-constant displacement(zero speed)loading.A high-precision double-shear test loading and testing system for granite was built,and the displacement,load and sliding displacement of the loading point in the double-shear friction test were directly monitored.A comprehensive observation of the friction behavior of granite under constant displacement loading is achieved.Experiments have obtained a complete sliding spectrum from traditional stress relaxation,slow slip(earthquake)to fast instability.The friction characteristics of granite under different stress levels and constant displacement loading were systematically observed,and the various frictional habits exhibited by the friction of granite during multiple cycles of loading were obtained.By changing the lateral pressure,the friction behavior of energy release driven by granite under constant displacement loading under different positive pressures was studied.The statistical analysis of the frictional instability stress drop of granite under two loadingmodes of constant displacement loading and monotonically increasing displacement was carried out.The characteristics of the precursors of frictional instability are analyzed,and the experimental observations show the stress anomalies before sliding.The friction and sliding process of granite driven by energy release under constant displacement loading is analyzed in detail.It is shown that there is a linear relationship between the sliding friction force and the sliding displacement in this process,which is obviously different from the non-linear process in the loading process that monotonically increases the control displacement,corresponding to a different instability mechanism.