Study On Frictional Sliding Characteristics Of Rock Under Hydro-Chemical Conditions

Discontinuous structural planes such as joints and fissures widely exist in the rock mass.The fissures are the weak planes in the rock mass.Sliding along the fissures is the main form of movement after rock fracture,and is also the inducement of various geological disasters.The existence of water in the fracture surface is often the main cause of geological disasters.The water-mechanical-chemical coupling has transformed the structure of rock fracture surface and affected the rock friction sliding mode.This paper explores the frictional sliding characteristics of small-sized sandstones,limestones and basalts under different hydro-chemical conditions,including the magnitude of frictional strength and its velocity-dependent and time-dependent frictional sliding properties through velocity-step tests and sliding-control-sliding tests,combined with the analysis of the microstructural changes of the fracture surfaces before and after the tests.The main studies and results are as follows:(1)The frictional strength of fissures in sandstone,limestone and basalt are all maximum when they are not soaked,and the frictional strength increases with increasing p H of the water chemical solution,and increases with decreasing soaking time,gradually approaching the frictional strength of unsoaked rocks;at the same time,the frictional strength remains constant with increasing positive stress.(2)The three rock fractures of sandstone,limestone and basalt exhibit velocity enhancement in the range of 1～3 MPa positive stress,4～6 immersion solution p H,0～120 h immersion time and 1～30 μm/s sliding velocity,with the velocity dependence decreasing with decreasing water chemical solution p H and increasing immersion time,and increasing with increasing positive stress.(3)The reduction in frictional strength and healing of fractures in sandstone,limestone and basalt all increase with increasing control time and are linearly related to the logarithm of the control time;they also all decrease with increasing positive stress,indicating that the increase in positive stress inhibits creep slip of fractures to some extent(within the control phase).(4)The amount of frictional strength reduction and healing of rock fractures decreases with decreasing soak p H and increasing soak time for the same positive stress and control duration,and unsoaked rock fractures have higher frictional strength healing values and healing rates and are more stable in the control phase than under water chemical action conditions.(5)The carbonate content of the three rocks is in the order of limestone >sandstone > basalt,and the degree of influence of water chemistry on the friction strength,velocity dependence and time dependence of the three rocks is in the order of limestone,sandstone and basalt.The microstructural analysis was attributed to the dissolution of calcite due to exposure of the rock fractures to acidic solutions creating new void spaces,removing calcite cement from the rock matrix and ultimately reducing the pre-consolidation strength of the fracture surfaces.During the initial compression of the sample in the shear device,the alteration surface of the acid-reacted sample collapses and fills the fracture with fine particles.This prevented the formation of micro-bumping and effectively created sliding planes.