Experimental Research On Microscopic Shear Failure Mechanism Of Rock Under Water Chemical Solution Etching

The rock engineering not only by the load, but also by water erosion of the thechemical solution in their environment during the operation period.The cumulativeeffect of water-chemical solution etching frequently make rock mineral composition,structure and mechanical properties change, pose a threat to the long-term stability ofthe rock engineering.Therefore,aimed at rock and soil easily happened shear failureduring the rock engineering and the degradation of the mechanical properties of thesandstone in the water-chemical environment,the sandstone obtained from the ThreeGorges Reservoir(T3xj) under water-chemical solution etching are studied on thecharacteristic of the development process of mesoscopic crack and acoustic emissionunder shear loading by the independent development of meso-shear test equipment forcoal rock and PCI–2acoustic emission detection analysis system.Simultaneously，it isalso researched on temporal and spatial evolution law of crack and acoustic emissioncharacteristics of sandstone under different etching solutions, different etching time andthe different normal stresses in shear loading. The main results obtained are as follows:(1) The surface crack of sandstone appeared before the shear stress peak underdifferent etching solutions, with the increasing of water chemical solution etching, theshear strength of sandstone reduced, the final destruction crack width increased,deviation angle of predetermined shear plane and secondary cracks also increased. Thepeak value of acoustic emission events rate always appeared lag the time of the shearstress reached its peak, and the lag difference decreased with the increasing of erosiondegree.(2) The evolutionary process of surface crack of sandstone at different etching timeunder pH values of water chemical solution at5and12are consistent.The surface crackwas observed frist in the upper or the lower end portion of specimen. Furthermore,withthe increasing of etching time, the erosion degree and the deformation of sandstoneincreased,the shear strength reduced,and the width of the crack and secondary cracksincreased.But the crack fracture morphology of sandstone under acidic conditions aremore complex than that under alkaline conditions.The acoustic emission signal ofsandstone etched by the the water chemical solution on different time are rarely beforethe shear stress reached peak,wherers increased during the shear stress peak to the maindamage occurred period. (3) The shear deformation of sandstone under different normal stress have severaldistinct stages, and the shear stress are equal to the normal stress at the obviousseparation between the pore-fracture compaction stage and elastic deformation stage.With the increasing of normal stress, the shear strength increased, but deviation angle ofpredetermined shear plane also decreased when final damaged. Specimen often occoursfailure after the peak shear stress maintained a period.There is an obvious timedifference between the AE event rate and shear stress reached peak.The cumulative AEevents after the final destruction are most with the increasing of normal stress.