Tensile Strength And Splitting Failure Mechanism Of Rock With Eccentric Fracture

The tensile strength of rock is much lower than its compressive strength.However,the random distribution of pore cracks and other defects in natural rock body will significantly affect the strength and failure characteristics of rock body.Therefore,the study of tensile strength and failure characteristics of rock with eccentric fractures is of great significance to the stability of rock mass engineering.In this paper,we carried out platform Brazilian splitting test,VIC-3D test,and acoustic emission test on rocks with cracks.We analyzed the influence of eccentricity and crack dip angle on tensile strength,macroscopic splitting failure characteristics,and microscopic damage evolution characteristics of specimens.Based on the existing Brazilian splitting theory and the obtained test results,the peak load prediction model of rock samples with eccentric cracks was established.Based on the damage theory and COMSOL numerical software,the splitting failure process of specimens was reproduced.The effects of eccentric distance,crack dip angle,position,and number of cracks on the strength and splitting failure are studied,and the splitting failure mechanism of eccentric fractured rock was revealed.The main conclusions are as follows:(1)The variation trends of load-displacement curves of specimens are similar under different eccentric distance and crack dip angle,with compaction stage,elastic stage,stable crack growth stage,and unstable crack growth stage.The prefabricated cracks weaken the strength of the specimen,and the strength of the specimen is affected by the eccentricity and crack dip angle of the cracks.The peak load of the sample under different eccentric distances shows different variation laws with the increase of crack dip angle.With the increase of the eccentric distance,the peak load of the specimen shows a trend of increasing gradually.(2)When the crack dip angle is constant and the eccentric distance r is 0 mm and 5 mm,the cracks caused by the failure of the sample mainly propagate from the prefabricated crack tip to the loading end.When the eccentric distance r is 10 mm,the crack propagates along the loading axis.When the eccentric distance is constant and the crack dip angle α is 30°-90°,the splitting failure process of the sample changes obviously,and the failure mode is similar.Vertical splitting cracks are caused by tensile stress,while horizontal splitting cracks are mainly caused by compressive stress.The crack dip angle has no obvious effect on the acoustic emission characteristics of the sample.When r is 0 mm,i.e.no eccentric distance,the ringing count of acoustic emission presents a concentrated distribution pattern.When the crack has eccentric distance,the acoustic emission ringing count presents uniform distribution.(3)Based on the test results and combined with the theoretical formula of the tensile strength of the complete Brazilian disc with the platform,we established a peak load prediction model for rock samples with different fracture inclinations when the eccentric distance is constant.On this basis,the peak load prediction model of rock samples is established under the coupling of two factors fracture eccentric distance and crack dip angle.The correctness and rationality of the prediction model are proved by comparing with the additional test results.(4)Based on the damage theory and COMSOL numerical software,a numerical model for splitting test of specimens with cracks was established,and the numerical results were compared with the test results to verify the rationality of the numerical model.When the crack is in the horizontal direction,as the eccentric distance increases,the effect of the crack on the failure of the specimen is smaller,and the peak load shows an increasing trend.When the crack is on the loading axis,as the eccentric distance increases,the damage of the crack on the specimen increases,while the peak load shows a decreasing trend.The closer the crack is to the loading axis,the more significant the impact on the failure of the specimen,and the smaller the peak load.When the specimen contains double cracks,the crack dip angle of the crack has little effect on the failure mode of the specimen,but the peak load decreases first and then increases with the increase of the crack dip angle.When the double cracks are in the horizontal direction,as the eccentric distance increases,the influence on the failure of the specimen is smaller,but the peak load increases gradually.