Experimental Study On Evolution Characteristics Of Rock Uniaxial Compression Damage Under High Water Pressure

The pore distribution,structural strength,acoustic emission,infrared radiation and temperature of limestone will be changed under the action of permeable water pressure,which significantly affects its engineering application.Meanwhile,the study of mechanical properties and damage-instability prediction of limestone in high osmotic water pressure environment has become an important and difficult problem.Focusing on the failure mechanism and prediction of limestone under the high pressure osmotic water environment,with the help of a variety of monitoring instruments,studying the effect of meso-structure changes of limestone under the action of osmotic water on its macroscopic mechanical properties based on the comprehensively analysis of the collected information.Then the failure mechanism of limestone is further analyzed and the damage evolution model of limestone considering the action of osmotic water pressure is established and verified.(1)Under the action of different water pressure,the experiments of saturated water test,mass and wave velocity test,X-diffraction test,SEM test,acoustic emission characteristics acquisition test were carried out on the limestone samples respectively to study the micro,meso and macro phenomena change rules.and the results show that the changes of microstructure and mesostructure have significant effects on the macroscopic mechanical properties.(2)The mechanical properties,acoustic emission characteristics of limestone were analyzed through rock uniaxial compression test under the action of single osmotic water and the combined action of axial pressure and osmotic water pressure respectively.It is found that the stress-strain curve of limestone presents a four-stage change rule under the action of different osmotic water pressure.As the osmotic water pressure increases,the ultimate strain in the compaction stage gradually increases,and the elastic modulus and peak stress of rock samples decrease;The acoustic emission ringing count and energy active phase tend to small stress gradually,and the cumulative value increases gradually.Under the combined action of axial pressure and osmotic water pressure,with the increase of axial pressure,the stress,fracture and acoustic emission parameters of the rock sample show a similar change rule.However,under the action of axial pressure,the water-rock erosion in the rock sample is more obvious and the mass loss is greater.(3)With the help of infrared thermal imager,the limestone loading test of limestone under different osmotic water pressures was carried out,and the acoustic emission ringing count and average infrared radiation temperature(AIRT)during the uniaxial loading process of limestone under different osmotic water pressures were compared and analyzed.AIRT-strain curve and stress-strain curve of sample have similar evolution trend,AIRT presented a rising trend with the increase of stress.Meanwhile,the irradiated thermal image can describe the process of rock sample failure under loading well.The infrared thermal image undergoes the low-temperature,temperature-rise period,high-temperature abnormal points and high-temperature abnormal surface until the specimen failure with the increase of the load,the abnormal phenomenon is obvious before the specimen structure instability,which can be used as the precursory criterion for the specimen instability.(4)The osmotic water erosion parameters are introduced into the Weibull distribution statistical constitutive model of rock damage,based on the mechanical properties of rock during uniaxial compression under the action of osmotic water pressure,the relationship between osmotic water and rock strength parameters is discussed,and the limestone softening constitutive model under uniaxial compression,which is applicable to the action of different osmotic water pressure is established.Based on the fracture mechanics theory and the stress state of micro-cracks in the rock,the prediction equation of the uniaxial compression damage threshold about limestone under different osmotic water pressure was established.The equation can well predict the stress and deformation of rock under different osmotic water pressure conditions,and the comparison of the experimental results and predicted results proves the rationality of the model.