Study On The Damage Mechanical Properties Of The Sandstone Under The Acid Chemical Erosion Conditions

Deep rock engineering is often affected by groundwater erosion,the long-term erosion would create cracks and pores in the wall rock and increase the porosity and permeability so that makes a negative impact on the stability of the wall rock in deep engineering.As the natural meteoric water penetrates into the deep subsurface,which covers a number of ions like Na⁺,K⁺,H⁺,CO₃^2-,Cl^-,etc.,the weak acidity of groundwater will intensify.On the other hand,the environmental pollution in recent years,such as acid rain,sewage discharge,etc.,has made a serious impact on the groundwater environment,and enhanced the erosion of groundwater.This paper systematically studies the effect of acid chemical erosion duration on the physical properties of sandstone,in the way of taking red sandstone as the research object and deploying ion concentration to simulate the acidic environment in deep groundwater.With the help of acoustic emission test device and scanning electron microscope(SEM)device,the degradation mechanism of the mechanical properties of sandstone after acid chemical erosion was investigated.Based on the split Hopkinson pressure bar(SHPB)system and 3D digital image correlation(3D-DIC)technique,the mechanical properties and damage characteristics of sandstone were analyzed,which was under the coupling condition of acid chemical erosion and impact load.The main contents and research results of this paper are as follows:(1)Preparing an acidic chemical solution with a p H of 3 to simulate the deep groundwater environment,and measuring the various physical properties of red sandstone in different soaking duration.The results showed that,within 28 days'immersion,the longitudinal wave velocity and the drying quality of the sandstone sample showed a negative correlation tendency with the soaking duration overall,and the longitudinal wave velocity were more sensitive to soaking duration.(2)Uniaxial compression tests were carried out on red sandstone samples with different soaking duration.It can be found that with the increase of soaking time,the stress-strain curve of sandstone increased gradually in the compaction stage and fluctuates obviously in the yield stage.As the erosion going on,the uniaxial compressive strength and elastic modulus would decrease,while the peak strain increased.Acoustic emission tests and SEM results showed that the cement and mineral composition in sandstone would have an outside-in reaction with H+in acidic solution,and the cementation ability between mineral particles would decrease,with the increase of micropores.(3)The impact tests were performed on red sandstone samples with different soaking times,and it can be found that with the significant increase of strain rate,the sensitivity of dynamic compressive strength and dynamic elastic modulus of sandstone to soaking time is gradually enhanced.Both of them are positively correlated with strain rate and negatively correlated with soaking time.Besides,3D-DIC results show that acidic chemical erosion changes the sandstone damage mode from the tensile to the shear damage,and the micro-pores inside the sandstone caused by acidic chemical erosion make the stress concentration more likely to appear.(4)A damage constitutive model of the sandstone coupled with the chemical erosion and loading was developed,and a softening factor K was also introduced to characterize the effect of acidic chemical erosion on the rock strength under the medium to high strain rate.It was found that the proposed model could better describe the mechanical behavior of the sandstone under the static and dynamic loading after the chemical erosion comparing with the measured stress-strain results.(5)Exploring the energy dissipation law of the sandstone in the impact tests,the results show that:the reflected energy gradually increases,and the transmitted energy almost remains stable,while the dissipated energy gradually decreases with the increase of the soaking time under the same incident energy.Further,the sensitivity of the dissipative energy reduction to the soaking time gradually increases as the strain rate increases.This work has 55 figures,11 tables,and 95 references.