Study On Deterioration Process Of Macro-mechanical Properties Of Limestone By Chemical Dissolution

In the southwest of China,limestone has the advantages of wide distribution,easy access to materials and good mechanical properties,and is one of the main foundation rock bodies for many projects such as slopes,dams and underground tunnels.However,due to the complexity of rock formation and environment,the interior of tuff often has numerous fissures,holes and other defective areas,which provides good conditions for the intrusion of natural water solutions into the rock interior.The long-term erosion of water solution will occur with the rock-forming minerals by dissolution and change the internal structure of the rock,which leads to the gradual deterioration of the macro-mechanical properties of the rock,which is a serious threat to the longterm stability and durability of the rock project.In view of this,dynamic dissolution experiments were carried out in deionized water solution,carbon dioxide-water solution and hydrochloric acid solution for limestone as the research object in this paper.The macroscopic mechanical properties,surface dissolution patterns and damage patterns of tuffs were investigated from the perspectives of different aqueous solution environments and the degree of mass loss of tuffs with dissolution time.The main work and research results of this paper are as follows:(1)In order to more realistically simulate the dynamic dissolution phenomenon between groundwater and rock in natural environment,a set of rock dynamic dissolution reaction device which can control the flow rate of water and constant partial pressure of carbon dioxide has been developed and designed independently.It mainly consists of carbon dioxide-water solution constant pressure reaction system,water solution flow rate control system,water-rock dynamic dissolution reaction system.The device provides an experimental basis for the study of the degradation process of macroscopic mechanical properties of tuffs by chemical dissolution in this paper.(2)Chemical dissolution experiments of tuffs in deionized water solution,carbon dioxide-water solution and hydrochloric acid solution environments were carried out,and uniaxial compression experiments were conducted on tuff specimens at each stage to obtain the uniaxial compressive strength,elastic modulus and damage patterns of rock samples at each dissolution stage under different aqueous solution environments.It was found that the trends of uniaxial compressive strength and elastic modulus of tuffs were basically the same,and both showed a decreasing trend with the increase of dissolution time.However,the degree of deterioration of macroscopic mechanical properties of tuffs by different aqueous solution environments was inconsistent,showing a pattern of: deionized aqueous solution < carbon dioxide-aqueous solution< hydrochloric acid solution.In addition,it was observed that the damage patterns of the tuffs were all dominated by brittle damage,accompanied by a large bursting sound.(3)By examining the calcium ion concentrations in aqueous solutions at different stages of dissolution,it was found that the changes of calcium ion concentrations in different aqueous solution environments showed a roughly increasing trend,which is consistent with the conclusion of the analysis of the chemical action mechanism of tuffs.The calcium ion concentration in solution reflects the reaction degree between calcite in tuff and chemical ions in different aqueous solutions,and the analysis of the three aqueous solutions shows that the calcium ion concentration presents a pattern of: deionized aqueous solution < carbon dioxide-aqueous solution <hydrochloric acid solution.With the increase of dissolution time,the surface color of chert specimens changed from milky white to dark and the surface of chert specimens became smooth from the appearance of numerous dissolution pores.(4)By tracking and monitoring the mass loss of tuffs at each stage,it was found that the overall mass loss rate of tuffs in different solution environments differed significantly and corresponded to the differences in the degree of chemical dissolution of tuffs.The degree of tuff mass loss showed a pattern of: deionized water solution < carbon dioxide-water solution <hydrochloric acid solution.Combining the changes of tuff mass loss with the changes of its macromechanical properties,the analysis found that: when the overall mass loss rate of tuff is within2.4%,the degree of attenuation of its macro-mechanical properties is larger as the overall mass loss rate of tuff increases,and when the overall mass loss rate of tuff exceeds within 2.4%,the degree of attenuation of macro-mechanical properties of tuff gradually decreases.