A Study On The Damage Characteristics Of Limestone Under The Action Of Acidic Dry-wet Cycles

As a widely existing engineering material in nature,rock is not only complex in structure,but also has certain pores,fracture surfaces and joints inside.These defects will cause the mechanical properties of the rock to change greatly with the change of the external environment,and the stability of water to geotechnical engineering cannot be ignored.In view of the above problems,this paper selects a slope limestone in Chongqing as the research object,and soaks in dilute sulfuric acid solution with p H=3,p H=5,and p H=7respectively.The damage characteristics of limestone under different acidic dry-wet cycles were explored.The main research contents and results are as follows:(1)The physical parameter damage characteristics of limestone under the action of acidic dry-wet cycle are studied.In a limited space and a relatively closed environment,the change of physical properties of limestone is time-sensitive: in the initial stage of soaking,the acid solution diffusion is the main effect,and the reaction is mainly Concentrated on the surface of the sample,with the increase of the number of cycles,the concentration of Ca2+ and Mg2+ in the solution increased,and the chemical reaction rate of water gradually decreased,and finally became stable.And the relationship between mass loss and penetration damage depth is deduced.(2)Uniaxial compression test and triaxial test were carried out to study the damage characteristics of limestone strength parameters under the action of acid dry-wet cycles.The obtained limestone mechanical parameters have a logarithmic relationship with the number of acid-wetting cycles,that is,in a limited space and relatively closed environment,the corrosion damage of limestone by acid-wetting cycles will gradually tend to a stable state after a certain period of time.Normalize the fitted function.The degradation effects of the mechanical strength parameters of limestone are obtained in descending order: shear strength,uniaxial compressive strength,cohesion,and internal friction angle.(3)The changes of Ca2+ and Mg2+ in the acid soaking solution were measured by EDTA,and the law of incremental change of limestone porosity was obtained.The damage mechanism of limestone is analyzed from the perspective of porosity evolution,and the calculated porosity is compared with the measured porosity,and it is found that the measured porosity is slightly larger than the calculated porosity.Dissolution of limestone mineral particles.In fact,some mineral particles will peel off under the action of drying and wetting cycles,and form flocculent precipitation in the soaking solution,resulting in a small increment of calculated porosity.The study shows that the increase of limestone porosity is linearly related to uniaxial compressive strength,internal friction angle and cohesion damage.(4)Taking the elastic modulus as the damage variable of acid dry-wetting cycle,and assuming that the damage of micro-elements obeys the Weibull distribution under the load,the damage variable under load is established based on the D-P criterion.The damage and deterioration law of limestone under the action of acid-dry-wet cycle-load coupling was explored,and the damage statistical constitutive model of limestone under the action of acid-dry-wet cycle was established by using the continuous damage theory and the Lemaitre strain equivalent assumption.It is found that the uniaxial compression test values are distributed along the curve calculated by the model,which shows that the model can well reflect the stress-strain curve characteristics of limestone under the action of acid-dry-wet cycles.