Study On Physical And Mechanical Properties Of Limestone Under Alternate Action Of Acid Rain And High Temperature

From June to September every year,the surface strata in Chongqing are frequently exposed to high temperature and acid rain.According to the relevant geological survey,limestone is one of the most common surface rocks in Chongqing area,and its minerals contain a lot of CO32ions.In acid environment,CO32-containing minerals in limestone will react with H+ions in acid rain solution,which will change the content of minerals and reduce the internal structure of cementitious materials,and then lead to obvious changes in macro mechanical properties,and even lead to the overall instability of rock mass.In order to ensure the safety and stability of the construction project,this paper studies the physical and mechanical changes of limestone and its deterioration effect in the typical acid rain high temperature environment of Chongqing area,taking the number of alternate action as the variable.In terms of mechanical properties,the variation law of limestone test parameters with the number of alternating actions is studied through laboratory tests;in terms of deterioration effect,the macroscopic deterioration effect of mechanical properties is studied based on the variation law of mechanical properties;in terms of microscopic deterioration effect,the microscopic deterioration effect of limestone minerals with the number of alternating actions is studied from the variation of microscopic mineral content.Finally,based on the degradation law of each test parameter,the constitutive model of limestone is established by fully considering the relationship between the number of alternate actions,confining pressure,internal friction angle and stress.The main research contents and achievements of this paper are as follows.(1)In order to study the effect of acid rain high temperature alternation on the physical and mechanical properties of limestone,acid solution with a certain pH value was prepared.After soaking limestone for a certain time,the limestone was subjected to high temperature action at a set temperature,and then cooled naturally.Five kinds of alternating action times(0,5,10,15,20)were designed.The physical and mechanical properties of limestone under different times of action were tested,and the mass loss rate,uniaxial compressive strength,uniaxial compressive elastic modulus and deformation modulus,triaxial compressive strength,triaxial compressive elastic modulus and deformation modulus and Brazilian splitting strength parameters of limestone were obtained.The mechanical changes of limestone under different times of acid solution high temperature alternating action were discussed.The results show that,within the range of alternate action times,the test mechanical parameters show a trend of weakening with the increase of action times;in addition to the logarithmic correlation between mass loss rate and action times,there is a good quadratic polynomial correlation between other test mechanical parameters and action times,and they all show a trend of decreasing with the increase of action times As a result,the brittleness is continuously weakened and the plasticity is enhanced.(2)Used total degradation stage Dj,degradation degrees ?Dj and phase within the average degradation degree ?Djn calibration different acidic solution-high temperature under the action of alternating limestone degradation degree of the test parameters.Calculated based on test results,the physical and mechanical parameters of Dj,?Dj and ?Djnvalue,will be the total degradation degree average fitting parameters,then normalized processing,finally,the normalized function derivation,the degradation rate of the test parameters.The degradation rate of different parameters is characterized by the degradation coefficient CD,and the degradation order of physical and mechanical parameters of limestone under different acid solution high temperature alternating action times is mica(micro)>uniaxial compressive strength>triaxial deformation modulus>calcite(micro)>uniaxial elastic modulus>triaxial elastic modulus>triaxial compressive strength>dolomite(micro)>internal friction friction angle>indirect tensile strength>uniaxial deformation modulus>cohesion.According to the sequence of degradation strength,four stages of degradation effect of limestone under different acid solution high temperature alternation times are obtained,which are:? microscopic Mineral chemical reaction stage;?beginning stage of mechanical damage;?extension stage of mechanical damage;? stable stage of mechanical damage.(3)According to the degradation rate results of various mechanical parameters of limestone under different acid solution high temperature alternation times,and fully considering the elastic modulus,confining pressure,alternation times and internal friction angle,based on the continuous damage factor,Weibull distribution statistical theory and strain equivalence assumption proposed by Lemaitre,the uniaxial and uniaxial stress models of limestone under acid rain high temperature deterioration are established damage constitutive model of triaxial compression.The established statistical constitutive model is verified by the experimental data,which shows that the model can basically reflect the stress-strain curve characteristics under uniaxial and triaxial compression conditions,but the theoretical value is larger than the experimental value.In addition,in the range of acid rain solution high temperature alternating action times,the damage degree of various strength of limestone from large to small order is:uniaxial compressive strength damage>triaxial compressive strength damage>indirect tensile strength damage,that is,the damage degree of uniaxial compressive strength of limestone is the most serious.