Study On Physical And Mechanical Properties And Damage Model Of Sandstone Under Acid Dry Wet Cycle

Sandstone and mudstone are the main types of cementation in coal measures in China.The main cementation methods are pore type calcium cementation and argillaceous cementation.Under the action of water,the softening phenomenon is obvious.In addition,in the process of dissolving minerals,groundwater often presents acidity or alkalinity,including Cl-,SO42-ions,which makes the physical and mechanical properties of surrounding rock decline,resulting in roof falling,surrounding rock expansion,floor heave and deformation,which seriously threatens the safety of the roadwayTaking the surrounding rock(sandstone)of coal mine underground roadway as the research object,after the dry-wet cycle treatment in different concentration of sulfuric acid solution,the change rules of physical indexes such as mass,P-wave velocity,porosity and pH value of solution under different pH value and dry-wet cycle times were studied respectively.Meanwhile,through uniaxial compression test,Brazilian split test and one-dimensional SHPB impact test,the mechanical properties of sandstone under acid dry-wet cycle were summarized and analyzed.Combined with the micro structure change and the diffraction pattern analysis of sandstone before and after the reaction,the damage evolution mechanism of sandstone under the acid dry-wet cycle was described.Finally,according to the test results,the damage variable was established based on Weibull statistical distribution,and the damage constitutive equation of sandstone under uniaxial compression was deduced and verified.The test results show that:Under the action of acid dry-wet cycle,the physical and mechanical indexes of sandstone show obvious deterioration.The pH value of soaking solution,the quality and P-wave velocity of sandstone,and the uniaxial mechanical indexes all show that 10 times of dry-wet cycle is the turning point of deterioration,and then the change rate of each index will increase sharply.Micro analysis and XRD diffraction images before and after the test also confirmed that the formation of gypsum,calcium silicate and other cements in the early stage of the dry-wet cycle would delay the damage of the dry-wet cycle,until the later stage of the crack development,the phenomenon disappeared.However,the decrease of tensile strength and dynamic compressive strength is not affected by the formation of cement,and the corresponding tensile strength and fractal dimension index show a trend of gradual deterioration with the increase of acid dry wet cycles.Finally,based on the Weibull distribution of statistical probability distribution,the uniaxial damage constitutive model of sandstone under different acid concentration was derived,and the calculated value of the model is basically consistent with the test value.Figure 54 table 22 reference 81...