Experimental Study On Dynamic Mechanical Properties Of Limestone After Chemical Corrosion

The phenomenon of chemical corrosion of groundwater exists widely in lithosphere,but the surrounding rock of underground engineering is often deformed and destroyed due to dynamic load,in addition to the influence of groundwater wetting effect.Therefore,it is of great significance for efficient and safe underground production to study the damage evolution and fracture mechanism of rock mass mechanical properties under impact loading.Taking limestone as the research object,by configuring chemical solutions with different pH values,setting up multiple levels of corrosion time,obtaining corresponding corrosion damage samples,looking into mechanism of chemical corrosion damage with the help of X ray fluorescence analysis and nuclear magnetic resonance?NMR?technology,then based on the Hopkinson pressure bar system,a series of dynamic impact tests were carried out on corroded limestone samples,at the same time,the failure process of the sample was tracked by high speed camera.The following research results are obtained:?1?The acidity-alkalinity of the solution in rock chemistry has the character of self-equilibrium.Acid-base solution tends to be neutral gradually with the extension of corrosion time,while neutral solution tends to be weakly alkaline gradually.After chemical corrosion,the quality of limestone samples will decrease to varying degrees,and the porosity will increase accordingly,and the lower the solution pH value,the longer the corrosion time,the more serious the damage degree of the sample.?2?Acid solution was the most obvious corrosion damage of limestone,followed by alkalinity,and neutral environmental lithology is the most stable.With the increase of corrosion time,the impact damage degree becomes more and more serious,and the fractal dimension also increases.The dynamic compressive strength,peak strain and elastic modulus deteriorate with the increase of corrosion damage.It is also found that the dynamic compressive strength and elastic modulus of samples increase linearly with the increase of strain rate,which shows obvious strain rate strengthening effect,but in terms of strain rate sensitivity,the natural state sample is stronger than the corrosion sample.?3?With the continuous development of chemical corrosion,the dynamic tensile strength,dissipated energy and specific energy absorption of the samples all show a three-stage change law.At the same time,the splitting failure of high speed camera recording test first produces a small crack in the center line of the disk,then,the main fracture surface is developed along both ends of the radial direction,and its fracture location is mainly concentrated on the propagation path of the incident wave,that is,it presents a horizontal crack along the diameter of the sample.?4?The fracture of the sample starts from the tip of the prefabricated crack and extends along the direction of loading.After the failure,the samples continue to rotate at a uniform speed around the contact point O between the sample and the incident bar.The pH value of chemical solution has a great influence on the fractal dimension of crack propagation,When pH=6,the fractal dimension of crack growth did not change significantly with corrosion time,while the fractal dimension of crack growth in corrosion samples with pH values of 2 and 4showed an increasing trend in corrosion time dimension.With corrosion time prolonging,the dynamic fracture toughness values K_?shows a three-stage drop characteristic,and the W/Wi ratio and fracture energy WF of the sample also show a three-stage drop characteristic,which decrease rapidly with the increase of corrosion time,then gradually slow,and finally tend to be stable.?5?After chemical corrosion,the combined contents of CaO,CO₃,MgO,and Fe₂O₃ in the mineral composition of limestone decrease with the increase of corrosion time,while SiO₂,Al₂O₃ and other substances show an increase law,and the longer the corrosion time,the lower the pH value of the solution,and the more obvious the change of mineral content.