Corrosion Damage And Analysis Of Macro-Micromechanical Characteristics Of Sandstone Under Acidic Environment

The research on rock damage in acidic environment is a very important subject in environmental geotechnical engineering.After the rock is corroded by acid,the interaction between the particles in the rock and the lattice of the mineral particles is weakened by the corrosion of the acid,and the physical and mechanical properties of the rock are greatly changed,which threatens the long-term stability of the rock engineering.In this paper,the common sandstone is selected as the test material,and the accelerated corrosion test is simulated by sulfuric acid solution with pH = 1 and pH = 3.The effects of pH value,ionic concentration,sandstone quality and water content on the sulfuric acid solution in different corrosion stages were monitored.Combined with the uniaxial compression test and CT scanning test of corroded rock samples,the physical,chemical and mechanical properties of the sandstone are analyzed during the process of acid corrosion.The changes of physical and chemical properties and damage evolution laws of sandstone during the process of acid corrosion are revealed,and the relationship between the CT number and the mass and density of corrosion samples is analyzed from the microscopic point of view.The main research results are summarized as follows:?1?The changes of the mass change,the change of water content and the change of pH value of the sandstone samples in different concentrations of sulfuric acid solution show obvious characteristics.The pH value of the sulfuric acid solution after soaking showed a trend of increasing,and with the increase of the immersion time,the pH value of the solution gradually stabilized.The rate of change in quality is increasing throughout the corrosion phase,but the growth rate decreases after 90 days.The water content increased first and then decreased.?2?The cationic concentration of Na⁺,K⁺,Mg²⁺,Ca²⁺ in different concentrations of sulfuric acid solution showed that the cation dissolution rate reached the maximum at the initial stage,and the dissolution rate of Ca²⁺ was the fastest.The maximum dissolution rate of Ca²⁺ in pH = 1 sulfuric acid solution is 8.07 mg/d,which is 3 times of Ca²⁺ dissolution rate in pH = 3 sulfuric acid solution.Compared with the dissolution rate of Na⁺ and Ca²⁺,the dissolution rate of K⁺ and Mg²⁺ is much smaller,changes are more stable in the test process.In the same immersion stage,the stronger the acidity,the greater the dissolution rate of the cation in the solution.?3?The stress-strain curves of sandstone samples in different corrosion stages are obtained by uniaxial compression test.It is found that the uniaxial compressive strength of sandstone decreases with the prolongation of immersion time,and the process of rock samples from elastic-plastic stage to failure stage is prolonged.At the same time,through the analysis of the corrosion stage,the relationship between the penetration depth and the uniaxial compressive strength of different rock samples is established.?4?Sandstone in the process of acid corrosion,the results of CT scanning show that the CT number of the rock sample increases due to the diffusion of the acidic solution,and the CT number of the rock sample decreases with the immersion time.At the same time,the relationship between CT number and density of acid corrosion samples was deduced,and the change of density and mass change of sandstone samples in different corrosion stages is obtained.The damage variables of different corrosion stages are calculated.It is found that the damage variable of rock samples increases with the increase of corrosion time.