Macroscopic And Mesoscopic Analysis Of Physical And Mechanical Properties Of Acid Corroded Sandstone

With the rapid development of China's economy,a large number of rock engineering emerged,accompanied by more and more environmental geotechnical engineering problems,including rock damage in acidic environment.Physicochemical reactions between acid solutions and rocks lead to changes in rock micro-characteristics,while macro-mechanical properties deteriorate,which brings hidden dangers to the long-term stability and safety of rock engineering.In this paper,the macro-and meso-properties of sandstone in acidic environment are studied by means of CT scanning test and SEM test of Acid-Corroded sandstone.The CT scanning images and scanning electron microscopic images of sandstone in different immersion stages were obtained.The qualitative and quantitative analysis of the images was carried out,and the meso-structure of sandstone damage was analyzed from different scales and regions.Through uniaxial compression test,solution ion concentration test and secondary porosity test of Acid-Corroded sandstone,the variation law of physical and mechanical parameters of sandstone is analyzed,and the evolution law of Acid-Corroded damage of sandstone is discussed.The following research results are obtained:1.Through the CT scanning experiments of sandstone in different soaking stages,the gray level changes of CT images were qualitatively analyzed.The corrosion depth of sandstone was obtained by binarization of CT images,and the formula of corrosion depth and immersion time was established.Quantitative study was carried out based on the number of CT images,and the changes of mean and variance of CT images in the whole region and the selected area were analyzed.The CT number distribution histograms of upper,middle and lower sections of natural samples were studied,and the changes of peak frequency and corresponding CT values were analyzed based on the CT number distribution histograms of sandstone in different corrosion stages.2.Scanning electron microscopy(SEM)experiments of sandstone in different soaking stages were carried out to qualitatively analyze the scanning electron microscopy(SEM)images of the corrosion zone.The relative content of elements in sandstone before and after immersion was obtained by electron spectroscopy.The pore parameters were analyzed based on binary electron microscopy images.The correlation between average pore parameters in different soaking stages was studied.With the prolongation of corrosion time,the pore area increases,the mineral particle structure becomes loose gradually,and the pore is connected to form large pore.The plane porosity,average diameter,average roundness and fractal dimension of the pore increase gradually,while the number of the pore increases first and then decreases.3.The mechanical parameters of sandstone in each immersion stage are obtained by uniaxial compression test.With the extension of corrosion time,the uniaxial compressive strength and elastic modulus of sandstone decrease gradually.The damage models of specimens at different meso-scales are established.The relationship between cationic dissolution rate and secondary porosity of sandstone with soaking time was analyzed.The relationship among damage variables based on secondary porosity,pore distribution and strength is also discussed.