Study On The Mechanism Of Water-rock Interaction Degradation Of Rock Physical And Mechanical Properties

Under natural conditions,the physical and chemical interactions between rock mass and groundwater continue to occur,resulting in damage to rock mass structure and deterioration of mechanical properties,which seriously threatens the safety of geotechnical engineering such as slopes,dam foundations,and underground structures.Studying the mechanism of water-rock damage to rock structure has positive significance for preventing and controlling geological disasters.This article explored the effect of long-term immersion on limestone and wet-dry cycling on the mechanical properties and microstructure of sandstone,and examined the changes in strength,elastic modulus,and porosity of rock samples before and after in water-rock interaction.The main research work and results obtained are as follows:1.Distilled water and p H = 2 solution were used to immerse the limestone samples for 80 days under a sealed condition,and the mass ratio of water-rock was 2:1.Uniaxial and triaxial tests were carried out on the limestone samples before and after immersion,and the microscopic morphology of the natural and soaked samples was observed using a scanning electron microscope.In addition,the microscopic pore characteristics of the samples were analyzed in combination with image processing technology,and the mechanism of deterioration of the mechanical properties of limestone was discussed based on the existing research results and the characteristics of the rock itself.The test results showed that the strength and elastic modulus of limestone after erosion by the aqueous solution are reduced;the failure mode of the limestone after soaking under uniaxial test conditions is shear-tensile composite failure,while the natural limestone is shear failure.The failure modes of limestone specimens under triaxial test conditions are all shear failures.The number of microscopic pores of the sample after immersion increased.In the same area,the pore area of the sample after p H=2 solution immersion was the largest,followed by distilled water immersion,and the natural sample was the least.The result of water-rock interaction is influenced by water solubility,water-rock interaction and rock lithology.The dissolution reaction not only occurs on the surface of limestone,but also enters the interior of the rock through natural cracks,which corrodes the crack surface and leads to the macroscopic mechanical damage of the rock.2.Sandstone samples were subjected to 0,1,5,10,and 20 wet and dry cycle tests.After each cycle,the P-wave velocity of the samples were tested,and the ions in the soaking solution were tested.After the wet-dry cycle test is completed,the uniaxial test were carried out on the samples,and the changes in the microstructure of the sample are studied using scanning electron microscope(SEM),nuclear magnetic resonance(NMR),and 3D measurement microscope.The test results showed that the rock P-wave velocity decreases with the increase of the number of dry-wet cycles,but the rate of decrease gradually slows down,and the wet-dry cycle causes the strength and elastic modulus of the sandstone to decrease.The microscopic pores number and the total pores area increases of the rock with the number of wet-dry cycles times,but the growth rate gradually decreases.The surface roughness of sandstone decreases with the number of wet-dry cycles times.During the wetting process,the sandstone cement material was dissolved out,and the mineral connections became loose.During the drying process,different minerals had different expansion capacities,the minerals were squeezed against each other,the secondary cracks increased,and the sandstone structure damage was further aggravated.