Strength And Creep Properties Of Sandstone In Acid Environment And Dry-Wet Cycle

China has a vast territory and many waters,and the interaction of water and rock can be said to occur all the time.In the process of geotechnical engineering construction and underground space development,people often encounter engineering safety problems caused by various water-rock interactions.Therefore,it is of great significance for the safe construction of underground geotechnical engineering to carry out research on the influence of dry-wet cycle and chemical corrosion on rock mechanical properties.Combining the experimental research foundation of predecessors and the existing experimental conditions,the method of combining mechanical test(uniaxial and triaxial compression test,creep test),microstructure analysis and theory was carried out to carry out the dialogue between acid environment and dry-wet cycle.A study on the influence of the law on the mechanical properties of sandstone.The test samples were selected from the whole piece of white sandstone in the southwest of Sichuan Province,and the test pieces were made into standard cylindrical test pieces after processing and grinding.The acidic and neutral environments were designed to carry out 5,10,20,and 30 drywet cycle tests respectively.The specimens obtained after dry-wet cycles were subjected to uniaxial and triaxial compression tests and creep tests,carry out data statistics and calculation analysis on the test results,and analyze the mechanical properties(compressive strength,elastic modulus,cohesion and internal friction angle,etc.)of white sandstone after dry-wet cycles in acidic and neutral environments and the number of cycles.The regularity of the dry-wet cycle was explored.The changes in the mineral composition of the white sandstone before and after the dry-wet cycle were analyzed by X-ray diffraction analysis,and the damage to the rock caused by the dry-wet cycle was revealed from the microscopic level by scanning electron microscopy.Two aspects of wet cycle effect describe the deterioration principle of white sandstone with wet and dry cycle in acidic environment.A simulation experiment was carried out on the white sandstone subjected to dry-wetting cycles in an acidic environment by ABAQUS,and the comparison with the actual experiment was carried out.The main research results of this paper are as follows:(1)Through the preliminary investigation of rock samples from different regions,the white sandstone blocks in the southwest of Sichuan Province were finally selected as the test materials,and standard cylindrical specimens were processed and prepared.Different times of dry-wet cycle tests in acidic and neutral environments were designed.(2)Uniaxial and triaxial compression tests were carried out on the white sandstone specimens obtained by dry-wet cycles in acidic and neutral environments,and the stressstrain curves and elastic modulus of the white sandstone specimens under different solution environments and cycles were analyzed.The change law of mechanical properties such as weight,compressive strength,and internal friction angle and cohesion.It is found that the variation laws of compressive strength and elastic modulus of white sandstone in acid and neutral environments with dry and wet cycles are basically the same.trend of increasing first and then decreasing.The internal friction angle of white sandstone with dry-wet cycle in acidic environment and neutral environment is basically unchanged,with a small decrease,while the cohesion shows a significant decrease.The compressive strength,elastic modulus,internal friction angle and cohesion of the white sandstone in the dry-wet cycle in an acidic environment are significantly lower than those in the dry-wet cycle in a neutral environment.(3)SEM scanning test and X-ray diffraction analysis test were used to observe the white sandstone with different cycles in acidic and neutral environments,and the influence of dry-wetting cycles on the white sandstone was analyzed.From a microscopic perspective,the damage of dry-wet cycles to rocks is mainly caused by the influence of the number of pores in the rock,the destruction of the integrity of the crystal structure of the rock,and the development of pores in the rock,which leads to a significant decrease in the mechanical properties of the rock.In terms of changes in rock mineral composition,chemical corrosion and dry-wet cycles have resulted in hydrolytic corrosion of illite and kaolin,resulting in a continuous decline in rock quality,which in turn leads to rock deterioration.(4)A uniaxial creep test was carried out on the white sandstone after dry-wet cycles in acidic and neutral environments,and the experimental data were drawn using the Boltzmann superposition theory.Through the analysis and calculation of the obtained experimental data,we obtained the creep characteristics data of white sandstone under different load levels after different cycle times in acidic environment and neutral environment were obtained,and the law of dry-wetting cycle times and long-term strength was obtained by isochronous stress-strain curve method.It is found that both the acid environment and the dry-wet cycle have a greater impact on the creep deformation of the white sandstone,and the effect of the acid environment on the strength of the white sandstone is smaller than that of the dry-wet cycle on the long-term strength of the white sandstone.With the continuous progress of the cycle experiment,the long-term strength is continuously reduced,and the mechanical properties are continuously deteriorated.Under the same number of cycles,the instantaneous creep rate and steady-state creep rate are larger in the acidic environment.(5)Using the numerical simulation software ABAQUS,the compression simulation test was carried out on the white sandstone that has experienced different times of drying and wetting cycles in an acidic environment.The simulation results are compared with the data obtained from the actual test,and the experimental values are basically consistent with the simulated values.