| In the process of underground engineering,deep rock mass engineering,dams,tunnel excavation and mine excavation,due to the action of groundwater,some rock masses are in a long-term environment of alternating drying and wetting cycles.The long-term physical and chemical interaction between water and rock makes The number of holes and fissures in the rock gradually increased,leading to instability and destruction of rock mass engineering.During the construction process,the engineering rock mass structure is not only subject to static mechanics,but sometimes also to dynamic mechanics caused by blasting,mechanical excavation,rock bursts and earthquakes.Rocks are not only subject to some physical effects in the underground environment,but also chemical effects in the underground environment.Because the discharge of industrial water and domestic water and heavy metal pollutants flow into the deep underground along the soil,the water in the underground environment is acidic.Therefore,the groundwater will contain more SO42-,Cl-,HCO3-,CO32-and other ions that can make the groundwater acidic,while the Ca2+ And SiO2 and other minerals will react with various ions in the aqueous solution and reduce the strength of sandstone.Long-term exposure to an acidic underground aqueous solution will dissolve minerals in the rock and increase internal pores and fissures.Therefore,it will have a certain impact on the basic mechanical properties of the rock and cause it to change.In view of the problems encountered in the above projects,this article takes the deep sandstone under the acidic drying and wetting cycle environment as the research object,and then analyzes the results through theoretical analysis and experimental research,using XRD ray diffractometer and scanning electron microscope(SEM)And other equipment,sorted out and analyzed the mechanical properties and damage mechanism of deep sandstone under the action of acidic drying and wetting cycles,and reached the following conclusions:(1)With the increase of the drying and wetting cycle period and the decrease of the pH value of the solution,the strength value of the sandstone is gradually reduced,and the total degradation degree is gradually increased.The degradation degree of the sandstone test block is 28.77%when the pH value is 3 in 30 wetting and drying cycles.It shows that when the acidity of the sandstone test block is constant,the deterioration degree of the sandstone increases with the increase of the drying-wetting period.The average stage degradation degree of sandstone under different drying and wetting cycles of pH 3 is 11.53%,3.42%,2.60%,1.24%and 0.97%,respectively.The average stage degradation degree is the largest during one drying and wetting cycle.It is concluded that the average degradation degree of sandstone gradually weakens with the increase of the number of wetting and drying cycles.The strength degradation of sandstone in pH 3,5,distilled water and 7 solutions during a drying and wetting cycle is 11.53%,5.35%,2.03%and 1.83%,respectively.This shows the strength degradation of sandstone.The degree gradually increases as the acidic pH of the solution decreases.The peak strain and ultimate stress of sandstone gradually decrease with the increase of the drying and wetting cycle period,and gradually move to the right as the acidity of the solution increases.(2)The dynamic uniaxial compressive strength test of sandstone under different impact pressures(0.55MPa,0.70MPa,0.85MPa,)was carried out on the acidic drying-wetting cycle period.In the stress-strain curve of sandstone,the compaction stage and the plastic deformation stage gradually increase,the length of the elastic stage gradually decreases,and the dynamic uniaxial compressive strength value gradually decreases.When the impact pressure is 0.55MPa,the dynamic uniaxial compressive strength values of sandstone in the solution with pH values of 3,5,distilled water and 7 respectively in a dry and wet cycle are reduced by 15.12%,9.72%,7.12%and 3.1%.compared with those in the dry state.When the impact pressure is 0.55MPa and the pH value is 3,the strength value of sandstone at 1,5,10,20,and 30 dry and wet cycles is reduced by 15.12%,23.00%,26.37%,35.45%,and 39.85%.respectively,compared with the drying state.(3)Through screening test and analysis of dynamic uniaxial compressive strength test block under acid drying and wetting cycle,the fractal dimension of sandstone is gradually increased with the increase of drying and wetting cycle period and the decrease of solution pH value.When the impact pressure is 0.85 MPa,the fractal dimension of sandstone is 2.00,1.98,1.95 and 1.93 in the solution of 3,5,distilled water and 7 respectively,and the fractal dimension of sandstone is the largest when the solution pH is 3.When the impact pressure is 0.85 MPa,the fractal dimensions of sandstone after crushing are 2.00,2.04,2.07,2.09 and 2.12 respectively when the impact pressure is 0.85 MPa,and the fractal dimension is the largest when the drying and wetting cycle period is 30.(4)Through XRD test and SEM test,the sandstone undergoing acidic drying and weting cycle period was observed and analyzed the changes in chemical composition and microstructure of sandstone particles.As the pH value of the solution decreased and the drying and wetting cycle period increased,the internal sandstone The number and size of holes and fissures are gradually increasing.The minerals contained in the sandstone,such as calcium carbonate,quartz,albite,and potassium feldspar,dissolve with H+in the solution,which increases the number of pores and cracks in the sandstone and reduces the strength of the sandstone.The drying and wetting cycle makes the sandstone internal The dissolution of the soluble substance causes the damage to increase.Figure 40 reference 74... |
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