Study On Degradation Law And Damage Mechanism Of Pull-down Mechanical Properties Of Limestone TMC Coupling

Because rock materials are natural materials formed under certain conditions in nature,they are considered to be a heterogeneous and discontinuous material,and most rocks contain more natural fractures.In rock engineering,fractured rock often undergoes various forms of fracture failure,and tensile fracture is a common type of failure in rock engineering.Rock fracture damage will also be affected by the natural environment and geological conditions.The limestone mountain in Guilin area is affected by high temperature,acid rain and human activities for a long time,and the dangerous rock collapses.In this paper,the macro-mechanical test of tensile-shear mechanics under the interaction of indoor thermo-mechanical-chemical interaction is carried out in limestone of Guilin area.The effects of temperature action and chemical solution erosion on the mechanical properties of rock are analyzed,and the rock damage mechanism effected by various factors is discussed.The main research and achievements are as follows:1.The tensile cracking test of single-fracture limestone after immersion in acidic solution with different pH and different pH values was carried out.The crack propagation law and failure mode of single-fracture limestone shear-shear failure were analyzed,and the deterioration law of tensile-shear mechanical properties was obtained..The results show that the crack propagation law of single fractured rock after immersion in different temperature and different pH values is basically the same.The shear failure of a single-fractured limestone can be roughly divided into three stages:the first stage is the shearing to the cracking,the second stage is the unloading,and the third stage is the extension to the through.Chemical corrosion can change the internal microstructure of the rock,making the rock loose and fragile,and more prone to deformation.At the same time,the exothermic effect of the water-rock reaction also has a certain impact on the structural damage of the rock.Macroscopically,it is mainly manifested in the deterioration of mechanical properties.The temperature can cause volume expansion and thermal stress of the crystal minerals inside the rock.At the same time,the temperature increase will accelerate the rate of chemical reaction and aggravate the damage and deformation of the rock structure.The macroscopic performance is mainly manifested in the deterioration of mechanical properties.2.X-ray diffraction,electron microscopy and electron spectroscopy were used to analyze the mineral composition and surface micromorphology of the rock samples before and after soaking.The results show that the mineral composition of limestone is mainly calcite,which is in the rock sample soaked in acidic solution.Gypsum was detected,which is primarily a product of the reaction of calcite with sulfuric acid in solution.In the natural state,the microstructure of limestone is basically composed of closely arranged rhombohedral crystal particles.The particles of these rhombohedrons are mainly calcite,which constitutes the overall framework of the internal structure of limestone.After the corrosion,the crystal grain arrangement of the limestone rhombohedron becomes loose,the calcite crystals are dissolved,the particles become relatively round,the edges and corners are smoothed to varying degrees,and large pores appear between the crystal grains and secondary cracks appear.3.The aqueous solution was analyzed using an inductively coupled plasma emission spectrometer and a pH test pen.The results showed that the pH value of the acid solution and distilled water after immersion for 30 days increased to different degrees.The concentration of Ca²⁺in the solution after soaking is much higher than the concentration of other ions.The concentration of various ions in the solution is roughly inversely proportional to the pH value and proportional to the temperature.The rock mass loss rate visually reflects the degree of rock damage:the smaller the pH value of the solution,the more serious the damage to the rock and the higher the mass loss rate;the higher the solution temperature,the more serious the damage to the rock and the higher the mass loss rate.4.By studying the damage of rock structure from different microscopic angles,it is fully proved that both PH value and temperature affect the progress of water and rock to a certain extent,which has an impact on the deterioration of rock mechanical properties.