Study On Anisotropic Mechanical Properties Of Layered Limestone Under Acidic Dissolutio

Most of the overlying rocks of coal mines in Guizhou are carbonate rocks with a laminated structure,whose layers,weak interlayers or mining-induced rock damage and fractures result in significant heterogeneity and anisotropy in the physical and mechanical properties of the rock,providing a material basis and space for movement for hydration dissolution and solute transport,while rock dissolution and disintegration promote the expansion of existing fractures,causing increased seepage and ultimately leading to rock engineering instability.The closure of the mines has resulted in a rise in the water table which is acidic or weakly acidic,enhancing the corrosive effect on the rock and seriously affecting the mechanical properties of the rock.Therefore,it is particularly important to understand the characteristics of the deterioration of mechanical properties caused by acid dissolution on rock masses.To this end,based on previous studies,dissolution tests,mechanical tests and numerical simulations of laminated tuffs under different acid solutions were carried out to explore the deterioration mechanism and damage evolution process of physical and mechanical properties of laminated tuffs caused by acid dissolution,and to conduct scientific analysis and research on the deformation and damage of rock masses under chemical dissolution.The main findings are as follows:（1）The solution p H（2,3,4 and 5）was used to analyse the macroscopic surface characteristics,microscopic morphological characteristics,mass loss,wave velocity,ion concentration,electron microscopy and nuclear magnetic resonance（NMR）of tuffs before and after dissolution in different acidic environments and at different laminar inclination angles,and to investigate the effects of solution p H and specimen inclination on the mechanism of tuff dissolution damage.The study shows that the surface of the chert produces"dissolution zone"after dissolution,combining with the macroscopic surface characteristics of the chert and electron microscope scanning analysis,it can be seen that at the early stage of soaking,the dissolution of the chert occurs at the laminae and non-laminae,but with the increase of soaking time,there is dissolution of the remaining insoluble material Si at the laminae,resulting in the reduction of the dissolution at the laminae,and the later dissolution mainly occurs at the non-laminae;the physical properties of the tuff deteriorate as the acidity of the solution increases,and the existence of the dip angle makes the deterioration of the specimen anisotropic,and the p H of the solution has a greater effect on the deterioration of the properties of the tuff than the dip angle of the laminae.（2）Uniaxial compression and triaxial compression tests were carried out on tuffs before and after dissolution under various conditions.The results show that the stronger the acidity,the more significant the deterioration of the mechanical parameters and that the degree of deterioration is influenced by the angle of inclination;As the dip of the laminae increases,the modulus of elasticity and compressive strength of each specimen first decreases and then increases,with a’V’-shaped distribution;uniaxial compression damage of the tuffs at all dips shows splitting damage along the axial stress direction,while tension damage and shear damage along the slip of the laminae occur under triaxial compression.（3）The chemical and mechanical damage of the rocks were defined according to the indoor dissolution test and uniaxial compression test,and based on the rock damage theory and Weibull distribution,the damage evolution analysis was carried out on the loading process of the tuffs after different acid dissolution,and the transverse isotropic damage model of the laminated rocks was established,while the rock damage model considering the void compacting stage was established,and the theoretical curves were compared with the test curves for analysis.The results show that the established transverse isotropic damage model and the theoretical curve considering the pore compacting stage have good correspondence with the experimental results,indicating that the established transverse isotropic damage model and the damage model considering the pore compacting stage can better describe the densification characteristics of the laminated rock mass under triaxial compression loading and the pore compacting stage characteristics under uniaxial compression.（4）Based on the PFC^2D parallel bonding model,the change in pore space due to chemical solution dissolution is uniformly transformed into the change in radius multipliers in the bonding model,and the radius multipliers of the tuff model before and after dissolution with different acidity and different dip angles are solved into the model and simulated in uniaxial compression tests,and the simulated deformation process curves are consistent with the test curves,indicating that it is feasible to use the change in radius multipliers to respond to the chemical dissolution of the tuff.The study takes typical limestone as the research object,comprehensively analyses the mineral composition,microstructure,mechanical properties and permeability of laminated rock masses during chemical dissolution in acidic water,explores the anisotropic damage mechanism and evolution process caused by dissolution,and conducts scientific analysis and research on the deformation and damage of rock masses under the combined chemical-mechanical action,which can provide parameters for the evaluation of the engineering stability of rock masses in acidic water environment of abandoned mines.The study will provide parameters for the evaluation of the stability of rock masses in abandoned mines in acidic water environments.