Damage Mechanism Of The Sandstone Under The Coupling Actions Between Cycle-impact Loading And Chemical Corrosion

Mechanical and chemical are the two main effects inside the Earth.In the process of blasting and excavation of complex geological conditions,engineering rock mass not only bears the cyclic impact load under one-dimensional or three-dimensional static stress such as the self-weight and structure of the original rock,but also suffers from chemical corrosion in the complex environment for a long time,which causes rock mineral composition and the change of stratum rock structure changes the physical and mechanical properties of rock.The coupling effect of mechanical and chemical corrosion greatly affects the long-term stability of engineering rock mass with complex geological conditions.The study of mechanical properties of rock under the coupled action of mechanical and chemical corrosion has become one of the hot research topics in the field of rock mechanics.Using the improved Hopkinson pressure bar(SHPB)combined with one-dimensional stress wave theory,a series of loading tests concerning different axial pressure cyclic impact were carried out on sandstone soaked in the chemical solution by taking the sandstone as the research object.The evolution characteristics of rock strength deterioration,failure mode and impact fractal under the coupling action of cyclic impact load and chemical erosion are analyzed.Meanwhile,the dynamic mechanical property deterioration and damage evolution law of rock damage are clarified.Scanning electron microscopy(SEM)was adopted for exploring the microstructural characteristics of rock mass under the coupling action of impact load and chemical erosion as well as the evolution of crack fracture process.In addition,based on the Weibull statistical distribution theory,the influence of the difference of rock mass fracture fractal characteristics under cyclic impact loading is investigated.Finally,the fatigue damage mechanism of sandstone under cycle impact loading and chemical corrosion is revealed.The main research contents and conclusions are presented as follows.According to the obtained test results,in the process of sandstone soaking in solution,minerals such as quartz,feldspar,and clay undergo complex physical interactions and chemical reactions with the solution,causing changes in the mineral composition and structure of the sandstone as well as the deterioration of indicators such as uniaxial compressive strength and solution p H.When the specimen is eroded by the solution,the total number of cyclic impacts and the dynamic compressive strength it can bear present a decreasing trend with the acid-base polarization of the solution.Through the fracture on the inner side of the specimen,the microstructure characteristics of the longitudinal section and the stress state of the specimen impact,it can also be confirmed that the roughness and unevenness of the structural surface of the specimen are mainly caused by the dissolution and corrosion of minerals resulted from chemical solutions.At the same time,the double broken cone state is damaged.The mode refers to the failure caused by insufficient shear resistance of the oblique section,and the "X" conjugate-like failure is mainly tensile shear failure.Finally,based on the RosinRammler distribution function,the fragmentation distribution law of sandstone under impact load is explored,and the relationship between fragment size,fractal dimension and fragmentation degree under different impact velocities is also obtained.