Mechanical Properties Of Muddy Red Sandstone Under Water Pressure With Loading And Unloading And Its Damage Deterioration Mechanism

When resource extraction or underground engineering construction is carried out in areas where red sandstone is widely distributed,the problem of excavation and unloading of red sandstone under water pressure is often encountered,which is prone to engineering accidents due to the characteristics of red sandstone such as easy disintegration and significant reduction in strength when exposed to water.These are mostly due to the lack of systematic mastery of mechanical properties and its damage deterioration mechanism during excavation and unloading of red sandstone under water pressure,which leads to it becoming a technical bottleneck restricting the safe and efficient construction and operation of underground resource extraction and engineering construction.Therefore,based on the Natural Science Foundation of Jiangxi Province project(No.20224ACB204020),this paper investigates the mechanical properties of muddy red sandstone under water pressure and its damage deterioration mechanism by combining indoor tests and theoretical analysis,taking the muddy red sandstone in the river crossing tunnel of Rong-Jiang Road IV as the research object.The main research contents and results of this paper are as follows:(1)The specimens of muddy red sandstone made were tested for basic physical indices and mineral composition content.Uniaxial and triaxial compression and unloading tests with different initial unloading levels were carried out to analyze and study the strength,deformation and energy conversion characteristics of the muddy red sandstone under no water pressure.The results show that the water content state,surrounding pressure and initial unloading level have a great influence on the strength,deformation and energy conversion characteristics of the muddy red sandstone.(2)The muddy red sandstone under water pressure was subjected to triaxial compression and unloading tests with different initial unloading levels,and the permeability of the rock was calculated using the steady-state method to obtain the changes of strength,deformation characteristics and permeability of the muddy red sandstone under water pressure.It was found that the strength and deformation resistance of the muddy red sandstone decreased with the increase of water pressure;the permeability of the rock showed a pattern of increasing and then decreasing with the increase of axial pressure;the peak permeability of the rock increased significantly during the unloading compared with the triaxial compression test;the larger the initial unloading level was,the smaller the peak permeability of the rock.(3)The macroscopic damage characteristics of muddy red sandstone under triaxial loading and unloading with and without water pressure were investigated,and the analysis showed that:the muddy red sandstone specimens showed tensile or tensile-shear damage;the greater the water pressure,the more obvious the brittle damage characteristics of the rock;the fracture of the rock was mainly caused by the combination of shear damage and partial tensile damage;the greater the initial unloading level,the more obvious the tensile damage.(4)Using scanning electron microscopy and X-ray diffractogram analysis,the changes of fine structure and mineral components of muddy red sandstone under different water-bearing states were investigated;through theoretical derivation,the effects of pore water pressure on the effective surrounding pressure and pure type I fracture of the rock were studied.The comprehensive research and analysis have obtained the damage deterioration mechanism of muddy red sandstone under water pressure.(5)The regression analysis between the data obtained from the tests and the four commonly used rock damage criteria was performed,and the D-P strength criterion was obtained to be a better fit.On this basis,the statistical damage principal structure model of muddy red sandstone with different initial unloading levels under water pressure was derived and established,and the principal structure model can better reflect the strength damage trend of muddy red sandstone with different initial unloading levels.