Study On Fracture Evolution And Strength Degradation Of Silty Mudstone Under The Action Of Alternating Humidity And Heat

Silty mudstone is a sedimentary type of expansive soft rock,concentrated in southern China.Its main components include quartz,illite,montmorillonite and feldspar,etc.It has the characteristics of thermal expansion and contraction,dry contraction and wet expansion.The summer in the southern region is hot and rainy,and the temperature and humidity of the rock mass fluctuate frequently in time and space.After repeated wet-heat cycles,the rock mass will continuously exchange water and heat,which will cause the internal stress concentration of the rock mass,resulting in the formation,development and expansion of internal micro-cracks,which will lead to the deterioration of the rock mass strength.In view of this,this paper analyzes the crack evolution law of silty mudstone and the strength deterioration law of silty mudstone under different crack rates through different laboratory tests through laboratory tests,and demonstrates the test results in combination with the existing rock strain softening model The main research contents and conclusions are as follows:(1)By carrying out tests on the composition and basic physical properties of silty mudstone,the physical parameters such as ultrasonic longitudinal wave velocity,dry density,particle density,porosity,water absorption and saturation water absorption of silty mudstone were obtained.The silty mudstone was screened and sampled,and the screened samples were subjected to ultrasonic longitudinal wave velocity test,X-ray diffraction analysis,dry density test,particle density test and water absorption test,and the ultrasound of silty mudstone was obtained.Physical parameters such as longitudinal wave velocity,composition,dry density,particle density,water absorption rate and saturation water absorption rate(2)The self-developed temperature and humidity integrated device was used to test the crack evolution of silty mudstone after different humidity and heat cycles,and combined with CT scanning and image processing technology to obtain the processed crack CT image,using AVIZO and Image-Pro Plus(IPP)software obtains three-dimensional reconstruction images and fracture parameters of fractures,and then extracts parameters such as total fracture length ratio,fracture rate,average width,fractal dimension and dip angle,and analyzes the number of wet-heat cycles and different sections of silty mudstone Law of crack evolution at depth.(3)The dry and wet cycles and CT scanning tests were used to obtain fissures of different developmental degrees,and the uniaxial and triaxial compression tests were carried out on silty mudstones with different fissure rates.According to the test results,the silty mudstones under different fissures were obtained.The deterioration law of parameters such as axial compression strength,tangent modulus,peak strength,elastic modulus and shear strength.(4)Combining the strain softening damage constitutive model of the fractured rock mass,the triaxial compression test results of the fractured silty mudstone were verified,and the accuracy of the triaxial test results of the fractured silty mudstone was demonstrated.