Research On The Damage Characteristics Of Carbonaceous Shale Under Freezing And Thawing

Carbonaceous shale is widely distributed in China's central and western areas of the Permian and Devonian strata,the underground rock stratum is exposed in the atmosphere after the excavation of the foundation pit or slope in these areas.It is easily weathered and disintegrated by complex climate and environment,So that the macroscopic physical and mechanical properties of rock are seriously deteriorated and the freezing and thawing disasters such as ground fissures,debris flows and landslides are induced.therefore,from the point of view of microstructure and physical mechanics in this paper,analyzing the microstructure and mechanical properties of carbonaceous shale under freeze-thaw cycles,establishing the damage evolution equation and the constitutive model of the frozen and thawed damage of carbon shale and revealing the mechanism of carbon and carbon shale freeze thaw damage by means of nuclear magnetic resonance(NMR),ultrasonic testing and mechanical compression test.The results have important theoretical significance to the protection of carbon shale cutting slope,and the following is the research results:1)The carbonaceous shale mainly contains quartz,zeolite and zinc manganese ore by means of X ray diffraction test,and the basic physical and mechanical properties of carbonaceous shale have been analyzed.2)Experimental study on mechanical damage characteristics of carbonaceous shale under cyclic freezing and thawing shows that the uniaxial compressive strength and elastic modulus of carbonaceous shale show exponential decay trend,the peak strain and Poisson's ratio have risen with the increase of the number of freeze-thaw cycles.3)Themicrostructure damage characteristics of carbonaceous shale are analyzed by nuclear magnetic resonance and ultrasonic testing,research shows that the T2 spectrum distribution,the spectral area and the porosity of the carbonaceous shale increased gradually,the P-wave velocity decreased with the increase of the number of freeze-thaw cycles,and he damage degree of the microstructure of the carbon shale reaches the maximum by establishing the damage evolution equation of microstructure based on porosity and acoustic wave when the number of freeze-thaw cycles reaches 400 times.4)The damage constitutive model of carbonaceous shale under freezing and thawing load is established by damage mechanics theory,and revealing the degradation mechanism of carbon shale in freeze-thaw damage combined with nuclear magnetic resonance images.