Study On Creep Damage Characteristics Of Carbonaceous Shale Under Freezing And Thawing

With the strategic advancement of the western construction in our country,highway construction has become an important bridge and link for the development of central and western China.Carbonaceous shale is widely distributed in the Permian,Triassic and Devonian strata in central and western China,The development of qualitative shale stratification is obvious and easy to soften and disintegrate,which makes the slope along the slope vulnerable to instability and landslides and other disasters.therefore,this paper mainly analyzes the carbonaceous shale from the carbonaceous shale by the freeze-thaw cycle and the creep effect.Through the rock test and theoretical research methods,numerical analysis and so on,considering the multi-factor comprehensive impact of carbonaceous shale damage,The theoretical model of creep damage of carbonaceous shale under different freezing and thawing times is established,which provides the theoretical basis for the study of stability of carbonaceous shale slope.The following research results are obtained in this paper:(1)Through the X-ray diffraction analysis,the carbonaceous shale mineral composition was analyzed,and the hydraulic and carbonaceous shale hydraulic and mechanical properties under the freeze-thaw cycle were studied.The research shows that carbonaceous shale contains higher hydrophilic mineral montmorillonite,which is the main factor that causes rock to weather and weathering.with the increase of the number of freeze-thaw cycles,the mass loss rate and volume growth rate of carbonaceous shale increase correspondingly,and their mechanical strength parameters are deteriorating continuously.(2)Scanning electron microscopy study of carbonaceous shale structural deterioration,studies have shown that:with the increase of the number of freeze-thaw cycles,a small amount of microporosity and lamellar debris appeared on the surface of rock samples,and the micropore cracks of rock gradually deepened with the increase of the number of freeze-thaw cycles,The cycle increases the damage to the rock sample;By scanning electron microscope scanning binary image quantitative analysis can be found:with the increase in the number of freeze-thaw cycles,the surface area of carbonaceous shale samples accounted for The ratio of total area increased gradually,and the apparent damage of rock showed a significant increase trend.(3)The results of NMR experiments show that the porosity of rock samples increases with the increase of the number of freeze-thaw cycles,and the pore radius also expands correspondingly,and the proportion of pores with small pores always remains at a relatively large value;Through the pseudo-color image processing,the cracks in the initial hole of the rock sample are well developed.The pore fissures tended to expand with the increase of the number of freeze-thaw cycles.The damage of the rock sample became more pronounced with the increase of the number of freeze-thaw cycles.(4)Through the carbonaceous shale compression creep test,the creep damage equation which reflects different stress and time effects is established.The results show that:the carbonaceous shale samples exhibit significant phasing and viscoelastic properties under the loading stress at all levels.With the increase of stress and acting time,the nonlinear characteristic of rock creep damage is obvious.(5)Based on the rheological damage mechanics theory,the creep damage model of carbonaceous shale under the freeze-thaw cycle was established.The results show that the axial strain of carbonaceous shale with the freeze-thaw cycles is proportional to the number of freeze-thaw cycles,And the time increases,and the rock mechanics properties are obviously deteriorated.The established creep model can well reflect the phenomenon that the model parameters deteriorate with the increase of the number of freeze-thaw cycles,stress and time.