Damage Characteristics Of Weakly Consolidated Sandstone Based On Energy Evolution Characteristics

Coal resources as one of the important energy in our country,with the sustainable development of economy in our country present in short supply situation,the western region has become an important base of energy strategy in our country.However,widely distributed in the region of the Jurassic and cretaceous strata has obvious characteristics of weak cementation,because of the special rock mechanical properties research is still not enough.As a result,disasters and accidents occur frequently in the process of coal development,it is urgent to carry out in-depth research on its mechanical properties.This paper which takes the west weak cementation sandstone as the research object,the dry and saturated state under uniaxial cyclic unloading test and triaxle compression test,and pore structure characteristics before and after damage by nuclear magnetic resonance（NMR）test.At the same time,emphatically from the macroscopic and microscopic two directions to analyze this kind of deformation and failure characteristics of sandstone and pore distribution.The damage evolution law of dry and saturated sandstone under uniaxial cyclic loading was obtained by using accumulated dissipation energy.The damage evolution law of dry and saturated sandstone under uniaxial cyclic loading was obtained by using accumulated dissipation energy.The damage constitutive model of dry and saturated sandstone under triaxial compression was established by using energy method and Weibull statistical theory,and verified with experimental results.The results show that:（1）In the uniaxial cyclic loading and unloading test,both saturated and dry samples underwent 5 cycles of loading and unloading,and the elastic modulus and Poisson’s ratio were positively correlated with the cycles of loading and unloading.Under the same conditions,the elastic modulus and Poisson’s ratio of dry sandstone are larger than that of saturated sandstone either during loading or unloading.（2）Based on energy method,in triaxle compression test,the dry and saturated samples its energy storage ratio increases with axial strain decrease-in the trend of decrease,the curve trough position corresponds to the stress strain curve of crack stressσ_ci point,curveσ_f wave expansion and corresponds to the stress point,energy dissipation ratio with opposite curve law.There is a good linear relationship between the maximum value of total energy and dissipated energy of dry sample and confining pressure,a good quadratic function relationship between elastic energy and confining pressure,and a good linear relationship between total energy,dissipated energy and elastic energy and confining pressure of saturated sample.（3）The T₂ spectra of the samples before and after failure under different confining pressures were obtained by nuclear magnetic resonance test.Due to the difference of the primary pores inside the rock and the large discrete type,they could only be compared with the T2 spectra measured before their own failure.The results show that the total area of T₂spectrum increases in different degrees after the specimens are destroyed.Taking the sample with 6MPa confining pressure as an example,the first peak in T₂spectrum moved right and the second peak moved left after damage,and the signal intensity increased,indicating that some small holes radial medium aperture developed after damage and local fine fractures tended to be compressed.（4）Based on the accumulated dissipation energy,the damage D value of sandstone under uniaxial cyclic loading and unloading increases with the increase of cycles.The D value of dry sandstone damage variable ranges from 0.11 to 0.73,and that of saturated sandstone damage variable ranges from 0.10 to 0.70.（5）Based on the energy method and statistical theory,the constitutive model of weakly consolidated sandstone under triaxle compression is obtained and verified with the experimental curve.Figure[45]Table[17]Reference[73]...