Experimental Research On Mechanical Properties Of Gas Hydrate Bearing Coal Under Unloading Stress Path

To understand the strength and deformation characteristics of gas hydrate bearing coal under the different stress paths is the key for the application of coal and gas outburst prevention technology based on the hydrate method.Firstly,the self-developed integrated test device for gas hydration solidification and mechanical properties was used to carry out mechanical properties tests of gas hydrate bearing coal under different stress paths and to study the effects of stress paths,hydrate saturation and coal particle size on the strength and deformation of gas hydrate bearing coal.Then,the strength and deformation changes law of gas hydrate bearing coal under the loading and unloading test conditions are compared and analyzed.Finally,the mechanical properties of gas hydrate bearing coal are compared with those of the gas bearing coal to reveal the effect of gas hydration and solidification on the coal and gas outburst prevention from the perspective of the change of mechanical properties of coal.The triaxial test results of gas hydrate bearing coal under loading stress paths shows that the deviatoric stress-strain curve of coal hydrate containing gas hydrate is strain hardened,The greater the hydrate saturation of samples with the same pulverized coal particle size,the greater the failure strength and initial yield strength.When the hydrate saturation is the same,the smaller the pulverized coal particle size,the larger the failure strength and initial yield strength of the sample.Under the load stress path,the deformation modulus of gas hydrate bearing coal decreases rapidly with the increase of axial strain,then decreases slowly,and finally stabilizes;the Poisson ratio decreases first with the increase of axial strain,then increases and finally stabilizes.The triaxial test results of gas hydrate bearing coal under unloading stress path show that the greater the sample hydrate saturation,the longer the stress plateau stage,and the greater the residual stress,The greater the unloading confining pressure rate,the smaller the unloading confining pressure effect coefficient,and the more vulnerable the sample is to instability and failure.The deformation modulus always decreases during unloading,while the Poisson ratio always increases.Under the stress path of loading and unloading,the deviatoric stress-strain relationship curve of gas hydrate bearing coal almost coincides in the early stage of the elastic phase,and there is no significant difference.As the axial stress continues,the strain curve begins to deviate.Compared with the loading path,the radial deformation of the gas hydrate bearingcoal under the unloading path is larger,and the sample is expanded.The triaxial test results of gas hydrate bearing coal and coal containing gas under loading and unloading stress path show that the formation of gas hydrate in coal improves the failure strength and deformation resistance of coal,which provides a theoretical basis for the prevention of coal and gas outburst by gas hydration and solidification...