Mechanics and permeability characteristics of steep seam roof sandstone under disturbance stress

In order to study the problem of surrounding rock deformation and permeability characteristics caused by the change of vertical stress and horizontal stress during coal mining, a self-developed device Gas Containing Coal Fluid-solid-heat Coupling Triaxial Servo Permeability Experimental Device was used.Taking the sandstone sample from the roof of steep mine as study object, different initial stresses with a certain axial stress to the influence of deformation law and permeability characteristics of the failure stress during surrounding stress unloading was studied.The main results are:there exists a point during yield stage, which is the turning point of tension failure to compression and shear failure, the closer unloading point to yield strength, the stronger degree failure of sample; with the same surrounding stress (axial stress), the peak value of sandstone rock increases with initial axial stress (surrounding stress); the unloading amount percentage of sandstone rock failure decreases with the increase of axial stress; after sandstone rock unloading failure, peak gas flow has an exponential relation with volumetric strain; the main sandstone failure form appears as tension-shear mixture fissures along bedding, and the fissures are well developed, indicating there is a good relation with permeability characteristics and fissure develop degree.As far as concern, the permeability characteristics of rock are closely related to stress state it exists.Therefore, the research on deformation failure law and gas flow characteristic disturbance stress is very important to guide the layout of exploitation drill in steep coal mine and improve gas drainage efficiency.