| The initial stress field is disturbed by underground mining,which causes the redistribution of stress,and then determines the way of roadway support and the layout of gas drainage borehole.To this end,this paper to Sichuan Furong Group Industrial Co.,Ltd.Baijiao coal mine 2481 face as the research background,first of all,using the self-developed “Large multi-field coupling coal and rock mining simulation test device”,the evolution of coal-bed strata stress-fissure field is studied under the condition of true three-dimensional mining stress.The self-made triaxial servo-controlled seepage equipment for thermo-hydro-mechanical coupling of coal containing methane was used to study the mechanical and permeability characteristics of coal containing methane based on the influence of the different loading-unloading speed,and a new method of unloading and unloading experiment on sandstone specimen was used to simulate the dynamic stress change of mining stress.Based on the above experiments,the following main research results can be obtained:(1)The vertical stress of roof increases and the horizontal stress of roof fluctuation decreases before the mining,and the vertical stress is decreased obviously and the horizontal stress is obviously increased after the mining.With the increase of the depth of floor rock,the crack quantity of the bottom plate is reduced,the longitudinal penetration capacity of the cracks is weakened,the bending deformation of the floor is reduced,and the range of the bottom plate is reduced.The bottom plate generally presents the characteristics of “middle high on both sides of the low”,and the bottom plate presents the “elliptical” shape along the strike direction.(2)The strength of coal samples under different loading-unloading speed conditions increased logarithmically along with the increasing initial hydrostatic stress and decreased along with increasing mining velocity which presents the power function relationship;The priority of failure forms of loading-unloading coal samples are shear,but some of them are tenso-shear composite;The change rule of the permeability of loading-unloading coal samples does not all decrease first and then increase as “V”.Under the tenso-shear composite failure form,the change rule of the permeability are properties that the increasing after a decrease is followed by a declined stage around the peak point and will rapidly become a new increase as “W”.Compared with the coal sample which does not contain methane,the strength of coal containing methane is lower,the axial strain is smaller when it fails,the rate of deformation modulus is bigger at the moment of failure,the phenomenon of dilatancy is more obvious.(3)Following the alternating loading-unloading test,the stress-strain curve moved on like waves,the waves' volatility decreases and then increases,near the ultimate strength,volatility is the biggest,the stable of waves' volatility increased along with the increasing initial hydrostatic stress;The damage variable of alternating triaxial loading-unloading test increased with the decreasing initial rate of alternating loading-unloading test and decreased with the increasing initial hydrostatic stress;the similarity of stress-strain curve between conventional loading-unloading test and alternating loading-unloading test increased along with the increasing initial hydrostatic stress and increased along with the increasing initial velocity of alternating loading-unloading.Along with the increasing initial hydrostatic stress,The rule of failure forms of loading-unloading sandstone samples are tensile ? tensile-shear composite ? shear.The degree of failure forms increased along with increasing loading-unloading velocity.(4)The effect of different excavation speed on the mechanical properties of rock mass can be studied by alternating loading and unloading experiment.The initial velocity of alternate loading and unloading experiment is better when the alternate speed is larger. |
PDF Full Text Request