Study Of Unload Creep Properties Of Sandstone And Energy Evolution Analysis

Deep rock in high stress state,the deformation energy storage itself is high,exploitation of underground mineral resources and underground engineering excavation are a deep rock mass deformation energy release process,and the excavation surface is the potential energy release direction,so this is a typical unloading process.At the same time the compressive properties of rock is far greater than its tensile strength,expansion during unloading deformation in different directions and different mining face,is the dominant factor causing the damage of surrounding rock,the surrounding rock supporting for later corresponding nursing.Because of the difference of mining methods and machinery of the surrounding rock unloading status is not the same,leading to expansion deformation of surrounding rock deformation control supporting the myriads of changes,if improperly,may cause landslides and other accidents;to the safe and effective excavation of underground tunnel and underground mining of mineral resources,it is necessary to carry out further study on the creep characteristics of roadway surrounding rock unloading.In this paper,Fuxin Hengda coal mine roadway surrounding rock(sandstone)as the research object,by using TAW2000 rock mechanics testing system research on unloading creep mechanism and three axial compression test in energy evolution,through the introduction of the principle of minimum dissipation of energy from the energy point of view to study the rock during the process of unloading creep damage characteristics and damage,provide a basis for the design of the roadway surrounding rock in deep excavation engineering,the main conclusions are as follows:(1)In the three axial compression test,the axial,radial and volumetric strains increase with the confining pressure,and the stress-strain curves tend to be smooth near the peak,and the strain has no obvious peak in the unloading test.In the unloading test,the radial deformation of specimen from the elastic stage increased rapidly,the growth rate is far greater than the axial strain rate of rock specimen deformation by compression conversion for expansion,and peak strain corresponding to the starting point of the expansion.(2)The sandstone under loading unloading confining pressure is greater than the cohesion C test and unloading test of fixed axis confining the C value of less than l axial unloading confining C;sandstone in the loaded state is smaller than the internal friction angle of unloading confining pressure,and unloading test in fixed axis confining phi value must be greater than l thevalues of axial unloading;consists in loading test on rock failure to shear failure and tensile failure.Failure to unload and load test,the tensile failure is more obvious than C shear C value is small,and the compression shear failure surface relative tensile failure surface is smooth,the larger under load the former leads to sliding,the internal friction angle is smaller.(3)Unloading tests under different failure conditions,the first level load in the initial confining pressure under the action of three,consistent with the uniaxial loading test changes;but after the three grade in the unloading test,deformation or creep deformation,the axial and radial direction relative to the loading test on the increase of approximately 5%,visible unloading confining pressure tests and the deformation ability of unloading test,deformation ability was stronger than the three axial loading test.(4)By introducing damage evolution equation,a nonlinear creep damage model is established,and the evolution law of creep process of sandstone is described.The comparison between the sandstone creep test curve and the model curve shows that the damage evolution equation derived from the energy dissipation theory is basically consistent with the creep damage deformation law of the rock.(5)The initial loading force moment of rock work most of the process internal elastic energy storage,but also a small amount of dissipated energy release of rock from outside the total absorbed energy,elastic energy and dissipated energy are increased with the passage of time,the total energy and elastic energy increased faster;the peak point to the maximum,but this time due to the crack in rock and holes began to expand development,for the energy dissipation began to increase sharply;on the other hand,in the unloading confining pressure tests,and not from the peak point of unloading,but began to unload at the peak of 80%~90%,the confining pressure suddenly reduced gradually lead to an increase in radial deformation and crack of rock.Empty development consumes more energy;in the subsequent project due to crack and cavity development are more intense and macroscopic cracks and through failure surface,the A large amount of energy is released.