Study On Deformation And Failure Behavior Of Red Sandstone Under Mining Stress Path

The exploration of underground activities and the exploitation of resources make the underground engineering in our country gradually turn to the deeper area,and the disasters brought by engineering activities are more and more frequent,causing a lot of economic losses and casualties.There are many engineering disaster problems,among which the most important factor is disturbance.The deep rock mass is in the state of three-dimensional hydrostatic pressure.With the mining of coal and rock,the surrounding rock of the front working face has experienced a complex process of axial stress increase and confining pressure decrease.Xie Heping proposed three different mining methods,namely no coal pillar mining,caving mining and protective layer Mining,corresponding to different loading and unloading paths in laboratory experiments.In the underground mining activities,different mining methods cause different deformation,strength and crack failure modes to the surrounding rock,and then cause the falling off of the surrounding rock and the spalling of the surrounding rock,which leads to underground engineering disasters.In order to reasonably solve the disasters caused by the underground engineering activities,we should understand and be familiar with the differences between different mining methods and the deformation and failure of the surrounding rock under the influence of different mining methods Bad mechanisms are very important.In this paper,red sandstone is selected as the research object,and TAW-2000 electro-hydraulic servo testing machine is used to carry out conventional uniaxial and triaxial compression tests and rock failure mechanics tests under different mining methods.The evolution rule of average rotation angle with stress and strain under conventional loading and different mining methods is analyzed;the relationship between fractal dimension and rock fracture surface and failure strength is studied by using fractal dimension and block fractal dimension;the constitutive relationship based on average rotation angle is established by combining elastic mechanics,rock mechanics,continuum mechanics and damage mechanics.Through the research of this paper,some progress has been made as follows:(1)Confining pressure has a great influence on the deformation and strength of red sandstone.In the case of low confining pressure,the strain softening modulus of red sandstone sample is small and its brittleness is strong.With the increase of confining pressure,the ductility of red sandstone sample increases;the axial deformation is related to confining pressure,and increases with the increase of confining pressure.In the case of confining pressure,the transverse deformation and volume deformation increase obviously,but increase first and then decrease with the increase of confining pressure;the residual strength after peak is in the positive phase with red sandstone In the case of no confining pressure,the failure mode of red sandstone specimen is mainly tension crack,and accompanied by multiple shear cracks.When confining pressure exists and gradually increases,red sandstone gradually presents a single macro shear crack.(2)The strain softening modulus is the largest and the ductility is the strongest under the condition of no pillar mining,and the strain softening modulus is the smallest and the brittleness is the strongest under the condition of caving mining;the transverse and volume deformation of caving coal,protective layer and no pillar mining increase in turn,while the axial deformation is the largest under the condition of protective layer mining,the smallest under the condition of caving mining,and the compressive strength under the condition of caving mining The angle between the crack and the axial stress direction of the red sandstone sample is the largest under the mining mode without coal pillar,and the minimum under the mining mode of the protective layer.The number of cracks of the red sandstone sample under different mining modes is less than that of the conventional compression test(3)The larger the fractal dimension of the fracture surface is,the more brittle the red sandstone specimen is,the larger the transverse deformation and volume deformation when the axial stress reaches the maximum,and the largest fractal dimension of the fracture surface of the red sandstone specimen under the coal pillar free mining mode,at this time,the angle between the crack and the axial stress direction of the specimen is the largest;the higher the fractal dimension of the block degree is,the greater the peak strength and the greater the degree of the failure of the red sandstone is,and the more severe the failure is Under the same confining pressure,the block fractal dimension is the largest,the protection level is the smallest,and the larger the block fractal dimension is,the larger the strain softening modulus,lateral and volume peak deformation are.(4)Based on the theory of finite deformation mechanics,the relationship between the average rotation angle and the stress and deformation in the whole process of red sandstone is studied.Taking the average rotation angle as an internal variable of the constitutive relationship,the constitutive relationship between the average rotation angle and the internal deformation and rotation in the whole process of red sandstone is established.In the initial compaction stage,the slope between the average rotation angle and the stress and strain increases greatly.After entering the elastic stage,the average rotation angle falls down.In the yield stage,the average rotation angle begins to increase rapidly.At this moment,the internal cracks of the rock increase rapidly,and the local rotation and deformation increase rapidly.The average rotation angle in three different ways will have a very high value at the initial stage of the release of the confining pressure In the steep sliding stage,the sudden decrease of confining pressure causes the gap between the mineral particles to increase rapidly,which makes the original local deformation to recover and causes the average rotation angle to drop rapidly.