| In the process of mine mining,different mining rates and water inrush problems are easy to cause changes in the structure of the rock mass,and the closure and opening of internal cracks will inevitably cause the deformation of the rock mass,which not only weakens the mechanical properties of the surrounding rock mass of the roadway,but also easily causes the permeability of the surrounding rock mass to change,and then it is easy to cause accidents such as water inrush in the roadway and unstable damage of the surrounding rock of the roadway.In this paper,the mechanical properties and seepage characteristics of sandstone in the surrounding rock mass under high water pressure and stress unloading rate are studied,and the deformation and permeation law of sandstone under different stress unloading rate-seepage action are explored by combining indoor test and numerical verification,which provides a certain basic theory and basis for the prevention and control of water inrush accidents in coal mines and the study of instability and failure of surrounding rock in deep roadways.The main conclusions reached are as follows:(1)The axial strain of sandstone gradually decreases with the increase of confining pressure unloading rate,and the growth rate of axial strain gradually increases with the increase of confining pressure unloading rate.The axial strain and axial strain growth rate gradually decrease with the increase of the axial pressure unloading rate.The axial deformation of sandstone is slightly more affected by the axial pressure unloading rate than the confining pressure unloading rate.(2)In the early stage of stress unloading,the ringing count rate and energy rate are high,the specimen is in the elastic deformation stage,the ringing counting rate and energy rate continue to increase,when entering the failure stage,the energy stored in the elastic and plastic stage is released,the ringing counting rate and energy rate reach the peak,and after entering the softening stage,the acoustic emission signal decreases sharply.(3)The permeability growth rate of sandstone in the failure stage and the undamaged section of the same rate of 0.01MPa/s unloading and loading axial compression process differs by 5.24 times;For the damaged sandstone,the permeability generally decreases first and then increases with the decrease of the volume stress,and the permeability of sandstone in the linear elastic stage increases linearly with the decrease of the volume stress.(4)In the process of confining pressure unloading,the cross-sectional area of the specimen is restored from the compressed state to the unpressurized state,the pores and fractures expand,the seepage channel becomes larger,the permeability increases,and the permeability and permeability growth rate all increase and then decrease at the same time with the increase of the confining pressure unloading rate.In the axial pressure unloading process,the cross-sectional area of the specimen gradually increases at the same time with the decrease of the axial pressure unloading rate,resulting in a large number of pores and fracture structures inside the specimen at the same time and a larger volume,and the permeability and permeability growth rate generally show a trend of gradual increase with the decrease of the axial pressure unloading rate.(5)The relationship curve between permeability and stress solved by COMSOL matches well with the relationship curve between permeability and stress obtained by the experimental results,and the correlation coefficient is high.From the simulation analysis of sandstone deformation performance: the deformation of the specimen gradually increases with the increase of time;Under the same confining pressure unloading rate,the displacement increase that occurs when the specimen is deformed gradually increases with the decrease of the axial pressure unloading rate.From the simulation analysis of the seepage performance of sandstone,the initial stage of confining pressure unloading was in the fracture compaction stage,the permeability rate was the smallest,the seepage rate showed a gradient distribution from top to bottom,and gradually increased in the direction of seepage.Under the same confining pressure unloading rate,the seepage velocity gradually increases with the decrease of axial pressure unloading rate at the same time.The amplitude of velocity increase before and after the percolation velocity mutation point is 6 orders of magnitude.The paper has 48 figures,14 tables,and 87 references. |
