| Most of the underground engineering rock mass is in a multi-field coupling environment.The change of seepage field and stress field caused by engineering disturbance will cause rock instability,and in the end rock mass engineering disasters will happen.In order to further study the effect of the coupling of seepage field and stress field on the deformation and failure of sandstone,the visual triaxial compression servo control test system independently developed and designed,which was used to carry out seepagestress coupling test under different confining pressure conditions and different drainage conditions.With the help of 3D digital image correlation technology,the whole cloud map of sandstone surface deformation field evolution can be obtained,and then the temporal and spatial evolution law,mechanical and seepage characteristics and deformation localization characteristics of sandstone surface deformation under different confining pressures and different drainage conditions are analyzed.The main research results obtained are as follows:(1)Reveals the temporal and spatial evolution law of sandstone surface deformation under the coupling action of seepage and stress.Under the coupling action of seepage and stress,the sandstone displacement field undergoes an evolution process from layered distribution to discontinuous displacement gradient,and the strain field undergoes uniform to non-uniform evolution,and an oblique shear-like strain concentration area is formed in the post-peak stage.The first 5 % The radial and axial strain points evolve from a diffuse distribution to two symmetrical oblique shear distributions,and the seepagestress coupling effect is mainly prominent in the post-peak failure stage.(2)The influence of different confining pressures and different drainage conditions on the deformation and failure of the sandstone surface is analyzed.With the increase of confining pressure,the smaller the strain concentration area on the sandstone surface,the smaller the aggregation degree of the first 5% strain points in space;under different drainage conditions,the strain concentration area on the sandstone surface under undrained conditions is larger than that under drainage,and the first 5% of the strain points are smaller in space.The distribution of strain points in space is more concentrated than that of drainage;under different drainage conditions,with the increase of seepage water pressure,the strain concentration area on the sandstone surface increases,and the first 5% strain points are more concentrated in space;compared The analysis shows that the confining pressure has a more significant effect on the temporal and spatial evolution of sandstone surface deformation than the seepage water pressure.(3)The evolution characteristics of mechanical and seepage characteristics of sandstone under different confining pressures and drainage conditions are compared and analyzed.With the increase of confining pressure,the peak strength of sandstone increases,the volume strain at the peak decreases,the elastic modulus and Poisson’s ratio increase continuously,the permeability decreases,and the time point of the maximum permeability,which all appear after the peak value,is delayed.Under different drainage conditions,the peak strength,volume strain at peak,elastic modulus and Poisson’s ratio of sandstone without drainage are larger than those with drainage.Under different drainage conditions,with the increase of osmotic pressure,the peak strength of sandstone decreases,while the volume strain,elastic modulus,Poisson’s ratio and permeability at the peak increase,and the maximum permeability appears earlier.With the decrease of the difference between osmotic pressure and confining pressure,the macroscopic fracture surface of sandstone samples gradually changes from a single oblique shear to a combinational tensile and oblique shear,and the meso-topography of the fracture surface changes from stepped to fog and then to mirror,and the failure gradually changes from transgranular cracks to intergranular cracks.(4)The evolution characteristics of sandstone deformation localization under different confining pressure conditions and different drainage conditions are analyzed,and the influence law of confining pressure and drainage conditions on the initiation stress and the level of initiation stress of sandstone deformation localization is revealed.Under the coupled action of seepage and stress,the smaller the confining pressure is,the more severe the increase of strain in the sandstone deformation localization zone is,and the more significant the strain unloading is outside the zone.The higher the starting stress of deformation localization is,the lower the starting stress level is,and the earlier the starting point is.Under different drainage conditions,the strain increase in the deformation localization band is more severe than that in the drainage,the strain unloading is more significant outside the band,the starting stress of the deformation localization is lower,the starting stress level is higher,and the starting point is earlier.Under different drainage conditions,the larger the osmotic pressure is,the more severe the increase of strain in sandstone deformation localization zone is,the more significant the strain unloading is outside the zone is,the lower the starting stress of deformation localization is,the higher the starting stress level is,and the earlier the starting point is. |
