Experimental Study On Rock Deformation Characteristics And Surface Deformation Localization Under Different Loading Rates Based On DIC Technology

The instability and failure of engineering rock mass are often caused by the excessive deformation of rock mass.In the process of deformation and failure,the deformation of rock mass gradually changes from the initial uniform to non-uniform,resulting in strain concentration.When the strain concentration accumulates to a certain extent,one or more deformation narrow bands,that is,the deformation localization band,will eventually lead to the instability and failure of rock mass.In order to further study the deformation and failure process and mechanism of rock under complex stress environment,this paper,combined with digital image correlation(DIC)technology,has carried out triaxial compression tests under different loading rate,different water cut state and different confining pressure conditions,and studied the deformation and local failure characteristics of rock under different test conditions.The main conclusions are as follows:(1)Under different conditions,the evolution of the cloud map of the deformation field of the rock is roughly the same,that is,the color of the cloud map before the peak is more consistent,the deformation of the rock surface is more uniform,and the strain concentration begins on the cloud surface near the peak point,and finally a clear deformation localization zone occurs.The deformation localization zone of sandstone is regular strip-shaped,and the deformation localization zone of tuff has no fixed shape,and with the increase of the loading rate,the width of the rock deformation localization zone is increasing.(2)By arranging virtual strain gauge in the observation area,the stress-strain curve is obtained.From the curve analysis,it can be seen that at the initial stage of loading,the curve basically coincides,indicating that the deformation of rock surface is relatively uniform at this stage,and the curve begins to separate near the peak point,the rock surface begins to produce non-uniform deformation,and the curve separation phenomenon after the peak is more significant,the strain passing through the deformation localization belt increases rapidly,and the strain not passing through produces rebound phenomenon.(3)The peak strength,modulus of elasticity,Poisson's ratio and loading rate of sandstone show a good linear growth relationship under different water cut conditions;the peak strength,modulus of elasticity,axial strain,radial strain and volume strain of tuff under different confining pressure all show a good linear growth relationship with loading rate;the peak strength and modulus of elasticity of sandstone(brittle failure)The peak axial strain and peak radial strain of tuff under the field are more sensitive to the loading rate than that of sandstone.(4)Virtual strain gauge is arranged inside and outside the deformation localization zone to measure the strain inside and outside the zone,and the bifurcation point of the strain difference is obtained after the difference operation,then the starting stress and the starting stress level of the axial and radial deformation localization of the rock are determined.With the increase of water content,the starting stress decreases,and the starting point is gradually advanced.