| The area of China is vast,of which the frozen area accounts for more than 70% of the total land area,and rich in mineral resources.However,rocks in frozen areas generally face the serious problem of frost-thaw damage deterioration,and freeze-thaw disasters are more likely to occur under various static loads and impact loads.With the development of major strategic projects such as the implementation of western development successively unfolding in the cold area,it is of great significance to deeply understand the deterioration law of rock freeze-thaw damage and the mechanical characteristics under different loads to the safe development of resources in the cold area.In this paper,the rock mass engineering in the cold area is used as the research background,relying on the project,the apparent damage characteristics of freeze-thaw sandstone are first analyzed,and then the effects of freeze-thaw cycle and strain rate effect on rock mechanics and characteristics are studied from the two aspects of static mechanics and dynamics,and the macroscopic failure characteristics and energy dissipation law of sandstone under impact load are studied by introducing fractal characteristics and energy dissipation theory.The main research contents are as follows:(1)The physical properties such as apparent morphology,water-saturated quality,porosity and longitudinal wave velocity of sandstone samples in freeze-thaw test were measured and recorded,and after comparative analysis,it was found that the freezethaw damage mode of sandstone can be divided into flake mode and crack mode,and the degree of damage deterioration is related to the degree of force;the water-saturated quality and porosity increase with the increase of the number of freeze-thaw cycles,and the longitudinal wave velocity decreases accordingly.(2)Based on the 3D-DIC system,static uniaxial compression experiments were conducted to study the freeze-thaw cycle effect of sandstone under multi-stage strain rate loading,and to analyze the three-dimensional displacement field change of sandstone surface.It is found that there is a correspondence between the shear failure surface of the specimen and the concentration of the displacement field,the higher the strain rate,the greater the degree of failure of the specimen,and the closer the failure surface is to the center of the specimen;the deformation process of the sandstone surface is uneven and the local deformation is greatly different;the peak strength and elastic mold of the sandstone increase with the increase of the strain rate,and decrease with the increase of the number of freeze-thaws.(3)The impact test of freeze-thaw sandstone was carried out by Hopkinson pressure rod(SHPB)system,and the influence law on the dynamic mechanical properties of sandstone under the action of freeze-thaw cycle under high strain rate was obtained.The results show that with the increase of strain rate,the dynamic elastic modulus,peak stress and peak strain of sandstone gradually increase,and with the increase of the number of freeze-thaw cycles,the dynamic elastic modulus and peak stress of sandstone continue to decrease,and the peak strain does not change much.(4)The macroscopic failure characteristics and energy dissipation law of sandstone under impact load were analyzed by means of block degree analysis methods,fractal theory and energy dissipation theory.The results show that the average block size and fractal dimension of the fragments increase with the increase of the number of freeze-thaw cycles and the strain rate;under the joint influence of freeze-thaw action and strain rate effect,the sensitivity of the average block size of the sandstone fragments to one of the parties will weaken with the increase of the other side;with the increase of the number of freeze-thaw cycles and the strain rate,the degree of fragmentation of the specimen increases,and the energy absorbed by the specimen failure increases. |
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