Dynamic Mechanical Properties And Damage Model Of Freeze-Thaw Fractured Rock Mass

With the development of national infrastructure construction and the promotion of the Belt and Road Initiative,the number and scale of construction projects in cold regions are increasing,and freeze-thaw disasters have become the primary issue affecting the construction of projects in cold regions.In practical engineering,rock mass not only has many natural initial damages such as cracks and joints,but also bears more and more complex loads,including dynamic loads such as impact,blasting and earthquake.Therefore,to reveal the influence of freeze-thaw damage,crack damage and dynamic load damage on the mechanical effects of rock mass strength,deformation and damage,this paper carried out the freeze-thaw cycle test and impact compression test of intact and crack red sandstone to study its dynamic mechanical behavior.Based on statistical damage theory and component model theory,the dynamic damage evolution equation and constitutive model of freeze-thaw rock are established.Then considering the influence of fracture damage,the dynamic damage evolution equation and constitutive model of freeze-thaw fractured rock mass are constructed.The main research contents and conclusions are as follows:(1)Complete rock samples under saturated condition and 0°,45° crack rock samples were subjected to freeze-thaw cycles.When the number of freeze-thaw cycles reached 0,10,20 and 40 times,four groups of SHPB impact compression tests under different strain rates were carried out to study the effects of fracture inclination,freeze-thaw cycles and strain rate on the dynamic failure behavior of rock mass.The test shows that the freeze-thaw damage process of rock is carried out from the surface to the inside,and the degradation modes can be summarized as particle spalling mode,flake spalling mode and block spalling mode.Under impact load,the overall trend of stress-strain curve of freeze-thaw fractured red sandstone is basically the same,which can be divided into three stages:elastic deformation stage,plastic deformation stage and damage and failure stage.The whole deformation and failure process shows obvious elastic-plastic deformation characteristics and viscous characteristics.(2)According to the whole process characteristics of rock SHPB impact compression deformation and failure,considering the non-uniformity of rock materials,based on statistical damage theory and component model theory,the dynamic damage constitutive model of freeze-thaw rock is established.The coupling effect of freeze-thaw damage and dynamic load damage and the macroscopic mechanical response induced by freeze-thaw damage are theoretically characterized,and the damage and failure mechanism of rock under different freeze-thaw cycles and strain rates are revealed.The results show that the combined action of freeze-thaw factor and dynamic load factor aggravates the total damage of rock,but its coupling effect weakens the total damage.The theoretical curve of damage model is in good agreement with the experimental curve,which can accurately describe the dynamic deformation and failure process of rock under the action of freeze-thaw cycle,and verify the reliability of the model.(3)Considering the influence of crack inclination angle,the freeze-thaw fractured rock mass under dynamic load is equivalent to the initial damage caused by prefabricated cracks and the total damage caused by freeze-thaw-dynamic load after prefabricated cracks.The dynamic damage evolution equation and damage constitutive model of freeze-thaw crack rock mass are established with crack inclination angle,freeze-thaw cycles and strain rate as control variables.The results show that the initial crack damage,freeze-thaw damage and dynamic load damage aggravates the total damage of rock mass,but the coupling effect of any two kinds of damage weakens the total damage.The nonlinear response and macroscopic deformation failure characteristics under the coupling effect of three kinds of damage are revealed from the perspective of microscopic damage evolution.The theoretical curve of the model is in good agreement with the experimental curve,reflecting the nonlinear characteristics of the coupling and mutual influence of freeze-thaw,cracks and dynamic load on the damage expansion of rock materials.