Experimental Research On Mechanical Properties And Creep Constitutive Model Of Ice-filled Fractured Red Sandstone

In recent years,freezing method has been widely used in construction of mines in northwestern region of China.Research on mechanical properties of frozen rock masses is gradually becoming a research hotspot.This paper takes Shilawusu mine and Xiaojihan mine shaft freezing engineering in the northwest of China as background,and takes typical red sandstone in water impregnated aquifer(100~300m)around wellbore as research object.Triaxial compression test of artificial ground ice was carried out by using a frozen soil triaxial test machine.Theory of rock mechanics,classical elastic mechanics and elastoplastic mechanics were used to analyze single and triaxial compression strength and deformation characteristics of freshwater ice under different sizes and loading rates.Also,failure modes of columnar ice samples at constant loading rate were studied.We comparatively analyses rules of freshwater columnar ice and polycrystalline ice intensity with confining pressure and temperature change.A failure criterion and a constitutive equation suitable for freshwater ice were proposed.The status of rock triaxial test systems was summarized.Based on existing equipment defects and research characteristics of this paper,a dynamic disturbance subzero rock triaxial testing system was independently developed.The system can carry out conventional uniaxial compression test,triaxial compression test,uniaxial loading and unloading rheological test,triaxial loading and unloading rheological test under different ambient temperature and different disturbance loads.Triaxial compression test under different temperature and different confining pressure for complete,ice-interrupted single-fracture and ice-interrupted double-fracture red sandstone(original rock)was carried out by using dynamic disturbance subzero rock triaxial testing system.The mechanism of ice body on strength,deformation and failure characteristics of frozen rock mass was analyzed by ice-rock macroscopic and meso-structure.Combined with the acoustic emission monitoring information during the triaxial compression process of rock mass,the relationship between whole process of damage and damage of ice-bearing fractured rock and acoustic emission characteristics was revealed.The frost heaving force test of ice-fracture red sandstone was carried out by using frost heaving test system.The typical frost heaving force evolution process of fracture-containing crack samples was obtained.The effects of temperature,crack width,trace length and penetration rate on the frost heaving force of fissure ice bodies were studied.And coupling mechanism between frost heaving damage and ice rock cementation on ice-fractured rock mass was discussed.By analyzing variation characteristics of acoustic emission energy during evolution of frost heaving force of fractured red sandstone,the damage degradation effect of frost heaving force on fractured rock mass was verified,and it pointed out that frost heaving effect causes obvious crack propagation at the end of fracture,the rock was vertically tensely damaged.At present,it is rare to study creep properties of rock mass under low temperature conditions.We used dynamic disturbance subzero rock triaxial testing system to carry out triaxial loading and unloading creep and triaxial loading creep perturbation test for single-fracture and layered joint rock samples.Triaxial creep properties and deformation and failure characteristics of frozen single-fracture and frozen layered red sandstone were studied,and influence of dynamic disturbance on rock creep was analyzed.By introducing soft-matter elements and nonlinear creeps,a nonlinear creep model was proposed,and creep constitutive equations of this model under one-dimensional and three-dimensional stress states were derived.Parameter identification was also finished by using data of triaxial loading creep test and triaxial unloading confining creep test.Then parameters of this model were obtained.The reliability and validity of the model were verified.And influence of stress level,crack inclination angle and structural plane inclination on fitting parameters was analyzed.Taking the creep data of frozen layered red sandstone as example,by comparing the model with classical Nishihara model and improved Nishihara model,the new model is more superior in describing the initial phase and the nonlinear creep phase.The results are instructive to supporting time,nonlinear deformation prediction,and safety evaluation of frozen rock wall during shaft sinking by freezing method in stratified rock strata in northwest China.And influence of orders of fractional differential and nonlinear viscous coefficient on initial creep phase and nonlinear creep phase were discussed.The long-term mechanical properties and nonlinear creep characteristics of frozen rock mass in northwest China were revealed.