Study On Damage Mechanical Behavior Of Variable-angle Fractured Granite After Thermocycling

With the continuous development of society and economy,human engineering activities have gradually expanded to deep underground.Under the effect of ground temperature gradients,various types of rock engineering are facing higher and higher temperatures,and some rock engineering will also face frequent thermocycling.Considering the geological origin of rock materials or the special needs of certain projects,defects such as joints and cracks are unavoidable in the interior.The physical and mechanical properties of fractured rocks after thermocycling will be very different from those of intact rocks under natural conditions,and their damage evolution characteristics will directly affect the stability of the entire rock engineering.Based on this background,this paper comprehensively uses laboratory experiments,theoretical analysis,and numerical simulation to study the damage mechanical behavior of variable-angle fracture granite after thermocycling.The following research results have been achieved:?1?With the help of MXQ1700 box-type atmosphere furnace,high-precision electronic scale,electronic vernier caliper,cylindrical vacuum saturation container,HC-U81 ultrasonic monitor and Hot Disk thermal constant analyzer,the effects of the number of thermocycling on the macrophysical parameters such as diameter,height,volume,porosity,saturated mass,dry mass,density,longitudinal wave velocity,thermal conductiveity,and thermal diffusion coefficient of granite were obtained.With the help of MTS816 electro-hydraulic servo rock mechanics experimental system,the influences of the number of thermocycling and the dip angle of prefabricated flaw on the total stress-strain curve,uniaxial compressive strength,crack initiation stress,damage stress,elastic modulus,deformation modulus and peak strain of granite were obtained.?2?Using X-ray diffractometer and scanning electron microscope?SEM?,the effects of the number of thermocycling on the mineral composition and microstructure of granite were obtained,and the damage mechanism of granite caused by the thermocycling was analyzed.Based on the acoustic emission characteristics of granite under uniaxial loading,the influences of the number of thermocycling and the dip angle of prefabricated flaw on the damage characteristics of granite under load was analyzed.?3?Based on the statistical strength theory and the basic principles of continuous damage mechanics,the damage evolution equation and constitutive equation of granite considering the meso-defects caused by thermocycling are established and its validity is verified;According to the expressions of rock damage variables considering macroscopic defects given by relevant scholars,combined with the Lemaitre strain equivalence principle and continuous damage mechanics principle,the damage constitutive equation of granite considering the coupling effect of macro and micro defects is established and its validity was verified.?4?With the help of PFC^2D numerical simulation software,a numerical model for characterizing fractured granite was constructed by deleting particles.Based on a series of macro and meso parameter studies on the initial numerical model,the calibration of the meso parameters of the numerical model is completed.Finally,according to the established numerical model,the evolution characteristics of meso cracks and bond chains in the process of progressive failure of variable-angle fractured granite are analyzed.This paper includes 55 figures,14 tables and 79 references.