| With the continuous growth of the economy and the ever-increasing demand for resources,shallow stratum resources are becoming increasingly scarce,making the development and utilization of deep underground engineering a necessary trend,especially in areas such as mining engineering,tunnel engineering,energy storage,and nuclear waste disposal engineering.During the excavation and support process of deep underground engineering(e.g.,underground workshops,water diversion tunnels,mining engineering,etc.),the surrounding rock experiences a loading and unloading stress process,from the disruption of stress balance to the redistribution of stress.The time-dependent deformation of fractured rock formations,formed under high-stress environments and influenced by loading and unloading stress paths,has become increasingly prominent in recent underground engineering construction in China,posing adverse effects on construction and long-term stability of the projects.Based on this,this study takes a deep chamber granite as the research object,and through indoor mechanical tests,simulates the loading and unloading stress paths caused by engineering disturbance to prepare loading fracture specimens and unloading fracture specimens,and conducts triaxial creep tests on them.This study explores the energy time-dependent evolution laws during the creep process of intact granite blocks,loading fracture specimens,and unloading fracture specimens.Based on the energy dissipation principle,damage variables are defined,revealing the time-dependent evolution characteristics of intact granite blocks and fractured rock masses.Combining experimental research with theoretical analysis,a creep model based on strain energy description under three-dimensional stress state is established from an energy perspective.The main research results of this paper are as follows:(1)Through conventional triaxial compression tests on intact granite blocks,loaded fracture specimens,and unloaded fracture specimens,the energy evolution laws and their differences in the whole deformation and failure process of intact granite blocks and fractured rock masses are revealed.Before reaching peak strength,the external energy of intact rock blocks is mainly converted into elastic strain energy,and the dissipation energy grows slowly.After the peak,the elastic strain energy is rapidly released,and the dissipation energy grows rapidly.Under lower confining pressures(5MPa,10 MPa,and 20MPa),the dissipation energy of the fractured rock mass exhibits a convex growth,while under higher confining pressure(30MPa),it exhibits a concave growth.The total energy,elastic strain energy,and dissipation energy at the peak points of intact rock blocks,loaded fracture specimens,and unloaded fracture specimens increase linearly,negatively exponentially,and positively exponentially,respectively,with increasing confining pressure.(2)Through triaxial creep tests on intact granite blocks,loaded fracture specimens,and unloaded fracture specimens,the energy aging evolution laws in the creep process of intact granite blocks and fractured rock masses are revealed.During the creep process,the creep failure stress and the absorbed total energy of intact rock blocks and fractured rock masses increase with increasing confining pressure.The total energy curves of intact rock blocks and fractured rock masses evolve in a manner similar to axial creep deformation during the creep process,both exhibiting stage characteristics similar to creep deformation.The elastic strain energy of intact rock blocks and fractured rock masses remains unchanged under different constant stress levels and is rapidly released when creep failure occurs.After experiencing a decay phase and a stable phase,the dissipation energy enters a sudden increase phase.(3)Based on the principle of energy dissipation,a damage variable is defined to reveal the damage evolution characteristics of intact granite blocks and fractured rock masses under the influence of stress and time.In the entire deformation and failure process of intact granite blocks,loaded fracture specimens,and unloaded fracture specimens,the dissipation energy increases with deformation,and the damage evolution characteristics are consistent with the energy dissipation evolution laws,continuously increasing with the increase of deformation.For intact rock block specimens,the volumetric turning point can be used as the starting point of significant deterioration of rock properties.During the creep process,the damage of intact rock blocks continuously increases with the passage of time under a constant stress level.For loaded fracture specimens and unloaded fracture specimens,when the stress increases to a certain value,the damage continuously increases with the passage of time under a constant stress level.(4)Based on the Burgers model,considering the non-linear characteristics of granite creep and the triaxial stress and strain states,combined with energy theory,a non-linear creep model based on strain energy description is established.In response to the non-linear characteristics during the creep process of intact granite blocks and fractured rock masses,a non-linear viscoplastic element is introduced based on the Burgers model to describe the accelerated creep stage characteristics of intact granite blocks and fractured rock masses.On this basis,combining with creep tests,the transverse and axial creep correlation is established to construct a granite non-linear creep model based on energy characterization. |
