Study On Evolution Mechanism Of Energy Damage And Self-inhibition Evolution Model Of Non-penetrating Jointed Sandstone

The accumulation and dissipation of rock mass energy can essentially reveal the whole process of rock mass deformation and instability in practical engineering.Exploring the influence of joint form on the damage and failure law of engineering rock mass from the perspective of energy can provide an important reference value for solving the stability problem of engineering rock mass fundamentally.At present,the research on rock energy mainly focuses on energy evolution characteristics of intact rocks and rocklike materials at the pre-peak,while the research on the energy evolution mechanism of jointed rocks in the whole loading process is less.Therefore,in this paper by using the indoor rock mechanics test,the digital image correlation method and particle flow numerical simulation technology,based on rock energy theory,the joint dip effect and length effect of the mechanical characteristics,macroscopic and mesoscopic mechanisms of energy and damage evolution and the energy self-inhibition evolution model about non-penetrating jointed sandstone were studied.The main research contents and achievements of this paper are as follows:(1)Experimental study on the mechanical characteristics of non-penetrating jointed sandstone under uniaxial compression shows that: as the increase of dip angle of joint,the main mechanical parameters of the jointed sandstone show an asymmetric “U” shape,and finally show collapse of tension-shear mixed failure,tensile-shear mixed failure,shear failure,and split failure in turn,and the area of initiation firstly increase and then decreases at the pre-peak;as the increase of length of joint,the main mechanical parameters of jointed sandstones and initiation range gradually decrease at the pre-peak,and eventually shear failure is the main factor;the evolution characteristics of the maximum principal strain at the prefabricated joint tip can reveal the initiation order of joint tip and the ultimate failure of rock samples form.(2)By analyzing characteristics of energy damage evolution of non-penetrated jointed sandstone during uniaxial compression test,we found that: the energy evolution process of jointed sandstone can be divided into five stages;as the increase of dip angle of joint,the difficult degree of failure of jointed sandstone driven by energy is difficulteasy-difficult.During the crack initiation,the degree of mutation damage and the extent of crack extension is firstly increased and then decreased,and the rupture degree is firstly decreased and then increased at the post-peak;as the increase of length of joint,joint sandstone is more susceptible to energy-driven damage,the degree of mutation damage and crack extension decreases during crack initiation,the cumulative damage increase at the pre-peak,and the rupture degree decreases at the post-peak.(3)Based on the evolution characteristics of mesoscopic energy,mesoscopic damage level and mesoscopic crack number of jointed sandstone under uniaxial compression: the mesoscopic energy evolution process of jointed sandstone is no initial compaction and energy dissipation stage,linear energy storage stage at pre-peak during macroscopic energy evolution is can be subdivided into non-damaged energy storage stage and stable damage energy consumption stage during mesoscopic energy evolution;as the increase of dip angle of joint,the order in which the jointed sandstone reaches the mesoscopic energy characteristic point is medium-dip jointed sandstone(30°,45°,and60°),slow-dip jointed sandstone(0° and 15°),and steep-dip jointed sandstone(75° and90°),the medium-dip joint sandstone has the highest level of mesoscopic accumulated damage at the pre-peak,and the corresponding level of mesoscopic mutation damage has the smallest level at the post-peak;with the increase of length of joint,the easier it is for jointed sandstone to reach the energy characteristic point,the faster the pre-peak crack development process after initiation,the greater the level of mesoscopic accumulated damage at the pre-peak,the slower the corresponding failure process at the post-peak;the final failure morphology of jointed sandstone under mesoscopic simulation is consistent with the results of laboratory uniaxial compression tests.(4)Numerical simulation results of particle flow of jointed sandstone under biaxial compression reveal that: at the same confining pressure gradient: as the increase of dip angle of joint,the rate of accumulation of mesoscopic elastic strain energy of jointed sandstone is firstly decreased and then increased at the peak point,the reduction rate of the mesoscopic energy mutation amplitude is firstly increased and then decreased at the post-peak;when the length of joint exceeds a certain value,the rate of accumulation of mesoscopic elastic strain energy of jointed sandstone decreases with increasing joint length at the peak point;the reduction rate of the mesoscopic energy mutation amplitude decreases with increasing joint length at the post-peak;at the same confining pressure level: high confining pressure conditions will accelerate the cumulative damage of jointed sandstone at the pre-peak,and suppress the mutation amplitude of the mesoscopic energy and damage at the post-peak;mesoscopic mutation damage level determines the final cracking degree of each dip angle of joint of jointed sandstone at the post-peak,and mesoscopic cumulative damage level determines the final cracking degree of each length of joint of jointed sandstone at the pre-peak.(5)The macroscopic and mesoscopic accumulation process of jointed sandstone obtained by experiments and numerical simulations can be represented by an energy selfinhibition evolution model at the pre-peak;from the evolution of the model parameters under different joint forms: considering the mechanism of inhibiting energy conversion under the effect of self-inhibition plays a decisive role in the final result of energy accumulation at the pre-peak;high confining pressure conditions weaken the selfinhibition effect of mesoscopic energy accumulation jointed sandstone at the pre-peak;the self-inhibition of macroscopic and mesoscopic energy of jointed sandstone firstly strengthened and then weakened with the increase of joint dip angle,and gradually strengthened with the increase of joint length at the pre-peak.