Laboratory Test And Failure Law Analysis Of PFC Simulated Jointed Rock

After long-term geological and tectonic movements,defects such as faults,joints,pores,and fissures are usually formed inside the rock mass,and the existence of these defects makes the rock structure exhibit significant inhomogeneity,discontinuity,and anisotropy.Therefore,this paper takes the jointed rock body of the Dali section of the Yunnan Central Diversion Project’s Xiangxuoshan Tunnel as the research object and uses a combination of indoor tests and numerical simulations to research the mechanical behavior and damage mechanism analysis of single-jointed,parallel double-jointed,crossed double-jointed and multi-jointed rocks under the action of uniaxial compression,which is of great guidance for the evaluation of rock engineering stability.The main research work is as follows:(1)Indoor tests on intact rocks and multi-nodular rocks are carried out to provide parametric support for numerical simulation studies.The uniaxial compressive strength of jointed rocks tends to decrease and then increase as the dip angle of the joint group increases,and the compressive strength is from high to low: dry state > natural state >saturated state;the tensile strength of jointed rocks decreases as the dip angle of the joint group increases,and the tensile strength is from high to low: dry state > natural state > saturated state,mainly because the water content of the rocks reduces the intergranular interaction,which makes the rock samples in the progressive The external load does not allow the water present in the fractures and pores of the rock to be discharged in time,resulting in pore water pressure,in addition to generating tensile stresses at the fracture tips,further reducing the strength of the rock and thus accelerating the rock fracture process.(2)The particle flow software PFC2D(Particle Flow Code in 2 Dimensions)was used to establish a numerical model,and the influence of the acceptable parameters of the parallel cohesive model on the macroscopic mechanical behavior was analyzed using the control variables method,and the acceptable parameters were calibrated based on the indoor test results.Most of the fine-scale parameters influence the macro-mechanical parameters of the uniaxial compression simulation tests.In contrast,the parameters of the linear group(linear group effective modulus,linear group stiffness ratio,and friction coefficient)do not influence the direct tensile simulation tests.The fine-scale parameters that affect the damage mode and microcrack development process are consistent,mainly the parallel bonding effective modulus,similar bonding stiffness ratio,friction coefficient,radius multiplier,friction angle,normal bond strength,and tangential bond strength,while the other parameters are less influential.(3)Uniaxial compression simulations were carried out using PFC2 D on intact and single-jointed rocks.The peak stress tends to decrease and then increase as the joint dip angle increases,with the lowest peak stress at 60°;the peak stress gradually decreases as the joint length increases;the compressive modulus of elasticity is positively correlated with the joint dip angle and negatively correlated with the joint length,with the longer the joint length,the more sensitive the joint dip angle is to the compressive modulus of elasticity;the specimens are mostly shear damaged.The microcracks mainly start from the middle and tip of the joints and expand towards the ends and sides of the specimen,forming through cracks;as the inclination of the joints increases,the starting position gradually shifts from the middle of the joints to the tip of the joints,and the starting direction gradually shifts from perpendicular to the tendency of the joints to parallel to the tendency of the joints,the number of cracks first decreases and then increases,and the starting strain first decreases and then increases.As the length of the joints increases,the number of cracks formed by the damage gradually decreases,the distribution area of microcracks decreases,and the microcracks start to crack earlier.(4)Uniaxial compression simulations were carried out using PFC2 D on parallel double-jointed and crossed double-jointed rocks,with the peak stress decreasing and then increasing with increasing crossover angle for L-type crossover,and decreasing with increasing crossover angle for T-type and X-type crossover.The sensitivity of the change in crossover angle to the modulus of elasticity is higher when the crossover angle is L-shaped;the specimens are shear damaged.The number of microcracks decreases as the crossover angle increases,and the simpler the crack,the lower the degree of damage;the number of longitudinal cracks gradually decreases during the process of crossover mode from L-type,T-type to X-type;the initiation point is generally at the node of the joint,and the initiation direction is generally parallel or perpendicular to the joint direction,and the crack develops to the midline position and then turns to the loading direction to continue to expand.(5)Uniaxial compression simulations were carried out on multi-nodular rocks using PFC2 D.The peak stress and compression modulus were relatively close to each other on the numerical simulation and indoor test,while the error between the peak strain was larger;the multijointed rocks showed shear damage at small dips and dislocation and damage along the joints at large dips,with the damage starting near the joints,developing towards the ends and linking the adjacent joints.