Study On The Influence Of Different Unloading-confining Pressure Rates On Marble Fracture Process

With the development of rock mechanics and the increasing demands of underground engineering,the researches of the rock in the process of excavation unloading is still a hotspot of current rock mechanics research.Taking the marbles of Zhu Madian in Henan as experimental material,this paper performs different loading and unloading indoor tests of the marbles.Based on the above tests,by the numerical simulation software PFC^3D,the paper analyses the marble failure mechanism under the two kinds of stress paths from the perspective of energy and acoustic emission data analysis.The main research contents of this paper are as follows:?1?Analyze the release and transformation of energy in the process of rock failure through the marble conventional triaxial test and constant axial pressure unloading confining pressure test with energy analysis method.The results show that the unloading rate has little effect on the total energy absorbed by rock failure,but affecting on the transformation of energy at each stage of the failure process.The greater unloading rate gets,the slower dissipation energy grow.?2?Analyze the failure process of marble under constant axial pressure unloading path based on the acoustic emission data.It comes to a conclusion:The higher the unloading rate gets,the faster the internal crack develops,and the growth of ring-down count from the unloading point to the failure point becomes larger.The greater unloading rate gets,the severer fracture develops,the more acoustic emission events become.?3?The sensitivity analysis is introduced to the relationship between macro and micro parameters,and the interaction of the microscopic parameters is analyzed.When the meso-parameter is adjusted,the friction coefficient should be determined as much as possible.The elastic modulus is mainly determined by the elastic modulus of the parallel bond.The Poisson's ratio is mainly determined by the parallel bond stiffness ratio,the parallel bond elastic modulus and the particle contact modulus.The peak stress mainly regulates the normal and tangential strength of parallel bonding.?4?Write the PFC^3D program for simulating constant axial pressure unloading confining pressure test.With PFC^3D simulating tests,it is obtained as follows:the stress-strain curve under the two stress paths,the curves of shear displacement diagram,energy and acoustic emission simulation data.Meanwhile,the paper adoptes the contrast analysis through the experiment and simulation.