Research On Crack Extension Mechanism And Mechanical Property Of Non-straight Fissure

The propagation mechanism and failure characteristics of fractured rock mass have always been the frontiers in the area of rock mechanics.It is well known that because of the unstoppable movement and development of the earth crust,the medium of rock mass presents significant discontinuity,featuring by discontinuous interfaces at different scales,such as fissure,joint,bedding and weak surface.The existence of fissures changes the mechanical properties of the rock mass,reduces the strength of the rock mass,and causes the apparent anisotropy of the rock mass.Due to the influence of geological origin and heterogeneity of local stress,there are not only straight cracks in the rock mass but also some non-straight cracks with certain roughness,whose influence on the fracture mechanics characteristics of the rock mass is also significant.At present,some international and domestic academics have made a lot of research and summary on the cracking problem of a straight fissure.However,there is still no systematic analysis and research on the deformation characteristics,stability and failure mechanism of the rock mass.Therefore,it has wide practical significance for underground rock engineering?mining engineering,uuclear waste storage,etc.?to carry out the research on non-straight cracks and to understand its fracture mode and mechanical properties.In this study,the propagation model and mechanical properties of non-straight crack under uniaxial compression are studied.Through the laboratory experiment,theoretical analysis,numerical simulation and 3D printing technology,the strength and crack coalescence mechanism of brittle rock in uniaxial compression,which with Z-shaped fissure,sine-shaped fissure and double sine-shaped fissures,are analyzed.Based on the subject of the fracture mechanism of non-straight fractures and its application,the main work were carried out in the following aspects:In this paper,the propagation mode and mechanical properties of non-straight fissure under uniaxial compression were mainly studied.Based on the 3D printing technology,in combination with fracture mechanics,the comprehensive application of theoretical and experimental study and numerical simulation,this paper analyzed failure characteristics and macro penetrating mode of the Z-shaped fissure,S-shaped fissure and intermittent double-S fissure in brittle rock mass,to further enhance the understanding of the failure mechanism of fractured rock mass.In this paper,the work in the following aspects has been carried out on the subject of fracture mechanism and mechanical properties of non-straight fissure:?1?The non-straight fissure specimens with homogeneity,no residual stress,and brittleness were prepared by digital engraving and 3D printed technology.Unlike traditional crack processing methods,3D printing technology can produce specimens of complex cracks quickly and repeatedly,and the transparency of the specimen enables good visualization effect.These properties make it possible to obtain a relatively uniform and regular conclusion of the failure mode of the specimen.?2?A uniaxial compression test was carried out on the prefabricated oblique straight fissure and S fissure in natural marble by using a rock mechanics servo-controlled machine.The comparison of propagation and penetration patterns was made between the wing crack of the oblique straight and S fissure.The effect of filling materials were investigated by comparing the propagation modes of non-straight fissure between two kinds of filling materials.?3?The dislocated double-S fissure in natural marble was experimentally studied.The specimens of different geometry distributions were prepared by the automatic engraving machine.The influences of bridge angle,fissure length and inclination angle on crack propagation and failure characteristics were investigated under the uniaxial loading.The failure modes of seven different types were firstly proposed for the dislocated double-S fissure.The RFPA^2D software was used for numerical simulation,which suggested consistent results with the experiments,providing a reference for analyzing the influence of intermittent S fissure on the design of rock engineering.?4?Using 3D printing technology to prepare the specimen of Z-shaped fissure,in combination with the photoelastic experimental method,the distribution and characteristics of stress field around the kinked fracture under uniaxial compression load was quantitatively visualized.The influence of inclination of branch fissure on the propagation and failure mode was investigated by changing the inclination angle of the branch fissure of the Z-shaped fissure.The stress field distribution of kinked fracture under uniaxial compression was obtained and analyzed by using extended finite element method,whose result is in good agreement with the experimental ones.?5?The typical non-straight fissure?single S-shaped fissure?was investigated as the research object,through the experimental and numerical methods with 3D printing of photosensitive resin material.For the influence of inclination angle and curvature of the fissure on the cracking mode,which were concluded as the tip and non-tip cracking,and an empirical model were proposed to predict the cracking mode by the control parameters.