The Study On Experiment And Numerical Simulation Of Fracture Progress Of3D Flaws In Brittle Materials

The initiation, growth, coalescence and destruction rules through evolution is the basis of the research on damage and instability of rock mass, the influence of seepage to rock mass strength is also attached great importance by the engineering field. Previous studies tend to simplify the three-dimensional problem to the two-dimensional, due to the complexity. However this simplification is often not fully reflect the expansion of the law of three-dimensional fracture damage. In recent years, three-dimensional extension fracture morphology and failure mechanisms become an important topic in the field of fractured rock mass, process and mechanism of three-dimensional fracture fractured rock mass under stress conditions still further. In addition, instability of some rock engineering often closely related with groundwater. Therefore, to carry out the study of the failure rule of changes and new characteristics of the fractured rock mass under water pressure condition is also very important. In this article, through the experimental research, theoretical analysis and numerical simulation method, research the crack propagation law and mechanism of the rock-like specimens; Using microscopic theory, reveal the expansion process and failure modes of cracks, analyses the failure process and the rule of the strength the crack specimen under hydraulic conditions, and the analysis method is used in engineering practice. This paper completed and carried out the following aspects of work:1) Developed a model specimen made of a kind of resin which ratio of tensile and compressive strength is1/6.6in low. This kind of material is brittle and accord with the basic characteristics of the rock, the mechanical parameters of this matter are close to the Marble’s and which could largely simulate these rocks. Moreover, people can easily understand crack propagation law through intuitively observing the crack propagation on the basic of its transparency. The authors used the material making specimens containing hollow fractures, and compressed them under water pressure conditions. Compression and hydrofracturing test can be carried out under different water pressure conditions and lateral pressure using this hollow pre-fractured specimen.2) Study the new crack initiation, propagation, and coalescence law of pre-fractured specimen by uniaxial compression tests of transparent specimen. Studies have shown that three-dimensional specimens under compression fracture process have gone through four phases. This four deformation stages are fully correspond with rock specimens, and as the expansion characteristics. Wrap-like wing cracks and petal-shaped cracks which was speculated by previous were shown during the experiment.Unsaturated resin material specimen is homogeneous material specimen, with on no shortage except the pre-fracture, therefore, there is no other defects interference in the process of destruction. Comparison with heterogeneous material testing, homogeneous materials specimen has the same expansion mode during the new crack initiation and propagation stages. However, as affected by heterogeneity defects, the homogeneous materials specimen is different with heterogeneous material specimen in the final form of destruction.3) Cracking specimen compression experiment has been conducted under hydraulic pressure. Based on the experimental result, the destruction processes and phenomena of cracking specimens, under hydraulic pressure or without it, have shown similarities and differences. Specimens, under hydraulic pressure and without hydraulic pressure, show warping wing-like cracks at the head of the long axis of the elliptic crack, whereas there are no petal-like cracks for specimens under hydraulic pressure. Under hydraulic pressure, the threshold pressure of forming new cracks and specimens totally damage is smaller, which means the sustainable pressure of the specimens under hydraulic pressure has decreased. At the same time, the higher hydraulic pressure, the smaller axial pressure of forming new cracks and specimens damage.4) Elastic-brittle damage model is adopted to simulate the single and double cracks under uniaxial loading and destruction process by secondary development function of FLAC3D, and find that the result of calculation is very close to test results. By calculating the process of simple failure under different working condition of lateral pressure, as the increasing process of confining pressure, the initiation-stress, extension point and peak-strength was also increased, and the extending forms of crack was different.5) The paper investigated the rules of crack initiation and extending under different hydraulic pressure by the method of fluid-solid interaction. The increasing of hydraulic pressure reduced the initiation-stress and peak-strength of crack. Results of numerical simulation show that the final failure flaw keeps perpendicular with minimum principal stresses; the failure mode towards to horizontal direction while the vertical principal stress less than the horizontal principal stress, and it towards to vertical direction while the vertical principal stress more than the horizontal principal stress.6) Take an example of large underground excavation and carrying on the excavation numerical simulation based on a quasi-three dimensional model. The results basically reflect the variation of rock stress field and displacement field during the excavation process. Especially adopt the mesoscopic model method during the process. Results basically reflect the extending rules of original flaws around chambers and influence by seepage during excavation.