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Results
Numerical Experiment Model For Heterogeneity Rock Specimens
Wang, S.H. (CRISR, School of Resource and Civil Engineering, Northeastern University) | Tang, C.A. (CRISR, School of Resource and Civil Engineering, Northeastern University) | Xu, T. (CRISR, School of Resource and Civil Engineering, Northeastern University) | Hudson, J.A. (Imperial College and Rock Engineering Consultants, 7 The Quadrangle)
ABSTRACT A numerical parameter-sensitivity analysis has been conducted to evaluate the effect of heterogeneity on the fracture processes and strength characterization of rock under uniaxial compression loadings. The deformation mechanisms of rock under different constant confining pressures was briefly analyzed based on Continuum damage mechanics and the effect of confining pressure on deformation, strength and macroscopic fracture patterns of model rock specimens are also studied using Rock Failure Process Analysis (RFPA) code, that show the nucleation and growth of macrocracks in relatively heterogeneous specimens under uniaxial loading. In this simulator, the heterogeneity of rock is considered by assuming that the material properties of elements conform to Weibull distribution, an elastic damage-based law that considered the strain-rate dependency is used to describe the constitutive law at mesoscopic scale, and finite element program is employed as a basic stress analysis tool. The theoretical analysis and numerically obtained results duplicate the deformation, strength (such as Young's modulus, compressive strength, etc) and macroscopic fracture patterns observed in laboratory. While the details of macrocrack formation varied from specimen to specimen, a number of features were consistently obtained in the numerical simulations. The theoretical studies and numerical simulations are extremely instructive and indicative for investigating some catastrophic hazard phenomena such as rock bursts, instability induced by excavation. Splitting and faulting failure modes often observed in experiments are also observed in the simulations under uniaxial compression. It is found that tension fractures are the dominant failure mechanism in both splitting and faulting processes. The numerical simulation shows that faulting is mainly a process of tensile fractures, often en echelon fractures, developed in a highly stressed shear band, just is as observed in actual Uniaxial compression tests. In these simulations, the same diffused AE events or micro fractures but with higher count number also appeared in the early stage of loading. INTRODUCTION The uniaxial compressive strength of a rock is one of the simplest measures of strength. It may be regarded as the largest stress that a rock specimen can carry when a unidirectional stress is applied to the ends of a specimen. In other words, the unconfined compressive strength represents the maximum load supported by the specimen during the test divided by the cross sectional area of the specimen. Although the utility of the compressive strength value is limited, the unconfined compressive strength allows comparisons to be made between rocks and provides some indications of rack behavior under more complex stress systems. Experimentally, researchers have undertaken the task of loading specimens to obtain better knowledge of the compressive failure mechanisms and considerable discussion has been devoted in the literature to this test method (Pells,1993; Wawersik etc,1970; Wawersik & Brace,1971; Lockner DA, et al.,1992; Lockner & Byerlee,1991; Cox & Meredith,1993; Blair & Cook,1998;etc.). Though this mode of failure has been studied in detail for decades, the details of the failure mechanisms, including the microfracture initiation, propagation, coalescence, axial splitting, shearing, etc., are not fully understood and still remain the subject of considerable scientific interest.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics (0.46)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Faults and fracture characterization (0.89)
Progressive Failure And Mechanical Behavior of Transversely Isotropic Rocks
Liang, Z.Z. (CRISR, Northeastern University) | Wang, S.H. (CRISR, Northeastern University) | Tang, C.A. (CRISR, Northeastern University) | Zhang, J.X. (CRISR, Northeastern University) | Xu, T. (Dalian University) | Song, L. (Dalian University)
ABSTRACT Based on mesoscopic damage mechanics, numerical codes RFPA is developed to simulate the Complete failure process of seven transversely isotropic rock samples subjected to uniaxial loading. The rock samples are composed of two different rock materials and they are formed with different dip angles between the rock layer orientation and the loading direction. Complete stress-strain curves are obtained and the deformability and failure behaviors are described. Numerical results show rock layer dip angle of transversely isotropic rocks has significant influence on the fracture during the progressive failure process, such as peak strength, failure manners, and deformational behavior et al. It is suitable to apply different failure criteria according to different failure modes caused by layer dip angle. INTRODUCTION Many types of rocks such as sedimentary rocks and metamorphic rocks containing fabric with preferentially parallel arrangements of flat or long minerals may be transversely isotropic. Isotropic rocks cut by regular discontinuities may also exhibit obvious trans- Versely isotropic properties, such as granite and basalt (Wittke 1990). In civil and mining engineering, such as In the analysis of stability of slope, underground excavation and boreholes for mining, many failures results from the anisotropy can be found. The mechanics properties of transversely isotropic rocks are the same along any orientations on one plan and different on the perpendicular plan. Significant errors may occur if anisotropic rocks are treated as isotropic rocks. In the last several decades, considerable efforts are made on the study of anisotropic rocks, from both experimental and theoretical points of view (Donath 1964; Borecki et al 1981; Brady & Brown 1993; Hoek 1964' Jaeger 196 0; Duveau & Shao 1998; Cazacu et al 1998). Many scholars have developed failure criteria for the transversely Isotropic rocks to get variation of rock mechanics properties with the orientation angles under various confining pressures. Jaeger (1960) introduced a basic analysis on rocks containing well-defined, parallel discontinuity. He considered that if the rock failure does not occurred along the discontinuity, the rock can be treated as isotropic rocks. Duveau & Shao (1998) provided modification by replacing the Mohr-Coulomb criterion with a non-linear model to express the strength along the discontinuity. The strength criteria for the transversely isotropic rocks developed by McLamore & Gray (1967), Hoek & Brown (1964) and Ramarnurthy (1993) generally provide fairly accurate simulation of the experimental data. A more general criterion was proposed by Hill (1950) based on Mises's isotropic criterion. Pariseau (1972) and Cazacu (1998) et al. extended Hill's criterion to account for the effect of the hydrostatic stresses. As pointed out by Tian (2001), both of their criteria describe the continuous variation of strength with the orientation angle, which is referred to herein as the continuous model and the continuous model is not suitable for the shoulder and undulatory type of rocks. Though a lot of constitutive laws and failure criteria have been proposed based on experimental results, the parameters used in the theoretical models, have considerable dependence on the experimental results.
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)