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1.
岩石断裂韧度表征其抵抗裂纹起裂和扩展的能力,作为其力学性能的一个重要指标,在岩石力学理论研究与岩体工程应用中有着不可替代的作用。由于岩石结构的复杂性,其破坏形式大多呈现为复合型断裂破坏,研究复合型加载条件下岩石断裂韧度具有重要的意义。为了研究锈岩的断裂力学性能,以便其在建筑工业中得到更为广泛的应用,通过18个中心裂纹圆盘（CSTBD）试件径向受压试验,进行了复合型加载条件下锈岩断裂韧度的试验研究。测得了锈岩在纯I型,纯II型以及复合型加载时的断裂韧度,并将试验结果与基于广义最大周向应力（GMTS）准则的理论值进行了对比分析,结果表明：锈岩的纯I型断裂韧度为1.01 MPa?m0.5,而纯II型断裂韧度为1.51 MPa?m0.5,是纯I型断裂韧度的1.49倍,这与基于GMTS准则的理论值1.34非常接近,而比基于最大周向应力（MTS）准则的理论值0.87大很多。裂纹尖端附近的T应力及断裂过程区裂纹尖端的临界距离rc对岩石类材料的开裂路径以及复合型断裂韧度都有较大的影响。考虑了T应力的广义最大周向应力（GMTS）准则能很好的预测试验结果。 相似文献
2.
Previous studies are mainly concentrated on the use of the semi-circular bend (SCB) specimen for determining the entire mixed-mode I-II fracture toughness of rock, while less attention has been paid to its mixed-mode fracture process. In this situation, this study investigated mixed-mode fracture behavior of the SCB specimen using the extended finite element method (X-FEM). The crack growth trajectory, crack initiation angle and onset of fracture were discussed in detail. This paper is expected to provide a better understanding of mixed-mode fracture process of the SCB specimen occurring during fracture initiation and propagation. 相似文献
3.
Yao Yao 《Rock Mechanics and Rock Engineering》2012,45(3):375-387
Hydraulic fracturing technology is being widely used within the oil and gas industry for both waste injection and unconventional
gas production wells. It is essential to predict the behavior of hydraulic fractures accurately based on understanding the
fundamental mechanism(s). The prevailing approach for hydraulic fracture modeling continues to rely on computational methods
based on Linear Elastic Fracture Mechanics (LEFM). Generally, these methods give reasonable predictions for hard rock hydraulic
fracture processes, but still have inherent limitations, especially when fluid injection is performed in soft rock/sand or
other non-conventional formations. These methods typically give very conservative predictions on fracture geometry and inaccurate
estimation of required fracture pressure. One of the reasons the LEFM-based methods fail to give accurate predictions for
these materials is that the fracture process zone ahead of the crack tip and softening effect should not be neglected in ductile
rock fracture analysis. A 3D pore pressure cohesive zone model has been developed and applied to predict hydraulic fracturing
under fluid injection. The cohesive zone method is a numerical tool developed to model crack initiation and growth in quasi-brittle
materials considering the material softening effect. The pore pressure cohesive zone model has been applied to investigate
the hydraulic fracture with different rock properties. The hydraulic fracture predictions of a three-layer water injection
case have been compared using the pore pressure cohesive zone model with revised parameters, LEFM-based pseudo 3D model, a
Perkins-Kern–Nordgren (PKN) model, and an analytical solution. Based on the size of the fracture process zone and its effect
on crack extension in ductile rock, the fundamental mechanical difference of LEFM and cohesive fracture mechanics-based methods
is discussed. An effective fracture toughness method has been proposed to consider the fracture process zone effect on the
ductile rock fracture. 相似文献
4.
In this paper, firstly the mesoscopic elemental mechanical model for elastic damage is developed and implemented into the rock and tool interaction code (R-T2D). Then the failure processes of a heterogeneous rock specimen subjected to a wide variety of confining pressures (0–80 MPa) are numerically investigated using the R-T2D code. According to the simulated results, on the one hand, the numerical simulation reproduced some of the well-known phenomena observed by previous researchers in triaxial tests. Under uniaxial compression, rock failure is caused by a combination of axial splitting and shearing. Dilatancy and a post-failure stage with a descending load bearing capacity are the prominent characteristics of the failure. As the confining pressure increases, the extension of the failed sites is suppressed, but the individual failure sites become dense and link with each other to form a shear fracture plane. Correspondingly, the peak strength, the residual strength and the shear fracture plane angle increase, but the brittleness decreases. When the confining pressure is high enough, the specimen behaves in a plastic manner and a narrow shear fracture plane leads to its failure. The prominent characteristics are volume condensation, ductile cataclastic failure, and a constant load bearing capacity with increasing strain. On the other hand, the numerical simulation revealed some new phenomena. The highest microseismicity events occur in the post-failure stage instead of the maximal stress, and most of the microseismicity energies are released in the failure localization process. As the confining pressure increases, the microseismicity events in the non-linear deformation stage increase dramatically and the ratio between the energies dissipated at the non-linear deformation stage and those dissipated in the whole loading process increases correspondingly. Therefore, it is concluded that the developed mesoscopic elemental mechanical model for elastic damage is able to reproduce accurately the failure characteristics in loading rock specimens under triaxial conditions, and the numerical modelling can furthermore obtain some new clarifications of the rock fracture process. 相似文献
5.
为了揭示水压致裂法和巴西劈裂法测量岩石抗拉强度的关系,开展了理论和现场试验研究。基于经典的水压致裂法理论,推导了不同围压下钻孔破裂压力和抗拉强度。利用断裂力学理论建立了水压致裂法和巴西劈裂法测得抗拉强度的关系。利用预制切槽方法模拟天然裂纹,对水力裂缝的起裂压力进行了研究。结果表明：围压为最大主应力等于3倍最小主应力测得的抗拉强度大于围压为0测得的抗拉强度;水压致裂法和巴西劈裂法测量抗拉强度关系与应力场、裂纹长度、断裂韧度3个变量有关;通过在晋城矿区王台铺矿的预制切槽试验,运用断裂力学建立的抗拉强度计算式更为符合现场实际。研究结果可为坚硬难垮落顶板预制切槽的水力压裂设计提供参考。 相似文献
6.
This paper presents a numerical study on the desiccation cracking process of clayey soil. The initiation and propagation of cracks were investigated using finite element code, including the damage-elastic cohesive fracture law to describe the behaviour of cracks. The coupling between the hydraulic behaviour (moisture transfer in the soil matrix and in the cracks) and the mechanical behaviour (volume change of the soil matrix and development of cracks) were also considered. The results of a laboratory experiment performed on clay soil, taken from a literature review, were used to evaluate the numerical modelling. The results show that the code can reproduce the main trends observed in the experiment (e.g., shrinkage related to drying, crack development). In addition, the numerical simulation enables the identification of other phenomena, such as the evolution of suction and stress related to drying and the development of a single crack. These phenomena are difficult to observe experimentally. 相似文献
7.
危岩是三峡库区典型的地质灾害类型之一,而主控结构面受荷断裂扩展是危岩发育成灾的关键核心。将危岩主控结构面类比为宏观裂纹,利用扩展有限元法在模拟裂纹扩展方面的优势,基于考虑裂纹面水压力作用的虚功原理推导出了采用扩展有限元法分析水力劈裂问题的控制方程,给出了危岩主控结构面水力劈裂问题的扩展有限元实现方法,对重庆万州太白岩危岩主控结构面的水力劈裂进行了数值模拟分析。计算结果表明：暴雨是威胁危岩稳定性的最敏感因素,随着裂隙水压力上升,裂端拉应力会急剧升高,危岩的稳定性降低;I型裂纹扩展是危岩主要的结构面扩展形式,结构面一旦发生开裂,将处于非稳定扩展状态。 相似文献
8.
9.
Modeling the Effects of Heterogeneity and Anisotropy on the Excavation Damaged/Disturbed Zone (EDZ) 总被引：2，自引：0，他引：2
S. H. Wang C. I. Lee P. G. Ranjith C. A. Tang 《Rock Mechanics and Rock Engineering》2009,42(2):229-258
Summary When modeling the mechanical behavior of underground excavations, it is necessary to include the influence of the rock mass
characteristics on the Excavation Damaged/Disturbed Zone (EDZ). In this paper, the Realistic Failure Process Analysis code,
RFPA, is used to model the extent of the EDZ. The inhomogeneous characteristics of rock at the mesoscopic level are included
by assuming that the material properties of the constituent elements conform to a Weibull distribution; the anisotropy is
incorporated as a transversely isotropic medium; the non-elastic characteristic is simulated via an elastic damage-based constitutive
law. A finite element program is adopted as the basic stress analysis tool. In this study, a notable feature is that no a
priori assumptions need to be made about where and how fracture and failure will occur – cracking can take place spontaneously
and can exhibit a variety of mechanisms when certain local stress conditions are met. The deformation and failure process
of anisotropic rock around excavations of different geometries is analyzed, and compared to experimental tests, showing similar
fracture patterns. Additionally, the effect of confining stress and of different material layers is modeled and discussed.
It is found that the model clearly illustrates that fracturing, both initiation and propagation, occurs as a combination of
the stress concentrations and weakness planes introduced via the transverse anisotropy – which could represent either foliations
or ubiquitous joint sets.
Correspondence: Dr. Shuhong Wang, Box 265, School of Resource and Civil Engineering, Northeastern University, Shenyang 110004,
P.R. China 相似文献
10.
运用数值流形法在非连续介质领域的独特优势,并结合断裂力学的基本原理,分析了重力坝的水力劈裂破坏问题,实现了重力坝起裂、扩展和渐进破坏的全过程。充分发挥应力强度因子判别法和带抗拉强度的摩尔-库仑破坏准则各自的优势,根据不同情况选取其中某种方法确定断裂和扩展方向,且不需要预制初始裂纹。选取一个算例两种工况分析了重力坝在不考虑裂纹面内水压力和考虑裂纹面内水压力的水力劈裂破坏情况。计算结果表明,在重力坝的水力劈裂中,当不考虑裂纹面内水压力时,坝踵处裂纹向下游和深部扩展,上游折坡点处裂纹属于压剪型破坏;当考虑裂纹面内水压力时,坝踵处裂纹偏向深度方向扩展,折坡点处的裂纹逐渐由压剪破坏变成了拉剪破坏,并且考虑裂纹面内水压力后坝体破坏所需要的时步减少,故而考虑裂纹面内水后降低了重力坝的安全系数。该方法加深了对重力坝水力劈裂破坏的认识,具有较大的实际应用价值。 相似文献
11.
The stress-strain behaviour of rock material related to fracture under compression 总被引：12，自引：0，他引：12
Fracture is the main reason for the non-linear behaviour of hard rocks. The fracture mechanics of rock is studied in this article by analysis of the fracture process under compression. A constitutive model that describes the relationship between the macro deformation of rock and the micro fracture within rock is developed. The propagation of microcracks, the non-linearity of deformation, the loading-and-unloading hysteresis and the variation of the apparent Young's modulus and Poisson's ratio are studied using the developed model. The model simulations demonstrate that: (1) the fracture toughness, initial crack length, crack density, and Young's modulus are four crucially important parameters that affect the deformation behaviour of rock; (2) the elastic parameters (E and v) of the rock matrix should be measured in triaxial tests. If they are measured in uniaxial tests, the upper straight unloading portion of the stress-strain curve is suggested to be used for the purpose, unless the closure effect of open cracks will be included in the estimations. In addition (3), the slope of the reloading stress-strain curve is a measure of the damage in material. 相似文献
12.
The process of cutting homogeneous soft material has been investigated extensively. However, there are not so many studies on cutting heterogeneous brittle material. In this paper, R‐T2D (Rock and Tool interaction), based on the rock failure process analysis model, is developed to simulate the fracture process in cutting heterogeneous brittle material. The simulated results reproduce the process involved in the fragmentation of rock or rock‐like material under mechanical tools: the build‐up of the stress field, the formation of the crushed zone, surface chipping, and the formation of the crater and subsurface cracks. Due to the inclusion of heterogeneity in the model, some new features in cutting brittle material are revealed. Firstly, macroscopic cracks sprout at the two edges of the cutter in a tensile mode. Then with the tensile cracks releasing the confining pressure, the rock in the initially high confining pressure zone is compressed into failure and the crushed zone gradually comes into being. The cracked zone near the crushed zone is always available, which makes the boundary of the crushed zone vague. Some cracks propagate to form chipping cracks and some dip into the rock to form subsurface cracks. The chipping cracks are mainly driven to propagate in a tensile mode or a mixed tensile and shear mode, following curvilinear paths, and finally intersect with the free surface to form chips. According to the simulated results, some qualitative and quantitative analyses are performed. It is found that the back rake angle of the cutter has an important effect on the cutting efficiency. Although the quantitative analysis needs more research work, it is not difficult to see the promise that the numerical method holds. It can be utilized to improve our understanding of tool–rock interaction and rock failure mechanisms under the action of mechanical tools, which, in turn, will be useful in assisting the design of fragmentation equipment and fragmentation operations. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
13.
层理弱面对层状岩石的力学特性影响较显著，为了研究层理面特性对岩石断裂力学特性的影响，开展了具有不同层理方向的砂岩试样三点弯试验，探讨了砂岩断裂韧度及断裂模式的各向异性。之后基于有限元中的黏聚单元建立了数值模型，采用数值模拟方法研究了层理面强度对各层理角度试样断裂力学行为的影响规律。结果表明：层理方向影响下砂岩的断裂韧度及模式存在各向异性；同一层理方向试样的断裂韧度随层理面强度的增大而增大，且试样的层理面与加载方向夹角越小，断裂韧度受层理面强度变化影响越明显；试样的断裂模式不仅与层理面强度有关，还受层理倾角的控制，层理面与加载方向夹角θ = 0o试样断裂模式基本不受层理面强度影响，θ = 30o试样主要沿层理面张拉或剪切破坏，且沿层理面的破裂长度随层理面强度的降低逐渐增大；层理面强度较大时，θ = 45o试样主要沿层理面张拉破坏，θ = 60o～90o试样主要以贯穿层理的张拉破坏为主；层理面强度较小时，θ = 45o～90o试样均以沿层理面的剪切破坏为主，其中θ = 45o试样沿层理剪切长度最大。另外，通过数值模拟结果分析了层理面强度及方向对试样的起裂角及裂纹扩展路径产生的影响。该研究成果可作为层状岩石断裂力学理论的有益补充。 相似文献
14.
在试验室进行裂纹稳定扩展及非稳定扩展的研究,其试验基座以楔形劈裂试验为基础改良而成,考虑材料的均质性,试验试体采用供铺设地板或建筑用外墙之天然石材。试验过程中利用裂缝应变片即时记录系统求出试体在稳定扩展及非稳定扩展下的裂纹扩展速度及其分形特性。结果表明,稳定扩展速度范围约在0.113～313.043 cm/s;非稳定扩展速度范围约在0.094～2 489.816 cm/s;亚临界分形维数范围约在0.994 3～1.036 6;起裂断裂韧性范围约在1.891 5～3.500 1 MPa?m1/2;分形亞臨界斷裂韌性范围约在2.063 6～3.712 8 MPa?m1/2。 相似文献
15.
Buoyancy-driven propagation of an isolated fluid-filled crack in rock: implication for fluid transport in metamorphism 总被引：1，自引：0，他引：1
Yoshito Nakashima 《Contributions to Mineralogy and Petrology》1993,114(3):289-295
A new model for upward transport of buoyant fluid released during metamorphism is proposed. The model is fluid transport by buoyancy-driven propagation of isolated fluid-filled cracks. The mechanical behavior of a two-dimensional, isolated, vertical, and fluid-filled crack in impermeable rock is investigated using linear fractire mechanics and fluid dynamics. The results show that steady-state crack propagation which causes long-distance transport of the fluid occurs when the vertical cross-sectional area of the crack exceeds a critical value. Propagation velocity and average thickness of the crack under the steady-state propagation regime are expressed explicitly by the following seven parameters: vertical crack length; rigidity, Poisson's ratio, and fracture toughness of the rock; fluid viscosity; density difference between the rock and the fluid; gravitational acceleration. An isolated H2O-filled crack of vertical length 100 m, for example, propagates upwards in the crust at 0.3 m/s with the average thickness 0.2 mm when the following likely values are assumed: 0.1 mPa s for the H2O viscosity; 3 MPa m1/2 for the fracture toughness of the crustal rock. The application of the obtained results to the transport of H2O released during metamorphism suggests that the number density of isolated cracks propagating in the crust is very low. Since the propagation velocity is high, our model is suitable particularly for fluid transport through hot quartz-rich rock where fluid-filled cracks have geologically short lifetimes. 相似文献
16.
岩体中普遍存在着断层﹑节理和裂隙等结构面,这些结构面的存在和发展对岩体的整体强度﹑变形及稳定性有极大的影响。因此,研究岩体中原生结构面的萌生﹑发展以及贯通演化过程对评估岩体工程安全性和可靠性具有非常重要的理论与现实意义。扩展有限元法（XFEM）作为一种求解不连续问题的有效数值方法,模拟裂隙时独立于网格,因此,在模拟岩体裂隙扩展﹑水力劈裂等方面具有独特优势。针对扩展有限元法的基本理论及其在岩体裂隙扩展模拟中的应用展开了研究,建立了扩展有限元法求解岩体裂隙摩擦接触、岩体裂隙破坏等问题的数值模型,并将计算模型应用于岩质边坡稳定性分析和重力坝坝基断裂破坏等工程问题。 相似文献
17.
Micromechanical Model for Simulating the Fracture Process of Rock 总被引：25，自引：3，他引：25
Summary A micromechanical model is proposed to study the deformation and failure process of rock based on knowledge of heterogeneity of rock at the mesoscopic level. In this numerical model, the heterogeneity of rock at the mesoscopic level is considered by assuming the material properties in rock conform to the Weibull distribution. Elastic damage mechanics is used to describe the constitutive law of meso-level elements, the finite element method is employed as the basic stress analysis tool and the maximum tensile strain criterion as well as the Mohr-Coulomb criterion is utilized as the damage threshold. A simple method, similar to a smeared crack model, is used for tracing the crack propagation process and interaction of multiple cracks. Based on this model, a numerical simulation program named Rock Failure Process Analysis Code (RFPA) is developed. The influence of parameters that include the Weibull distribution parameters, constitutive parameters of meso-level elements and number of elements in the numerical model, are discussed in detail. It is shown that the homogeneity index is the most important factor to simulate material failure with this model. This model is able to capture the complete mechanical responses of rock, which includes the crack patterns associated with different loading stages and loading conditions, localization of deformation, stress redistribution and failure process. The numerical simulation of rock specimens under a variety of static loading conditions is presented, and the results compare well with experimental results. 相似文献
18.
The development of the Brazilian disc test for determining indirect tensile strength and its applications in rock mechanics are reviewed herein. Based on the history of research on the Brazilian test by analytical, experimental, and numerical approaches, three research stages can be identified. Most of the early studies focused on the tensile stress distribution in Brazilian disc specimens, while ignoring the tensile strain distribution. The observation of different crack initiation positions in the Brazilian disc has drawn a lot of research interest from the rock mechanics community. A simple extension strain criterion was put forward by Stacey (Int J Rock Mech Min Sci Geomech Abstr 18(6):469–474, 1981) to account for extension crack initiation and propagation in rocks, although this is not widely used. In the present study, a linear elastic numerical model is constructed to study crack initiation in a 50-mm-diameter Brazilian disc using FLAC3D. The maximum tensile stress and the maximum tensile strain are both found to occur about 5 mm away from the two loading points along the compressed diameter of the disc, instead of at the center of the disc surface. Therefore, the crack initiation point of the Brazilian test for rocks may be located near the loading point when the tensile strain meets the maximum extension strain criterion, but at the surface center when the tensile stress meets the maximum tensile strength criterion. 相似文献
19.
Experimental and Numerical Studies on Determination of Indirect Tensile Strength of Rocks 总被引：4，自引：2，他引：2
Nazife Erarslan Zheng Zhao Liang David John Williams 《Rock Mechanics and Rock Engineering》2012,45(5):739-751
Indirect tension tests using Brisbane tuff Brazilian disc specimens under standard Brazilian jaws and various loading arcs were performed. The standard Brazilian indirect tensile tests caused catastrophic, crushing failure of the disc specimens, rather than the expected tensile splitting failure initiated by a central crack. This led to an investigation of the fracturing of Brazilian disc specimens and the existing indirect tensile Brazilian test using steel loading arcs with different angles. The results showed that the ultimate failure load increased with increasing loading arc angles. With no international standard for determining indirect tensile strength of rocks under diametral load, numerical modelling and analytical solutions were undertaken. Numerical simulations using RFPA2D software were conducted with a heterogeneous material model. The results predicted tensile stress in the discs and visually reproduced the progressive fracture process. It was concluded that standard Brazilian jaws cause catastrophic, crushing failure of the disc specimens instead of producing a central splitting crack. The experimental and numerical results showed that 20° and 30° loading arcs result in diametral splitting fractures starting at the disc centre. Moreover, intrinsic material properties (e.g. fracture toughness) may be used to propose the best loading configuration to determine the indirect tensile strength of rocks. Here, by using numerical outcomes and empirical relationships between fracture toughness and tensile strength, the best loading geometry to obtain the most accurate indirect tensile strength of rocks was the 2α?=?30° loading arc. 相似文献
20.
岩石裂纹的扩展是一个经典的不连续问题,常规有限元方法难以实现裂纹扩展过程的仿真模拟。扩展有限元法(XFEM)实现了计算网格与不连续面相互独立,因此模拟移动的不连续面时无需对网格进行重新剖分。本文介绍了XFEM基本原理和岩石断裂力学常用判据,尝试对岩石类材料单缝Ⅰ型三点弯曲、单缝剪切和双缝平板实验进行模拟。分析结果表明:扩展有限元模拟岩石类材料断裂问题不受网格划分限制,裂纹以实际应力场分布随机扩展;直观地给出岩样的微裂纹产生、演化,直至完全破坏的全过程,并与实验结果吻合。该方法能够应用到岩石断裂力学方面的研究,模拟岩石类材料的宏细观破坏过程,为解决复杂问题提供了方便的途径。 相似文献