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1.
Rock masses encountered in the field are jointed and highly anisotropic. An important manifestation of this characteristic of rock masses is that the blocks, when slipping, separate and create voids in the mass resulting in high lateral strain even under low axial stress. It has been shown in this study that the ratio of lateral to axial strain may be very high, especially, if the joints are critically oriented. The assumption of isotropic linearly elastic material is not applicable in such situations. This observation is based on the outcome of an extensive laboratory testing programme, in which a large number of specimens of a jointed rock mass with various joint configurations were tested under uniaxial loading conditions. The trends of experimental results for both lateral strain ratio and rock mass strength have also been verified through distinct element modelling. The reason for high lateral strains has been attributed to the creation of voids and also to the fact that permanent deformations due to slip commence along rock joints right from the start of loading process. A simple mechanistic model has also been suggested to explain the high values of lateral strain for rough and dilatant rock joints. The lateral strains in such situations are important in the design of rock bolts. An example from a recently completed hydroelectric project has also been discussed where high lateral strain was found to be responsible for excessive wall closure and failure of rock bolts. 相似文献
2.
Microplane damage model for jointed rock masses 总被引：1，自引：0，他引：1
The paper presents a new microplane constitutive model for the inelastic behavior of jointed rock masses that takes into account the mechanical behavior and geometric characteristics of cracks and joints. The basic idea is that the microplane modeling of rock masses under general triaxial loading, including compression, requires the isotropic rock matrix and the joints to be considered as two distinct phases coupled in parallel. A joint continuity factor is defined as a microplane damage variable to represent the stress‐carrying area fraction of the joint phase. Based on the assumption of parallel coupling between the rock joint and the rock matrix, the overall mechanical behavior of the rock is characterized by microplane constitutive laws for the rock matrix and for the rock joints, along with an evolution law for the microplane joint continuity factor. The inelastic response of the rock matrix and the rock joints is controlled on the microplane level by the stress–strain boundaries. Based on the arguments enunciated in developing the new microplane model M7 for concrete, the previously used volumetric–deviatoric splits of the elastic strains and of the tensile boundary are avoided. The boundaries are tensile normal, compressive normal, and shear. The numerical simulations demonstrate satisfactory fits of published triaxial test data on sandstone and on jointed plaster mortar, including quintessential features such as the strain softening and dilatancy under low confining pressure, as well as the brittle–ductile transition under higher confining pressure, and the decrease of jointed rock strength and Young's modulus with an increasing dip angle of the joint. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
3.
C. M. Gerrard 《Computers and Geotechnics》1985,1(4):293-318
The concept of reinforced multi-laminates has been developed and applied to the analysis of reinforced jointed rock masses. The discontinuities and reinforcements in the rock mass are assumed to occur in regular sets, with relatively close spacing within sets. The constitutive equations are established for an ‘equivalent material’, this being identical in its mechanical response to the reinforced jointed rock mass, consisting of its components, i.e. rock material, sets of discontinuities, and sets of reinforcements with associated sets of interfaces. An elasto-visco/plastic algorithm is used so that each component is described by its elastic, failure and flow properties together with its relative orientation. The constitutive equations for the ‘equivalent material’ can be applied to determine optimal reinforcement arrangements for problems of various levels of complexity. Several practical examples illustrating this are contained in a companion paper. 相似文献
4.
Back analysis of an excavated slope failure in highly fractured rock mass: the case study of Kargar slope failure (Iran) 总被引：2，自引：1，他引：1
Mostafa Sharifzadeh Mohsen Sharifi S. Mohammad Delbari 《Environmental Earth Sciences》2010,60(1):183-192
This paper examines the failure of Kargar cut slope located at the south part of Esfahan subway using analytical and numerical
back analysis methods. The excavated trench has 27 m depth with near vertical walls due to the space limitation around it.
The geology of the area comprises weathered and heavily jointed shale and sandstone overlaid by alluvium deposits. Despite
the slope being supported by shotcrete and fully grouted rock bolts, a catastrophic failure occurred at the east wall. Due
to the uncertainty about the causes of failure initiation, back analyses have been performed via both the limit equilibrium
and numerical method for considering various probable mechanisms. In the back analysis with limit equilibrium method, the
rock mass is assumed as an equivalent continuum and Hoek–Brown failure criterion and geological strength index (GSI) are applied
to calculate the shear strength parameters. The results show that GSI value was 33 in the failed mass. In the numerical back
analysis, the distinct element method is applied to study the contribution of rock joints to the failure and progressive rock
mass strength degradation until failure. The results show that threshold values of joint cohesion and friction were 0.2 MPa
and 30°, respectively. Also the modeled slip surface being step-shaped agrees with the observed one. 相似文献
5.
节理岩体几何结构非常复杂,研究其渗流特性对于指导含水岩层稳定性分析具有重要价值。应用离散裂隙网络模型DFN方法,基于VC++6.0软件平台,建立了平面渗流分析方法,分析了节理岩体不同几何分布情况下的渗透率张量特征,通过定义渗流定向性系数对岩体渗流的定向性特征进行了定量分析。结果表明：单组节理岩体渗流具有明显的各向异性特征,渗流定向性随着节理角度变化显著;节理随着节理贯通性增加,节理渗透率呈现对数增加趋势;两组节理情况下,各向异性特征随着节理组间夹角变化;两组节理岩体渗流特征研究中,正交分布下,岩体仍存在各向异性,但渗流定向性系数较低;当节理倾角服从正态分布时,随着节理倾角标准差增大,渗透率增加;两组节理夹角不同时,节理渗透主方向倾角随着夹角增大而相应增大,基本沿两组节理夹角方向的角平分线方向。 相似文献
6.
Analysis of strength and moduli of jointed rocks 总被引：1，自引：0，他引：1
This paper deals with two aspects of jointed rock mass behavior, first the finite element modeling of a jointed rock mass as an equivalent continuum, second the comparison of empirical strength criteria of a jointed rock mass. In finite element modeling the jointed rock properties are represented by a set of empirical relationships, which express the properties of the jointed medium as a function of joint factor and the properties of the intact rock. These relationships have been derived from a large set of experimental data of tangent elastic modulus. It is concluded that equivalent continuum analysis gives the best results for both single and multiple jointed rock. The reliability of the analysis depends on the estimation of joint factor, which is a function of the joint orientation, joint frequency and joint strength.Empirical strength criteria for jointed rocks, namely Hoek and Brown, Yudhbir et al., Ramamurthy and Arora, Mohr–Coulomb have been incorporated in a nonlinear finite element analysis of jointed rock using the equivalent continuum approach, to determine the failure stress. The major principal stress at failure, obtained using Ramamurthy's criteria, compares very well with experimental results. 相似文献
7.
In order to study the damage constitutive model of rock mass with non-persistent joints in engineering practice, the assumption that the rock mesoscopic elements strength obeys the Weibull distribution function of random, the Drucker–Prager criterion is used as a representation method to describe the strength of the mesoscopic elements, and mesoscopic damage variable is deduced. Combined with the energy principle and the fracture damage theory, the macroscopic damage variable formula is deduced considering the crack propagation length and the friction effect of joint closure in the rock mass. Finally, based on the strain equivalent hypothesis of Lemaitre and considering the coupling of macro and micro defects, the composite damage variables are derived. A macro–meso composite damage constitutive model of rock mass with non-persistent joints is established based on the Drucker–Prager criterion. The theoretical constitutive curves of the model are in good agreement with the experimental constitutive curves of the non-persistent jointed rock masses. The considering effects of crack propagation length and joint closure friction effect are compared with those without considering the crack propagation length and joint closure friction effect, which finds that the former is superior to the latter, and the rationality and validity of the model is verified. 相似文献
8.
Development of Rock Bolt Elements in Two-Dimensional Discontinuous Deformation Analysis 总被引：1，自引：0，他引：1
Computer modeling can be used to explore and gain new insights into the impacts of rock bolt intersecting joints in rock masses, and to estimate the effectiveness of the rock reinforcement system. In order to achieve this goal, we couple a rock bolt element into the two-dimensional discontinuous deformation analysis (DDA2D) program. The coupling algorithm is based on the analytically-derived interface behavior between a rock bolt and the rock material for grouted rock bolts. The shear force generated by slippage along the interface is assumed to have a linear relationship with respect to the relative slipping distance between the rock bolt and the rock. The linear elastic criterion is applied to determine the material behavior of rock bolts before the axial stress reaches the yield value. The pullout tests are simulated to verify the coupling algorithm and the effects of the proposed rock bolt elements. Parametrical studies are also carried out to analyze the effectiveness of the rock bolts under various end conditions, joint locations and bond stiffness. In addition, the performance of the rock bolt during the interface debonding is analyzed using two types of constitutive laws, i.e., the friction law and the reduction law. The simulation results show that the proposed rock bolt models can predict the shear forces and axial loading along the rock bolts. 相似文献
9.
针对工程实际中断续节理裂隙岩体的损伤本构模型,假设岩石微元强度服从Weibull随机分布,以摩尔-库仑破坏准则作为描述微元强度的表示方法,推导出细观损伤变量。利用能量和断裂力学理论,综合考虑节理几何特征及力学特性,推导宏观损伤变量计算公式。基于Lemaitre应变等效假设,考虑宏细观缺陷耦合作用,推导出复合损伤变量,建立了基于摩尔-库仑准则的宏细观缺陷耦合作用的断续裂隙岩体损伤本构模型。研究结果表明：（1）采用摩尔-库仑准则作为描述微元强度的统计分布变量建立的损伤模型能够较好地反映岩石内部缺陷分布和变形特征,该模型真实地反映岩石微元强度受应力状态的影响。（2）该模型建立的理论曲线与断续节理岩体的试验曲线吻合较好。（3）节理裂隙岩体宏观损伤变量及峰值强度随节理倾角的变化规律与综合考虑宏细观耦合作用下的损伤变量及裂隙岩体峰值强度随节理倾角的变化规律基本一致。（4）宏细观耦合作用下的等效弹性模量与节理贯通率呈非线性负相关;在节理倾角一定的情况下,损伤变量与节理长度呈非线性正相关;在贯通率较小时,岩体的宏观损伤变量与内摩擦角的关系呈线性负相关变化,贯通率达到一定程度,线性关系变成非线性关系。 相似文献
10.
Rock joint modeling using a visco-plastic multilaminate model at constant normal load condition 总被引：2，自引：0，他引：2
Reza Mahin Roosta Mohammad Hossein Sadaghiani Ali Pak Yaser Saleh 《Geotechnical and Geological Engineering》2006,24(5):1449-1468
Rock joints play an important role in the behavior of rock masses under normal and shear loading conditions. Numerical simulation
of the behavior of jointed rock masses is not an easy task due to complexities involved in the problem such as joint roughness,
joint shear strength, hardening and softening phenomenon and mesh dependency. In this study for modeling purposes, a visco-plastic
multilaminate model considering hardening and softening effects has been employed. For providing the necessary data for numerical
simulation, a series of laboratory experiments have been carried out on regular tooth-shape asperities made by gypsum, under
constant normal load conditions. Shear stress–shear displacement and normal displacement–shear displacement of artificial
joint specimens are simulated using the proposed numerical model at constant normal load condition (CNL). The results indicate
the capability of the model for simulating rock joints behavior in both strength and deformation field. Although the numerical
model has been developed for simulating the behavior of artificial joints, the concept of the method can also be used for
natural rock joints. 相似文献
11.
锚固节理岩体等效力学参数三维离散元模拟 总被引：4，自引：0，他引：4
节理岩体是工程边坡的重要研究对象,通过数值模拟（3DEC）的方法研究了加锚节理岩体的力学特性。以龙滩水电站左岸边坡的锚固设计为例,推导了边坡加锚节理岩体的等效力学参数,进行了岩石数值单轴压缩试验、直剪试验以及岩体结构面直剪试验,对数值试验的结果进行了误差分析和修正,确定出加锚节理岩体的等效力学参数为：岩石的变形模量、内摩擦角、内聚力不变,结构面的内摩擦角不变,内聚力由50 kPa提高到122 kPa。所得结论与采用物理试验的试验结果相符,验证了用数值模拟方法进行岩石力学试验的可行性和可靠性。 相似文献
12.
The formulation of macroscopic poroelastic behavior of a jointed rock is investigated within the framework of a micro–macro approach. The joints are modeled as interfaces, and their behavior is modeled by means of generalized poroelastic state equations. Starting from Hill's lemma extended for a jointed medium and extending the concept of strain concentration to relate the joint displacement jump to macroscopic strain, the overall poroelastic constitutive equations for the jointed rock are formulated. The analysis emphasizes the main differences and similarities of the resulting behavior with respect to that characterizing ordinary porous media. It is shown that, unlike ordinary porous media, conditions on the poroelastic parameters of joints are required for the macroscopic drained stiffness to entirely define the poroelastic behavior. This is achieved, for instance, if the joint network is characterized by a unique Biot coefficient. Extension of the analysis to non‐linear poroelasticity is also outlined. Finally, the theoretical formulation is applied to two particular cases of jointed rock for which explicit expressions of the overall poroelastic parameters are derived. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
13.
针对目前节理岩体损伤本构模型中仅考虑节理等宏观缺陷造成的损伤,而没有考虑岩块中微裂纹等微观损伤的不足,提出了综合考虑宏微观损伤的节理岩体本构模型。其中微观损伤模型采用基于应变强度理论和岩石微元强度服从Weibull分布假定的统计损伤模型,把其应用于被节理切割而成的岩块。而宏观损伤模型主要基于连续介质力学原理,把节理对岩体性质的劣化作为损伤来考虑。在考虑节理传压及传剪系数的基础上,提出了综合考虑宏微观复合损伤的节理岩体本构模型。算例表明宏观节理的存在大大削弱了岩体的强度,降低了其刚度,增大了其柔性。所提出的模型能够较好地反映宏微观两类损伤对岩体应力-应变关系及强度的影响,较为合理。 相似文献
14.
柱状节理岩体原位变形试验力学浅析与模拟 总被引：1，自引：0，他引：1
在白鹤滩坝址区柱状节理岩体原位变形试验成果的基础上,针对节理刚度的取值进行讨论,利用柔性中心孔试验值反算得到柱状节理岩体节理面刚度值。岩体变形是由岩块和节理两部分组成,分析含单节理岩体概念模型的单轴加、卸载规律性和其变形特性,发现其滞回特性是节理力学行为造成的;推导得到了岩体变形计算公式,可用于多组相交节理岩体等效弹性模量的计算,能够反映出节理岩体的各向异性特征;建立了柱状节理随机模型,采用离散元方法和反算的刚度值进行了仿真分析,得到等效变形参数在试验结果范围内。 相似文献
15.
节理岩体蠕变特性研究 总被引：13，自引：3，他引：10
在已知岩石和节理蠕变规律的前提下,推导了节理岩体蠕变模型的一般表达式。假定岩石体积变形和节理法向压缩变形为弹性变形,忽略节理的剪胀现象,认为只有岩石畸变和节理剪切滑移与时间有关,从而推导了含三组相交节理的岩体蠕变模型及其参数。根据反演出的岩石和节理蠕变模型,计算了含三组相交节理的岩体在单轴应力作用下一些节理参数对岩体单轴蠕变的影响。分析表明,节理间距、剪胀系数以及节理夹角都对岩体的单轴蠕变变形有明显影响。节理间距越大,剪胀系数越大,节理夹角越小,节理岩体的单轴蠕变柔量也就越小,岩体的蠕变变形也越小。 相似文献
16.
Strength and dilatancy of jointed rocks with granular fill 总被引：1，自引：1，他引：0
Ashutosh Trivedi 《Acta Geotechnica》2010,5(1):15-31
It is well recognised that the strength of rock masses depends upon the strain history, extent of discontinuities, orientation
of plane of weakness, condition of joints, fill material in closely packed joints and extent of confinement. Several solutions
are available for strength of jointed rock mass with a set of discontinuities. There is a great multiplicity in the proposed
relationships for the strength of jointed rocks. In the present study, the author conceives the effect of increasing stresses
to induce permanent strains. This permanent strain appears as micro crack, macro crack and fracture. A fully developed network
of permanent deformations forms joint. The joint may contain deposits of hydraulic and hydrothermal origin commonly known
as gouge. The joint factor numerically captures varied engineering possibilities of joints in a rock mass. The joints grow
as an effect of loading. The growth of the joints is progressive in nature. It increases the joint factor, which modifies
the failure stresses. The dilatancy explains the progressive failure of granular media. Hence, a mutual relationship conjoins
effectively the strength of jointed rock and a dilatancy-dependent parameter known as relative dilatancy. This study provides
a simple and integral solution for strength of jointed rocks, interpreted in relation to the commonly used soil, and rock
parameters, used for a realistic design of structure on rock masses. It has scope for prediction of an equivalent strength
for tri-axial and plane strain conditions for unconfined and confined rock masses using a simple technique. 相似文献
17.
岩体锚固效应及锚杆的解析本构模型研究 总被引：3，自引：0，他引：3
利用Mohr-Coulomb、Hoek-Brown以及Duncan-Chang理论分别分析了块状和碎块状岩体锚固后的物理效应,通过分析认为,岩体锚固后可以有效地提高岩体的凝聚力和软弱结构面的抗剪强度,增强岩体的弹性模量,改善岩体的力学性质。通过对拉拔试验测试结果分析,在一定的假设条件下,推导了锚杆与注浆体或岩体耦合情况下的解析本构方程,并对其进行了参数分析,认为提高拉拔力、增大锚杆直径和锚固段长度可以有效地改善其锚固效果,并提出了锚固临界值的概念。在前人工作的基础上,利用提出的耦合解析本构模型建立了非耦合状态下锚杆的解析本构模型,通过计算认为,该解析模型是合理的。 相似文献
18.
节理岩体锚杆的综合变形分析 总被引：2，自引：0，他引：2
在总结国内外对节理岩体中锚杆加固机制的试验研究和理论探讨基础上,综合考虑锚杆的切向和轴向变形能力,建立节理锚固锚杆在剪切荷载作用下的变形模型,将节理锚固锚杆的变形区划分为弹性变形段和挤压破坏段,引入表征挤压破坏段长度的变量,对锚杆与岩体的相互作用机制进行理论分析,推导了剪切荷载与剪切位移和轴向荷载与轴向位移的关系。通过分析锚杆的屈服破坏形式,得到了确定挤压破坏段长度的方法。最后,通过算例分析了挤压破坏段长度与锚杆直径、岩体强度、锚固角度等参数的关系,得到了以下结论：（1）节理锚固锚杆抗剪作用的实质是锚杆调动岩体的抗压强度抵抗节理切向荷载。在抗压强度较高的硬岩中,挤压破坏段局限于节理面附近,锚杆影响范围小;而在抗压强度较低的软岩中,挤压破坏段较大,而且会产生较大的剪切变形,锚杆影响范围较大。（2）锚杆屈服破坏形式与岩质和锚杆直径有关。硬质岩体发生剪切屈服,而较软岩体中容易发生弯曲屈服;小直径锚杆一般直接剪切屈服,而大直径锚杆可能发生弯曲屈服。锚杆屈服破坏后出现塑性铰,挤压破坏段范围在节理一侧约为直径的1～2倍,继续增加剪切荷载,挤压破坏段长度不再增大。（3）随岩质的不同,锚杆锚固节理的最优锚固角变化较大。岩质较硬时,最优锚固角度较小,反之则较大。 相似文献
19.
Fracture data available for one of the rock masses (limestone) in the dam site of Yujian River Reservoir were used to build and validate a stochastic 3-D fracture network model, and to perform a REV and equivalent continuum study in 3-D. A number of relations are developed in the paper between the rock mass mechanical parameters and fracture tensor components in 3-D. Based on the mechanical parameter values obtained in every 45° direction in 3-D, the principal parameter values, principal directions and tensors are developed for rock mass mechanical parameters to represent the REV block size properties. An incrementally linear elastic, orthotropic constitutive model is suggested to represent the equivalent continuum pre-failure mechanical behavior of the jointed rock mass by incorporating the effect of joint geometry network by the fracture tensor components. 相似文献
20.
混凝土喷层支护节理岩体等效力学模型及其应用 总被引：1，自引：0，他引：1
考虑喷层在节理面局部的限剪和限裂作用,提出喷层支护节理岩体流变模型,在此基础上推导出喷层支护节理岩体的本构关系,建立了一种喷层支护节理岩体等效力学模型。采用该模型进行结构有限元计算,喷层、节理均不需要离散网格,进行等效模拟;当实际节理裂隙的数量与方向或喷层的厚度变化时,也不需要变化计算网格,从而可降低前处理工作量,为大型复杂结构的计算分析提供较大便利。最后,通过算例和实际工程验证了该模型的有效性--不仅具有离散模型便于模拟喷层真实作用机制的优点,而且具有等效模拟简单易行的优点,具有较好的工程应用前景。 相似文献