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1.
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
2.
Modeling strategy for jointed rock masses reinforced by rock bolts in tunneling practice 总被引：2，自引：1，他引：1
Shunsuke Sakurai 《Acta Geotechnica》2010,5(2):121-126
This paper deals with the modeling of jointed rock masses reinforced by rock bolts. It is well known that rock bolts are extremely
effective in reinforcing jointed rocks. However, if a continuum approach is adopted for modeling jointed rock masses, it is
often misleading to evaluate the effectiveness of the rock bolts by numerical analyses such as the finite element method.
This may be due to the fact that since no more joints exist in the continuum, the effectiveness of the rock bolts in constraining
the relative displacements along the joints cannot be evaluated properly. In order to investigate the reinforcement effect
of rock bolts, physical model tests were performed in the laboratory. The test results revealed that jointed rock masses should
be modeled as an equivalent continuum after the installation of rock bolts and that the mechanical parameters of the equivalent
continuum should be evaluated by considering the reinforcement effect of the rock bolts. Therefore, the values of the mechanical
parameters differ from place to place in accordance with the relation between joint orientation and rock bolt direction, even
though joint systems are homogeneous. In conclusion, in the continuum approach for modeling jointed rock masses, it should
be emphasized that rock bolts and jointed rock masses should not be modeled separately but should be modeled simultaneously
by considering the reinforcement effect of the rock bolts in constraining joint movement. The modeling of shotcrete reinforced
by steel ribs is also discussed in comparison to the modeling by rock bolts. 相似文献
3.
为了研究锚杆对节理剪切性能的作用机制和模式,开展了锚固节理岩体的实验室剪切试验,模拟了不同强度的岩体在剪力作用下的变形和受力特征,对比了锚杆加固前、后岩体的剪切变形规律,分析了节理岩体强度、预应力及锚固方式对节理的抗剪能力的影响,试验过程中通过应变片测点监测锚杆轴力的变化规律,研究了节理剪切过程中锚杆的轴向受力机制和变形特性。剪切试验完成后,取出剪切变形后的锚杆,统计了变形段长度与各参数之间的关系。通过试验结果分析,剪力-位移曲线存在明显的3个阶段：弹性阶段、屈服阶段和塑性强化阶段,曲线近似呈现双直线特征,弹性段锚杆主要发挥销钉作用;屈服段锚杆的轴向作用开始调动,锚杆同时存在销钉和约束作用;塑性段锚杆不再发挥销钉作用,只是依靠其轴向约束作用限制岩体的变形;曲线表现出韧性增强的剪切性能,这就使得锚杆锚固节理岩体的破坏特性由脆性转变为塑性,从而提高了岩体的稳定性和安全度。节理面的滑动对锚杆产生剪切作用,由于切向变形而产生了附加的锚杆轴向变形,锚杆的轴向应力随着剪切位移的增大呈增长的趋势,变形剧烈区域集中于节理面附近,且距离节理面越近其轴向应力增大越多。 相似文献
4.
节理对卸荷条件下岩体的力学性质有重要影响。通过含2条不同间距预制断续节理岩体的三轴卸荷破坏试验,研究了节理岩体在卸荷应力条件下的应力-应变特征、强度、变形特征、破坏规律及节理间距对岩体力学性质的影响。研究表明：相比于完整岩体,节理岩体卸荷破坏时从峰值强度跌落至残余强度过程中轴向应变较大,为完整岩体的3～4倍,岩体破坏时极限强度明显低于完整岩体,脆性特征不如完整岩体明显;节理岩体卸荷破坏时,变形模量有较大幅度的降低,其降低程度是同条件下完整岩体的6～7倍,节理间距越大,变形模量降低程度越大;与含预制节理岩样三轴加载试验结果相比,节理岩体卸荷条件下破坏程度更为强烈,除剪切破裂面外,沿最大主应力方向分布的不同级别的张性裂隙非常发育,预制节理的间距对岩体破坏形态影响不大。 相似文献
5.
M. Singh 《Rock Mechanics and Rock Engineering》2000,33(2):141-147
Summary ?Deformational behaviour of jointed rocks is governed both by the properties of the joints and the intact rock. The applicability
of a constitutive model to predict the stress-strain behaviour of a jointed block mass is discussed in this note. The stress-strain
curves predicted by the model are compared with the experimental curves from physical model tests. It is observed that the
model predicts the tangent modulus of the mass very closely. The failure strains are, however, underestimated, which may be
due to the constant value of shear stiffness, resulting in linear stress-strain response by the model. The non-linear response
of stress-strain curves can be obtained by using a variable value of the shear stiffness of the joints. A simple approach
has been presented to assign variable stiffnesses, based on direct shear test results on joints. It is found that by assuming
a variable stiffness the axial strains can also be predicted accurately. The transverse strain, however, remains highly underestimated
by the model. 相似文献
6.
Strength and Deformational Behaviour of a Jointed Rock Mass 总被引：1，自引：0，他引：1
Summary
An assessment of the strength and deformational response of jointed rock masses is an essential requirement in the site selection,
design and successful execution of Civil and Mining Engineering projects. A quick estimate of these properties for preliminary
evaluation of alternate sites, will reduce considerable expenditures for field tests. An attempt has been made in the present
study to develop a link between strength and deformability of jointed block masses with the properties of intact specimens,
obtained from simple laboratory tests, taking into account the influence of the properties of the joints. Extensive experimentation
has been carried out on large specimens of jointed block masses under uniaxial compression. The model material represents
a low strength rock. Various joint configurations were introduced to achieve the most common modes of failure occurring in
nature. A coefficient called Joint Factor has been used to account for the weakness brought into the intact rock by jointing.
Methods of computing the Joint Factor for various modes of failure of a jointed mass in an unconfined state have been established.
The effect of Joint Factor on strength and tangent modulus of the mass has been studied and the values have been correlated
with those of intact rock. Guidelines for assessing probable modes of failure of a jointed mass will enable one to estimate
the relevant strength and tangent modulus of the mass. 相似文献
7.
An anisotropic geomechanical model for jointed rock mass is presented. Simultaneously with deriving the orthotropic anisotropy elastic parameters along the positive axis, the equivalent compliance matrix for the deflection axis orthotropic anisotropy was derived through a three-dimensional coordinate transformation. In addition, Singh’s analysis of the stress concentration effects of intermittent joints was adopted, based on two groups of intermittent joints and a set of cross-cutting joints in the jointed rock mass. The stress concentration effects caused by intermittent joints and the coupling effect of cross-cutting joints along the deflection-axis are also considered. The proposed anisotropic mechanics parameters method is applied to determine the deformation parameters of jointed granite at the Taishan Nuclear Power Station. Combined with the deterministic mechanical parameters of rock blocks and joints, the deformation parameters and their variability in jointed rock masses are estimated quantitatively. The computed results show that jointed granite at the Taishan Nuclear Power Station exhibits typical anisotropic mechanical characteristics; the elastic moduli in the two horizontal directions were similar, but the elastic modulus in the vertical direction was much greater. Jointed rock elastic moduli in the two horizontal and vertical directions were respectively about 24% and 37% of the core of rock, showing weakly orthotropic anisotropy; the ratio of elastic moduli in the vertical and horizontal directions was 1.53, clearly indicating the transversely isotropic rock mass mechanical characteristics. The method can be popularized to solve other rock mechanics problems in nuclear power engineering. 相似文献
8.
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
9.
In nature, there exist several forms of anisotropy in rock masses due to the presence of bedding planes, joints, and weak layers. It is well understood that the anisotropic properties of jointed rock masses significantly affect the stability of surface and underground excavations. However, these critical anisotropic characteristics are often ignored in existing uniaxial dynamic failure criteria. This study investigates the effect of a pre-existing persistent joint on the rate-dependent mechanical behaviours of a rock mass using a particle mechanics approach, namely, bonded particle model (BPM), to realistically replicate the mechanical response of the rock mass. Firstly, in order to capture the rate-dependent response of the jointed rock mass, the BPM model is validated using published experimental data. Then, a dynamic strength model is proposed based on the Jaeger criterion and simulation results. To further investigate the dynamic behaviours, the dynamic uniaxial compressive strength (UCS) for anisotropic rock masses with various joint orientations is investigated by subjecting the BPM models to uniaxial compression numerical tests with various strain rate. The proposed dynamic strength model is validated based on numerical simulation results. Finally, the fragmentation characteristics of the jointed rock masses are analysed, which demonstrate that the failure mode affects the dynamic UCS. This is further confirmed by the analysis of the orientations of microscopic cracks generated by the compression loading. 相似文献
10.
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
11.
为探究深部岩体在爆破、开挖等扰动荷载下的力学特性,开展锚固岩体在蠕变-疲劳荷载下的室内试验,并进一步探究其能量演化规律。结果表明：（1）在疲劳荷载作用下,加锚节理岩体比无锚条件下的滞回环面积小,在施加预应力时,其滞回环面积又大幅度减少,说明加锚预应力能有效降低其能量损耗;（2）岩石强度越高,其滞回环面积越小,对应的能量耗散越小,反之能量耗散大;（3）对比不同加卸载速率可知：在每一级循环荷载过程中,加卸载速率越大其对应的应变值、切线斜率就越大。考虑加卸载速率对节理岩体劣化作用,依据应变等价原理,得出节理岩体峰值损伤本构方程,并通过试验验证模型的准确性,为深部岩体结构支护提供思路。 相似文献
12.
13.
Summary Bolting has been used in rock engineering for many years, but present knowledge and research experience supply only limited information concerning the action of rock bolts and the determination of the bearing capacity. To improve this unsatisfactory situation a test-based research programm has been carried out at the Rock Mechanics Laboratory of the Swiss Federal Institute of Technology.Based on recent publications treating rock bolting in theory and practice, about 70 laboratory and field tests have been carried out in order to explain the mode of action of fully-bonded, untensioned rock bolts in stratified or jointed rock masses. A three-dimensional model of a laboratory test was implemented using the Finite Element Method, with the aim to check the test observations and to furnish complete information for all stages of the shear tests.Through a systematic variation of the principal bolting parameters, their influence on the increase of the shear resistance of joints has been quantified. Formulae have been developed for the evaluation of the bearing capacity of fullygrouted bolts and for the prediction of the required shear displacements. 相似文献
14.
Thin layer finite elements are employed to model the response of rock joints in finite element analyses of rock mechanics problems. The case of a circular opening embedded in a rock mass is investigated. Results are obtained for both solid and jointed rock masses, and the effects of the presence of joints on the stress and strain field are investigated. Results from the finite element analysis are verified with respect to measurements from physical modelling. It is shown that the comparison between measured and computed results is satisfactory and that the presence of joints has a pronounced effect on the stress and strain field as compared to that realized in the absence of any rock joints. This study provides valuable data which contribute to the verification of thin layer finite elements for modelling the response of rock joints. 相似文献
15.
In this paper a coupled finite and boundary element formulation is developed for the analysis of excavation in jointed rock. The presence of joints in the rock mass has been included implicitly by treating it as an appropriate anisotropic elastic continuum. The boundary element formulation for an anisotropic medium is briefly discussed. Good agreement has been found between numerical and analytical solutions for several example problems, demonstrating the accuracy of the present formulation. Numerical solutions are also presented for the problems of a deep circular tunnel and a basement excavated in a variety of jointed rock masses. 相似文献
16.
This paper presents a coupled, elastoplastic, finite element and boundary element method for the two-dimensional, non-linear analysis of anisotropic jointed rock. The non-linear and anisotropic behaviour of a jointed rock mass is simulated by representing the mass as an equivalent anisotropic, elastoplastic continuum, so that the influence of the jointing system is ‘smeared’ across the continuum, i.e. the individual joints are not modelled as discrete entities. Numerical examples have been solved to verify the capability, accuracy and efficiency of the present technique. The proposed technique has also been applied to the analysis of tunnel excavation problems in plane strain. The effects of anisotropy and non-linearity of the jointed rock mass during excavation have been investigated in some detail. 相似文献
17.
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
18.
结构面的存在改变了岩体力学性质,影响了岩体强度特征。基于统计岩体力学强度判据,结合摩尔-库仑准则,得到了含单组结构面岩体破坏的4种不同方式和相应的结构面倾角范围,推导了岩体强度由结构面控制转化为应力控制的临界围压表达式。在此基础上,根据岩石和结构面参数之间的关系,将含单组结构面岩体分为4类,并探讨了可能破坏方式和发生破坏的条件。最后,举例分析了含单组结构面闪长岩的强度特征,结果表明,该岩体属于第I类岩体,在垂向受压时先沿结构面后沿岩块破坏,临界围压为9.12 MPa;从全空间分析,该岩体强度各向异性显著,围压增大可使岩体在一些方向上受力时强度由结构控制转化为应力控制。 相似文献
19.
When rock failure is unavoidable, the designer of engineering structures must know and account for the residual strength of the rock mass. This is particularly relevant in underground coal mine openings. Pre-existing discontinuities play an important role in the mechanical behavior of rock masses and thus it is important to understand the effects of such pre-existing discontinuities on the residual strength. For this purpose, the present study demonstrates a numerical analysis using a discrete element method simulation. The numerical results indicate that fracture intensity has no significant influence on the residual strength of jointed rock masses, independent of confining conditions. As confining pressures increase, both peak and residual strengths increase, with residual strength increasing at a faster rate. The finding was further demonstrated by analyzing documented laboratory compressive test data from a variety of rocks along with field data from coal pillars. A comprehensive interpretation of the finding was conducted using a cohesion-weakening-friction-strengthening (CWFS) model. The effect of rock bolts on rock mass strength was also evaluated by using a discrete element method model which suggested that rock bolts can significantly increases residual strength but have limited effect on increasing the peak strength of rock masses. 相似文献
20.
利用编制的计算平面应变压缩岩样轴向、侧向、体积应变及泊松比的FISH函数,采用FLAC模拟了加载速度对剪切带图案及岩样全部变形特征的影响。在峰前及峰后,本构模型分别取为线弹性及莫尔-库仑剪破坏与拉破坏复合的应变软化模型。加载速度较低及适中时,岩样发生单剪切破坏,剪切带倾角及宽度不受加载速度影响,应力-轴向应变曲线及应力与侧向应变曲线软化段的斜率不依赖于加载速度;高加载速度使岩样发生X型剪切破坏,两种曲线软化段较平缓;在相同的轴向应变时,高加载速度使剪切带长度降低。随着加载速度的增加,岩样失稳破坏的前兆越来越明显,当加载速度较高时,前兆反而不明显,这是由于应力存在较大的波动,导致不正确地估计了应力峰值所对应的轴向应变。在应变软化阶段,高加载速度使侧向应变与轴向应变曲线、泊松比与轴向应变曲线及体积应变与轴向应变曲线变平缓,也使体积应变与轴向应变曲线的峰值及对应的轴向应变增加。 相似文献