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1.
An Empirical Failure Criterion for Intact Rocks 总被引：1，自引：1，他引：0
Jun Peng Guan Rong Ming Cai Xiaojiang Wang Chuangbing Zhou 《Rock Mechanics and Rock Engineering》2014,47(2):347-356
The parameter m i is an important rock property parameter required for use of the Hoek–Brown failure criterion. The conventional method for determining m i is to fit a series of triaxial compression test data. In the absence of laboratory test data, guideline charts have been provided by Hoek to estimate the m i value. In the conventional Hoek–Brown failure criterion, the m i value is a constant for a given rock. It is observed that using a constant m i may not fit the triaxial compression test data well for some rocks. In this paper, a negative exponent empirical model is proposed to express m i as a function of confinement, and this exercise leads us to a new empirical failure criterion for intact rocks. Triaxial compression test data of various rocks are used to fit parameters of this model. It is seen that the new empirical failure criterion fits the test data better than the conventional Hoek–Brown failure criterion for intact rocks. The conventional Hoek–Brown criterion fits the test data well in the high-confinement region but fails to match data well in the low-confinement and tension regions. In particular, it overestimates the uniaxial compressive strength (UCS) and the uniaxial tensile strength of rocks. On the other hand, curves fitted by the proposed empirical failure criterion match test data very well, and the estimated UCS and tensile strength agree well with test data. 相似文献
2.
Considerations on strength of intact sedimentary rocks 总被引：12，自引：0，他引：12
This study presents the results of laboratory testing of sedimentary rocks under point loading as well as in uniaxial and triaxial compression. From the statistical analysis of the data, different conversion factors relating uniaxial compressive and point loading strength were determined for soft to strong rocks. Additionally, the material constant mi, an input parameter for the Hoek and Brown failure criterion, was also estimated for different limestone samples by analysing the results from a series of triaxial compression tests under different confining pressures. The uniaxial compressive strength (UCS) of intact rocks, as estimated from the point load index using conversion factors, together with the Hoek–Brown constant mi, and the Geological Strength Index (GSI) constitute the parameters for the calculation of the strength and deformability of rock masses. 相似文献
3.
基于一种脆性指标确定岩石残余强度 总被引：1，自引：0，他引：1
岩石的残余强度是岩石力学的重要指标,准确地评价岩石残余强度对于评价地下工程的稳定性以及优化岩体支护设计具有重要意义。基于岩石的三轴力学特性提出一种表征岩石峰后强度衰减行为的力学指标--岩石强度衰减系数,该指标可反映岩石的脆性程度,并提出岩石强度衰减系数与围压关系的幂函数模型。对22组不同成因的岩石常规三轴压缩试验数据进行幂函数模型参数拟合,发现不同岩石拟合所得参数离散性较大,分析其原因主要与岩石矿物组成和岩石结构特征等因素相关。在此基础上提出基于强度衰减方法确定岩石残余强度的方法,分析表明,该方法能够很好地拟合岩石残余强度试验数据,并能反映岩石结构性质对残余强度的影响。 相似文献
4.
Characterization of Strength of Intact Brittle Rock Considering Confinement-Dependent Failure Processes 总被引：1，自引：0，他引：1
As technologies for deep underground development such as tunneling underneath mountains or mass mining at great depths (>1,000 m) are implemented, more difficult ground conditions in highly stressed environments are encountered. Moreover, the anticipated stress level at these depths easily exceeds the loading capacity of laboratory testing, so it is difficult to properly characterize what the rock behavior would be under high confinement stress conditions. If rock is expected to fail in a brittle manner, behavior changes associated with the relatively low tensile strength, such as transition from splitting to the shear failure, have to be considered and reflected in the adopted failure criteria. Rock failure in tension takes place at low confinement around excavations due to tensile or extensional failure in heterogeneous rocks. The prospect of tensile-dominant brittle failure diminishes as the confinement increases away from the excavation boundary. Therefore, it must be expected that the transition in the failure mechanism, from tensile to shear, occurs as the confinement level increases and conditions for extensional failure are prevented or strongly diminished. However, conventional failure criteria implicitly consider only the shear failure mechanism (i.e., failure envelopes touching Mohr stress circles), and thus, do not explicitly capture the transition of failure modes from tensile to shear associated with confinement change. This paper examines the methodologies for intact rock strength determination as the basic input data for engineering design of deep excavations. It is demonstrated that published laboratory test data can be reinterpreted and better characterized using an s-shaped failure criterion highlighting the transition of failure modes in brittle failing rock. As a consequence of the bi-modal nature of the failure envelope, intact rock strength data are often misinterpreted. If the intact rock strength is estimated by standard procedures from unconfined compression tests (UCS) alone, the confined strength may be underestimated by as much as 50 % (on average). If triaxial data with a limited confinement range (e.g., σ3 ? 0.5 UCS due to cell pressure limitations) are used, the confined strength may be overestimated. Therefore, the application of standard data fitting procedures, without consideration of confinement-dependent failure mechanisms, may lead to erroneous intact rock strength parameters when applied to brittle rocks, and consequently, by extrapolation, to correspondingly erroneous rock mass strength parameters. It follows that the strength characteristics of massive rock differ significantly in the direct vicinity of excavation from that which is remote with higher confinement. Therefore, it is recommended to adopt a differentiated approach to obtain intact rock strength parameters for engineering problems at lower confinement (near excavation; e.g., excavation stability assessment or support design), and at elevated confinement (typically, when the confinement exceeds about 10 % of the UCS) as might be encountered in wide pillar cores. 相似文献
5.
为较高精度地评估岩石在不同围压条件下的三轴强度，根据岩石破坏时的主应力差与围压呈上凸的非线性特征，提出负乘方型强度准则。通过将该准则与Mohr-Coulomb准则和Hoek-Brown准则进行精度比较，结果表明，乘方型准则参数对围压变化具有较低的敏感度，且该准则可以更高精度地评估岩石三轴强度。应用公开发表文献中多种不同类型岩石的三轴试验数据，对负乘方型强度准则的适用性进行验证，结果显示，在不同围压条件下，该准则评估的岩石三轴强度与试验强度均非常一致，说明负乘方型准则对评估不同类型岩石的三轴强度具有较好的适用性；同时，通过与目前岩石力学界认为较好的指数型准则的比较，得到两种准则评估的岩石三轴强度平均相对误差MRE均在5%以内，其中负乘方型准则具有更高的精度。该准则可为深部岩石工程开挖与支护等设计提供参考。 相似文献
6.
为建立更符合岩石屈服与破坏机制的强度准则,基于能量转化是岩石屈服与破坏的本质属性,采用试验与理论分析相结合的方法,对岩石屈服与破坏准则进行了研究。以岩石强度与整体破坏准则为基础,通过引入弹性应变能释放分散系数,建立基于弹性应变能强度准则;分别采用M-C准则、Murrell准则、三剪能量准则、统一能量准则、三维H-B强度准则及基于弹性应变能岩石强度准则对盐岩和花岗岩的破坏强度进行了计算。结果表明,基于弹性应变能岩石强度准则的计算结果与试验值比较吻合（尤其是真三轴试验条件下）,并且分析了产生上述结果的内在机制。所建立的强度准则仅需测定常规岩石力学参数（单轴抗压强度与泊松比）,物理力学意义明确,对于定量描述岩石的屈服与破坏特性具有重要的意义。 相似文献
7.
Influence of Loading Rate on Deformability and Compressive Strength of Three Thai Sandstones 总被引：1，自引：0，他引：1
Uniaxial and triaxial compressive strength tests have been performed using a polyaxial load frame to assess the influence
of loading rate on the strength and deformability of three Thai sandstones. The applied axial stresses are controlled at constant
rates of 0.001, 0.01, 0.1, 1.0 and 10 MPa/s. The confining pressures are maintained constant at 0, 3, 7 and 12 MPa. The sandstone
strengths and elastic moduli tend to increase exponentially with the loading rates. The effects seem to be independent of
the confining pressures. An empirical loading rate dependent formulation of both deformability and shear strength is developed
for the elastic and isotropic rocks. It is based on the assumption of constant distortional strain energy of the rock at failure
under a given mean normal stress. The proposed multiaxial criterion well describes the sandstone strengths within the range
of the loading rates used here. It seems reasonable that the derived loading rate dependent equations for deformability and
shear strength are transferable to similar brittle isotropic intact rocks. 相似文献
8.
Omid Saeidi Vamegh Rasouli Rashid Geranmayeh Vaneghi Raoof Gholami Seyed Rahman Torabi 《地学前缘(英文版)》2014,5(2):215-225
A modified failure criterion is proposed to determine the strength of transversely isotropic rocks. Me-chanical properties of some metamorphic and sedimentary rocks including gneiss, slate, marble, schist, shale, sandstone and limestone, which show transversely isotropic behavior, were taken into consider-ation. Afterward, introduced triaxial rock strength criterion was modified for transversely isotropic rocks. Through modification process an index was obtained that can be considered as a strength reduction parameter due to rock strength anisotropy. Comparison of the parameter with previous anisotropy in-dexes in literature showed reasonable results for the studied rock samples. The modified criterion was compared to modified Hoek-Brown and Ramamurthy criteria for different transversely isotropic rocks. It can be concluded that the modified failure criterion proposed in this study can be used for predicting the strength of transversely isotropic rocks. 相似文献
9.
Summary A pillar failure at shallow depth of overburden, featuring the recent formation of subvertical open cracks in the rock was
observed. An extensive laboratory test program including Brazilian tests, uniaxial and triaxial compression tests for obtaining
strength and deformation characteristics of the limestone was executed. Strength from single and multiple failure triaxial
compression tests on intact rock and from tests on small scale rock mass specimens were obtained. Classification of the rock
mass was conducted for use with the Hoek-Brown strength criterion. Numerical analysis shows that the strength of the rock
mass exceeds by far the applied stress, suggesting a stable pillar. This typical rock engineering approach to assess rock
mass stability is shown to be inadequate. 相似文献
10.
A new three-dimensional (3D) Hoek–Brown (HB) failure criterion based on an elliptical Lode dependence is proposed to describe failure of rocks and concrete under multiaxial stress states. This criterion not only inherits all benefits of the classical HB criterion that is developed for the triaxial compression (TXC) of rocks but also accounts for the effect of the intermediate principal stress. It is capable of representing the strength difference between the triaxial extension (TXE) and TXC with the introduction of an additional coefficient k (0.5 ≤ k ≤ 1.0), which can be derived from TXE tests or taken as 0.53 for rocks in cases where the TXE test data is unavailable. Other two material constants (mi and σci) involved in this criterion can be obtained from TXC tests. Additionally, the failure surface of this criterion is smooth and convex on the deviatoric stress plane when 0.5 < k ≤ 1.0. The new criterion achieves very good fit to the test data of TXC/TXE, biaxial compression, and polyaxial compression (PXC) on a wide variety of rock materials and concrete, reported in the literature. Comparison of the new criterion with an existing 3D HB criterion based on the same Lode dependence has demonstrated that the new criterion performs better than the latter for test data of rock and concrete under multiaxial stress states except for PXC test data of one rock type. Finally, the influence of values of k on the accuracy of the new criterion is discussed. 相似文献
11.
This paper compares four different rock failure criteria based on triaxial test data of ten different rock strength data using various statistical methods. Least square, least median square and re-weighted least square techniques are used to determine the best fit parameters utilizing the experimental data that describes the failure state for each criterion. The least median square method could identify the scattered data and these scattered data points are observed at higher confining stress. It was observed that the fitting of failure criteria to different rock strength data depends upon the statistical methods used. The prediction of unconfined compressive strength and failure strength for different rocks estimated using various statistical methods are discussed in terms of different statistical performances of the prediction. 相似文献
12.
Hossein Rafiei Renani C. Derek Martin Evert Hoek 《Geotechnical and Geological Engineering》2016,34(1):297-312
The Christensen criterion, originally introduced in materials science, has a simple mathematical form and uniaxial tensile and compressive strength as the only parameters, making it an attractive candidate for rock engineering purposes. In this study, the applicability of the criterion to rock materials is examined. Explicit equations for application of the criterion under biaxial, triaxial compression, triaxial extension, and polyaxial states of stresses are derived. A comprehensive strength data set including the results of tests on synthetic rock, chert dyke, Carrara marble and Westerly granite is utilized to examine the accuracy of the Christensen criterion to the failure of rock material. The two surprising findings about the Christensen criterion are the zero values of tensile strength and the very low slopes of the failure envelope obtained from fitting analyses for chert dyke and Westerly granite. It is shown that the two problems are interrelated and the values of tensile strength tend to zero to produce higher slopes. It is then mathematically proven that the maximum initial slope of the Christensen failure envelope is limited to 4 in triaxial compression and 2.5 in triaxial extension which is considerably lower than the slope of experimental data. The accuracy of the Christensen criterion was found to be significantly lower than the well-established Hoek–Brown criterion. The circular π-plane representations and brittle-to-ductile transition limits from the Christensen criterion are also inconsistent with the observed behavior of rocks. 相似文献
13.
为考虑中间主应力对岩石极限破坏强度作用,在广义Hoek-Brown强度准则幂率项中添加定量表征中间主应力项,构建新的三维Hoek-Brown强度准则。该准则在主应力空间是通过3个角点外接Hoek-Brown准则包络面的曲六面体,在 空间包络线是幂律型曲线。通过与Hoek-Brown准则、Drucker-Prager准则和Mogi准则分别对4组真三轴压缩强度试验数据的拟合对比分析,探讨其反映中间主应力效应的适用性。结果表明,修正的Hoek-Brown强度准则拟合试验数据效果总体最好,Mogi准则次之,Hoek-Brown准则和Drucker-Prager准则较差。从而修正的Hoek-Brown强度准则最适用于粗面岩、大理岩和花岗岩等硬脆性岩石的真三轴强度预测及中间主应力影响规律描述。 相似文献
14.
采用云石胶黏结岩块的方法制备人工节理面,通过直剪试验获得人工节理面的抗剪强度特性,基于完整和单节理砂岩的常规三轴试验,分析不同倾角（0°,30°,60°,90°）对单节理岩体试样力学响应的影响。结果表明:人工节理面在直剪试验中呈现脆性破坏,其抗剪强度符合M-C准则;不同围压下（2.5,5 0和7.5 MPa）完整砂岩的破坏形态和弹性模量基本相同,峰值强度随围压增大;相同围压下（2.5 MPa）不同倾角单节理岩体的破坏形态、弹性模量、峰值强度均不相同,单节理岩体试样的峰值强度-倾角曲线呈反对号“”形,节理倾角对岩体力学性质的影响明显,其中60°节理岩体试样的强度最低,仅为完整岩石强度的19.7%。推导了过圆柱体试样中心任意斜截面内力的三维计算公式,根据其理论预测所得完整岩石的破裂面角度和60°节理试样的破坏方式均与试验结果相符,其吻合度较传统的二维分析更高。 相似文献
15.
L. Zhang 《Rock Mechanics and Rock Engineering》2008,41(6):893-915
Summary Although the Hoek–Brown strength criterion has been widely used in rock mechanics and rock engineering, it does not take account
of the influence of the intermediate principal stress. Much evidence, however, has been accumulating to indicate that the
intermediate principal stress does influence the rock strength in many instances. Therefore, researchers have developed three-dimensional
(3D) versions of the Hoek–Brown strength criterion. In this paper, three existing 3D versions of the Hoek–Brown strength criterion
are reviewed and evaluated. The evaluation shows that all of the three 3D versions of the Hoek–Brown strength criterion have
limitations. To address the limitations, a generalized 3D Hoek–Brown criterion is proposed by modifying the generalized Hoek–Brown
strength criterion. The proposed 3D criterion not only inherits the advantages of the Hoek–Brown strength criterion but can
take account of the influence of the intermediate principal stress. At a 2D stress state (triaxial or biaxial), the proposed
3D criterion will simply reduce to the form of the generalized Hoek–Brown strength criterion. To validate the proposed 3D
strength criterion, polyaxial or true triaxial compression test data of intact rocks and jointed rock masses has been collected
from the published literature. Predictions of the proposed generalized 3D Hoek–Brown strength criterion are in good agreement
with the test data for a range of different rock types. The difference of the proposed generalized 3D Hoek–Brown strength
criterion from and its advantages over the existing 3D versions of the Hoek–Brown strength criterion are also discussed. It
should be noted that the proposed 3D criterion is empirical in nature because it is an extension of the 2D Hoek–Brown strength
criterion, which is empirical. Because of the non-convexity of the yield surface for a biaxial stress state, the proposed
3D criterion may have problems with some stress paths.
Correspondence: L. Zhang, Department of Civil Engineering and Engineering Mechanics, The University of Arizona, Tucson, Arizona
85721, USA 相似文献
16.
Fissures in natural rocks play an important role in determining the strength, deformability and failure behavior of rock mass. However in the past, triaxial compression experiments have rarely been conducted for rock materials containing three-dimensional (3-D) fissures and the failure mechanical behavior of fissured rocks is not well known due to the difficulty of conducting triaxial experiments on fissured rocks. Therefore in this research, conventional triaxial compression experiments were performed to study the strength, deformability and failure behavior of granite specimens with one preexisting open fissure. Thirty-one specimens were prepared to perform conventional triaxial compression tests for intact and fissured granite. First, based on the experimental results, the effects of the confining pressure and the fissure angle on the elastic modulus and the peak axial strain of granite specimens are analyzed. Second, the influence of the confining pressure on the crack damage threshold and the peak strength of granite with respect to various fissure angles are evaluated. For the same fissure angle, the crack damage threshold and the peak strength of granite both increase with the confining pressure, which is in good agreement with the linear Mohr–Coulomb criterion. With increasing fissure angle, the cohesion of granite first increases and later decreases, but the internal friction angle is not obviously dependent on the fissure angle. Third, nine crack types are identified to analyze the failure characteristics of granite specimens containing a single fissure under conventional triaxial compression. Finally, a series of X-ray microcomputed tomography (CT) observations were conducted to analyze the internal damage mechanism of granite specimens with respect to various fissure angles. Reconstructed 3-D CT images indicate obvious effects of confining pressure and fissure angle on the crack system of granite specimens. The study helps to elucidate the fundamental nature of rock failure under conventional triaxial compression. 相似文献
17.
An empirical failure criterion is formulated by expressing the second invariant of stress deviation at failure as a function of the first invariant of stress, key parameter, and volume. Strength data from Apache Leap tuff specimens are analyzed as a demonstration example. The density variable included as a key parameter for this tuff minimizes the effect of heterogeneity caused by nonuniform distribution of pores, mineralogy, inclusions, welding and grain bonding. The criterion incorporates all principal stresses and the scale effect, and hence allows predicting the strength toward in-situ conditions. The proposed derivation improves the correlations between test results and failure envelope for the heterogeneous tuff. The criterion formulated from the uniaxial and triaxial test data adequately predicts the strengths for biaxial compression tests. 相似文献
18.
Fuzzy and Multiple Regression Modelling for Evaluation of Intact Rock Strength Based on Point Load, Schmidt Hammer and Sonic Velocity 总被引：4，自引：0，他引：4
Summary. Uniaxial Compressive Strength (UCS), considered to be one of the most useful rock properties for mining and civil engineering
applications, has been estimated from some index test results by fuzzy and multiple regression modelling. Laboratory investigations
including Uniaxial Compressive Strength (UCS), Point Load Index test (PL), Schmidt Hammer Hardness test (SHR) and Sonic velocity
(Vp) test have been carried out on nine different rock types yielding to 305 tested specimens in total. Average values along
with the standard deviations (Stdev) as well as Coefficients of variation (CoV) have been calculated for each rock type. Having
constructed the Mamdani Fuzzy algorithm, UCS of intact rock samples was then predicted using a data driven fuzzy model. The
predicted values derived from fuzzy model were compared with multi-linear statistical model. Comparison proved that the best
model predictions have been achieved by fuzzy modelling in contrast to multi-linear statistical modelling. As a result, the
developed fuzzy model based on point load, Schmidt hammer and sonic velocity can be used as a tool to predict UCS of intact
rocks. 相似文献
19.
《地学前缘(英文版)》2018,9(6):1609-1618
Rock properties exhibit spatial variabilities due to complex geological processes such as sedimentation,metamorphism, weathering, and tectogenesis. Although recognized as an important factor controlling the safety of geotechnical structures in rock engineering, the spatial variability of rock properties is rarely quantified. Hence, this study characterizes the autocorrelation structures and scales of fluctuation of two important parameters of intact rocks, i.e. uniaxial compressive strength(UCS) and elastic modulus(EM).UCS and EM data for sedimentary and igneous rocks are collected. The autocorrelation structures are selected using a Bayesian model class selection approach and the scales of fluctuation for these two parameters are estimated using a Bayesian updating method. The results show that the autocorrelation structures for UCS and EM could be best described by a single exponential autocorrelation function. The scales of fluctuation for UCS and EM respectively range from 0.3 m to 8.0 m and from 0.3 m to 8.4 m.These results serve as guidelines for selecting proper autocorrelation functions and autocorrelation distances for rock properties in reliability analyses and could also be used as prior information for quantifying the spatial variability of rock properties in a Bayesian framework. 相似文献
20.
This paper describes the results of the engineering geological investigations and rock mechanics studies carried out at the proposed Uru
Dam site. Analyses were carried out in terms of rock mass classifications for diversion tunnel, kinematic analysis of excavation slopes, permeability of the dam foundation and determination of rock mass strength parameters.Uru
Dam is a rock-filled dam with upstream concrete slab. The dam will be built on the Suveri River in the central part of Turkey. The foundation rocks are volcanic rocks, which consist of andesite, basalt and tuff of Neogene Age. Studies were carried out both at the field and the laboratory. Field studies include engineering geological mapping, intensive discontinuity surveying, core drilling, pressurized water tests and sampling for laboratory testing.Uniaxial, triaxial and tensile strength tests were performed and deformation parameters, unit weight and porosity were determined on the intact rock specimens in the laboratory. Rock mass strength and modulus of elasticity of rock mass are determined using the Hoek–Brown empirical strength criterion. Rock mass classifications have been performed according to RMR and Q systems for the diversion tunnel.Engineering geological assessment of the proposed dam and reservoir area indicated that there will be no foundation stability problems. Detailed geotechnical investigations are required for the final design of the dam. 相似文献