Strength of Models of Rock with Intermittent Joints
01 Nov 1970-Journal of the Soil Mechanics and Foundations Division (ASCE)-Vol. 96, Iss: 6, pp 1935-1949
TL;DR: In this paper, a series of triaxial compression tests were carried out on five sample types containing various patterns of preformed intermittent jointing, including axial cleavage and a dilational mode at low confining pressures, shear failure through the plaster, planar and non-planar shear failures partly through plaster and partly along the joints, and the formation of multiple conjugate shear planes at the higher confining pressure.
Abstract: A series of triaxial compression tests were carried out on five sample types containing various patterns of preformed intermittent jointing. The 4-in. square by 8-in. high samples were built up from parallelepipedal and hexagonal blocks of high strength gypsum plaster exhibiting rock-like mechanical properties. Tests were carried out at confining pressures in the range 0 psi to 2000 psi. The seven modes of failure observed include axial cleavage and a dilational mode at low confining pressures, shear failure through the plaster, planar and non-planar shear failures partly through plaster and partly along the joints, and the formation of multiple conjugate shear planes at the higher confining pressures, either exclusively through the plaster or partly through plaster and partly along joints, the averaging process for calculating shear strength first proposed by the Austrian School of rock mechanics.
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01 Jan 2002
TL;DR: The Hoek-Brown failure criterion for rock masses is widely accepted and has been applied in a large number of projects around the world as discussed by the authors, however, there are some uncertainties and inaccuracies that have made the criterion inconvenient to apply and to incorporate into numerical models and limit equilibrium programs.
Abstract: The Hoek-Brown failure criterion for rock masses is widely accepted and has been applied in a large number of projects around the world. While, in general, it has been found to be satisfactory, there are some uncertainties and inaccuracies that have made the criterion inconvenient to apply and to incorporate into numerical models and limit equilibrium programs. In particular, the difficulty of finding an acceptable equivalent friction angle and cohesive strength for a given rock mass has been a problem since the publication of the criterion in 1980. This paper resolves all these issues and sets out a recommended sequence of calculations for applying the criterion. An associated Windows program called "RocLab" has been developed to provide a convenient means of solving and plotting the equations presented in this paper.
1,628 citations
Additional excerpts
...The criterion was derived from the results of research into the brittle failure of intact rock by Hoek [3] and on model studies of jointed rock mass behaviour by Brown [4]....
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TL;DR: In this paper, a simple empirical failure criterion is presented and its application in engineering design is illustrated by means of a number of practical examples, and the authors summarize some of the basic information upon which such simplifying assumptions can be made.
Abstract: Jointed rock masses comprise interlocking angular par- ticles or blocks of hard brittle material separated by discontinuity surfaces which may or may not be coated with weaker materials. The strength of such rock masses depends on the strength of the intact pieces and on their freedom of movement which, in turn, depends on the number, orientation, spacing and shear strength of the discontinuities. A complete understanding of this problem presents formidable theoretical and experi- mental problems and, hence, simplifying assumptions are required in order to provide a reasonable basis for estimating the strength of jointed rock masses for engineering design purposes. This Paper summarizes some of the basic information upon which such simplifying assumptions can be made. A simple empirical failure criterion is presented and its application in engineering design is illustrated by means of a number of practical examples. Des masses jointives de rochers comprennent des particules angulaires enchevetrees ou des ...
641 citations
Cites background or methods from "Strength of Models of Rock with Int..."
...Based on these observations, Hoek and Brown (1980a) experimented with a number of distorted parabolic curves to find one which gave good coincidence with the original Griffith theory for tensile effective normal stresses, and which fitted the observed failure conditions for brittle rocks subjected to compressive stress conditions....
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...Lama and Vutukuri (1978) have presented a useful summary of the results of model studies carried out by John (1962), Muller and Packer (1965), Lajtai (1967), Einstein et al (1969), Ladanyi and Archambault (1970, 1972), Brown (1970), Brown and Trollope (1970), Walker (1971) and others....
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...Hoek and Brown (1980) found that there were definite trends which emerged from the statistical fitting of their empirical failure criterion (equation 3) to published triaxial data....
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...Summary of equations with the non-linear failure criterion proposed by Hoek & Brown (1980b)...
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...Hoek and Brown (1980a) analyzed published data from several hundred triaxial tests on intact rock specimens and found some useful trends....
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TL;DR: The Hoek-Brown criterion was introduced in 1980 to provide input for the design of underground excavations in rock as mentioned in this paper, and it has been applied in many projects around the world.
Abstract: The Hoek–Brown criterion was introduced in 1980 to provide input for the design of underground excavations in rock. The criterion now incorporates both intact rock and discontinuities, such as joints, characterized by the geological strength index (GSI), into a system designed to estimate the mechanical behaviour of typical rock masses encountered in tunnels, slopes and foundations. The strength and deformation properties of intact rock, derived from laboratory tests, are reduced based on the properties of discontinuities in the rock mass. The nonlinear Hoek–Brown criterion for rock masses is widely accepted and has been applied in many projects around the world. While, in general, it has been found to provide satisfactory estimates, there are several questions on the limits of its applicability and on the inaccuracies related to the quality of the input data. This paper introduces relatively few fundamental changes, but it does discuss many of the issues of utilization and presents case histories to demonstrate practical applications of the criterion and the GSI system.
419 citations
TL;DR: In this paper, the authors present the results of biaxial tests performed on physical models of rock with non-persistent joints, and the failure modes and maximum strengths developed were found to depend on, among other variables, the geometry of the joint systems, the orientation of the principal stresses and the ratio between intermediate stress and intact material compressive strength (σ2/σc).
260 citations
TL;DR: In this article, a modified non-linear form of Mohr-Coulomb strength criterion has been suggested in order to overcome two major limitations of this criterion; first, it considers the strength response to be linear, and, secondly the effect of the intermediate principal stress on the strength behaviour is ignored.
209 citations