The shear strength depends on the compressive strength which is itself reduced by the presence of water. Original and practical procedures are developed to numerically process 3d. The reaction for shear load is taken against a concrete pad cast at the upstream face of the drift. Modeling shear strength at low normal stresses for enhanced rock slope engineering, proceedings of the 39th annual highway geology symposium, salt lake city, ut, usa, 346356. Recent drafts of the isrm suggested methods for testing rock joints, and widely circulated errors on the internet and in commercial numerical modelling software, caused the writer to spend some time on the topic of shear strength of rock joints, in his 6th muller lecture barton, 2011. Practical rock mechanics teaches from first principles and aids readers understanding of the concepts of stress and stress transformation and the practical application of rock mechanics theory. Shear strength of rock joints in theory and practice barton. Pdf the shear strength of rock joints in theory and practice.
The contribution of shear reinforcement to shear resistance is typically modeled either with a 45 degree truss plus a concrete term, or a variable angle truss without a concrete term. Among them, the above overburden load is the most important factor. The shear strength of rock joints in theory and practice the paper describes an empirical law of friction for rock joints which can be used both for extrapolating and. Roughness effects on the shear strength of concrete and. Shear strength of unfilled and rough rock joints in. The direction of the shear load is kept the same as anticipated shearing in the structures, in the case of the water. The shear strength along a discontinuity in a soil or rock mass in geotechnical engineering is governed by the persistence of the discontinuity, roughness of discontinuity surfaces, infill material in the discontinuity, presence and pressure of gasses and fluids e. A low strength material for simulation of the mechanical properties of intact rock in rock mechanics models. They are designed to represent the mechanical behavior of the joints with respect to the universal laws of physics. Numerical experimental research on shear strength of rock. This work is intended as a reference text for students and practitioners in mining and rock engineering.
New peak shear strength criteria for anisotropic rock joints. Discontinuities have, indeed, an important influence on the deformational behaviour of rock systems. The behaviour of the rock mass at shallow depth, where stresses are relatively low, is largely controlled by sliding of blocks of rock on joints discontinuities. The choice of a general criterion to determine the shear strength of rough rock joints is a problem that has been investigated for many. Roughness effects on the shear strength of concrete and rock. The shear strength of rock joints in theory and practice, rock mechanics, 10 12, 154. Experimental study of the shear strength of unfilled and rough rock joints 2 1. An alternate approach for deriving rock slope shear. Currently, there is no generallyaccepted theory giving a physical explanation of the shear strength in one and twoway slabs. It is calculated by dividing the applied apparent shear stress by the resulting shear displacement slope of the curve prior to peak shear strength, fig. For example, bedding planes are the result of a repeated sedimentation cycle with a change of sedimentation material or change in structure and texture of the sediment at regular intervals, folding creates joints at regular separations to allow for shrinkage or expansion of the rock material, etc. A model study of the behaviour of steep excavated rock slopes. Lectures on rock mechanicslectures on rock mechanics. Shear strength in one and twoway slabs according to the critical shear cracktheory a.
Rock jointshear strength frictionroughness a series of direct shear tests have been performed in an attempt at assessing the. In general, compared to intact rock, a rock mass has reduced tensile strength almost zero, and reduced shear strength especi ally along discontinuity planes. A brittle model material is developed and used to cast several sets of identical interlocking specimens, which are in turn subdivided into. Shear strength of unfilled and rough rock joints in sliding. The shear strength of rock joints in theory and practice. Other material models such as generalized hoek brown or anisotropic function are available in the material dropdown list. This is due to the strong influence of surface roughness and variable rock strength. The discontinuitys surface topography is often assumed as smooth and straight.
Dynamic shear strength of rock joints and its influence on. Shear strength in one and twoway slabs according to the. In this paper, the highlights and limitations of the existing models used to predict the shear strength behaviour of joints under cns conditions are discussed in depth. Experimental study of the shear strength of unfilled and. Shear strength criteria for rock, rock joints, rock fill and rock masses. In order to study the scale effect of rock joints further, eighteen shear tests at different scales were performed. Experimental studies of scale effects on shear strength.
Experiments conducted earlier showed no clear relationship between mortar compressive and masonry shear strength. In this study, the influence of dynamic disturbance on rock joints was quantified in the form of stress, of which model was established by quasistatic method. Rock mass strength is scale dependent and varies with the volume of rock under. Discontinuities have an important influence on the deformational behavior of rock systems. To quantify this strength, the average elastic modulus of hardened cement pastes with a high watercement ratio wc has been determined by using a homogenization method, in which the bleeding ratio is includes.
Many factors influence the shear resistance of rock joints. The shear strength of rock joints in theory and practice the paper describes an empirical law of friction for rock joints which can be used both for extrapolating and predicting shear strength data. The presence of water is found in practice to reduce the shear strength of rough unfilled joints but hardly to affect the strength of planar surfaces. Standard test method for performing laboratory direct shear. Shear strength of rock joints based on quantified surface. Conversely, under the high effective normal stress levels of interest to. Rock mechanics problemsrock mechanics problems how will rock react when put to mens use. A discontinuity can be, for example, a bedding, schistosity, foliation, joint, cleavage, fracture, fissure, crack, or fault plane.
To overcome nonconsidering roughness of discontinuity, direct shear numerical experiment is proposed to research influences of discontinuous roughness on its strength. The dynamic shear strength of rock joints was analyzed theoretically following the coulombnavier criterion and further investigated experimentally by split hopkinson pressure bar shpb tests with impact velocities of 4. In these earlier tests of vermeltfoort 2010 shear strength increased and mortar compressive strength decreased when more sand was added. Shear strength of rock joints influenced by compacted infill. What is the bearing capacity of rock on surface an at depths. Extension strain and rock strength limits for deep tunnels, cliffs, mountain walls and the highest mountains.
Nonlinear shear strength for rock, rock joints, rockfill. This result is also predicted by the proposed criterion for peak strength. Four new strength criteria which take the following general form are suggested for modelling the anisotropic peak shear strength of rock joints at low normal effective stresses 00. Prediction of the peak shear strength of sandstone and. Rock joints exhibit a wide spectrum of shear strength under the low effective normal stress levels operating in most rock engineering problems.
A series of analytical expressions was developed in the companion paper to describe in detail the shear behavior of regular triangular concreterock joints. This title covers the fundamental properties of rock joints, the method of laboratory testing of rock joints, and shear strength assessment under different loading conditions. The shear strength o rock joints in theory and practice. Introduction the stability of underground mine excavations, tunnels, open pit slopes and others in a jointed rock mass is influenced by the shear strength characteristics of the joints. What is the response of rocks under dynamic earthquake type loading. Shear strength of rock joints in theory and practice. A relationship between joint roughness and joint shear strength. In members with shear reinforcement, a large portion of the shear is carried by the shear reinforcement after diagonal cracking occurs. Simplified shear design of structural concrete members. Practical rock mechanics 1st edition steve hencher. During the test, the tangential force, t, recorded, to displace one part of the joint is recorded together with the actual displacement w. Introduction the stability of underground mine excavations, tunnels, open pit slopes and others in a jointed rock mass is influenced by the shearstrength characteristics of the joints. Experimental studies of scale effects on shear strength, and. Shear behavior of regular triangular concreterock joints.
However, in order to evaluate the relevancy and accuracy of these expressions, a detailed laboratory test program was undertaken with the conditions of each test maintained as closely as. A rubber moulding system is used to obtain impressions of the roughness from a variety of natural joint surfaces. The effect of scale on shear strength is studied by performing direct shear tests on different sized samples of large joints. A discontinuity in geotechnical engineering in geotechnical literature often denoted by joint is a plane or surface that marks a change in physical or chemical characteristics in a soil or rock mass. Interpretation of shear strength parameters of rock mass 230 reaction pad cast at the crown. This paper investigates the effects of joint roughness on shear strength based on experimental data obtained from shear tests on 18 specimens presenting an unbonded contact interface, i. In this paper, the highlights and limitations of the existing models used to predict the shear strengthbehaviour of joints under cns conditions are discussed in depth. Rock joint shear strength frictionroughness a series of direct shear tests have been performed in an attempt at assessing the. A division is made between mechanical and integral discontinuities.
Pdf the shear strength of rock joints in theory and. Rock joint and rock mass shear strength geoslope international. Analysis of shear strength of rock joints with pfc2d 3 1 introduction rock engineering could be considered as the most fascinating field of engineering, and for sure is one of the most dated. Shear resistance of rock joint under nonuniform normal stress. Furthermore, if a rock mass is cut by directional joint sets, the rock mass strength is anisotropic. Pervasive discontinuities joints, bedding planes, shear zones, fault zones, schistosity in a rock mass, and genesis. Firstly, based on researched mechanical properties of discontinuity, the laws how asperity inclination angles and asperity. Choubey, the shear strength of rock joints in theory and practice, rock mechanics felsmechanik mecanique des roches, vol.
Shear strength criteria for rock, rock joints, rockfill and. Apr 19, 2019 this paper investigates the effects of joint roughness on shear strength based on experimental data obtained from shear tests on 18 specimens presenting an unbonded contact interface, i. Standard test method for performing laboratory direct. Shear strength deterioration of rock joints and its induced instability of key blocks subjected to dynamic disturbance constitute the mechanism of many geological disasters such as rockburst, landslide, and rockfall. The choice of a general criterion to determine the shear strength of rough rock joints is a general problem that has been investigated for many years.
The formulas can easily be input into a spreadsheet and the data pasted into a shearnormal function. Apr 22, 2017 there are very few studies on the peak shear strength of cementinfilled joints, despite it being a key parameter in the grouting technique. The shear strength of rock joints in theory and practice, rock. Barton, nr 1976, the shear strength of rock and rock joints, international journal of rock mechanics and mining sciences, vol. The paper describes an empirical law of friction for rock joints which can be used both for extrapolating and predicting shear strength data. Original and practical procedures are developed to numerically process 3d profiles of laserscanned. This paper will introduce a simple general theory for predicting the shear strength of reinforced and prestressed concrete members either with or without shear reinforcement. Pervasive discontinuities joints, bedding planes, shear zones, fault zones, schistosity in a rock mass, and genesis, crystallography, texture, fabric, and other. The shear strength of rock joints in theory and practice 3 however, filled joints containing soft plastic materials such as clay, and faults containing gouge or breccia will not be included, since they constitute a rather special set of problems. The third nonlinear shear strength criterion for rock joints was developed first from unweathered tension fractures, and had.
There are very few studies on the peak shear strength of cementinfilled joints, despite it being a key parameter in the grouting technique. Analysis of shear strength of rock joints with pfc2d. While the peak shear strength shows nonlinear relationship with normal stress, linear superposition cannot be used to calculate the overall. Shear strength criteria for rock, rock joints, rockfill. All these index values can be measured in the laboratory. This text can help ensure that ground models and designs are correct, realistic, and produced costeffectively. The sheared replicas of rough tension fractures are sheared and dilated as tested barton, 1971, barton, 1973. Oct 14, 2011 the effect of scale on shear strength is studied by performing direct shear tests on different sized samples of large joints. The uneven thickness of the overburden causes the joints to be subjected to the nonuniform distribution load.
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