Abstract Barton's joint model is the most realistic model for predicting the nonlinear shear behavior of rock joints. This capability comes from the inclusion of a joint surface roughness parameter called the joint roughness coefficient (JRC) that is mobilized under shearing. Recently, a linearized implementation of Barton's model has been done to obtain the mobilized equivalent Mohr-Coulomb (M-C) parameters that account for generation and reduction of JRC as a function of shear displacement ∆ u . These equivalent parameters will allow the linear M-C model to capture nonlinearity in the shear behavior of rock joints. In the linearized Barton's model, the pre- and post-peak joint shear stiffness also contains mobilized JRC that is expressed as hyperbolic and logarithmic functions of ∆ u , respectively. This paper further explores the capability of the linearized Barton model to predict the shear behavior of rock joints. The model is verified against results from the experimental and numerical direct shear test on joint planes from various rock types. The verification shows that the linearized Barton's model can capture the nonlinearity in the shear stress-displacement and in the dilation-induced shear displacement behaviors of rock joints under variations normal stress and JRC values. In the future, the linearized Barton's model has the potential to be applied in computer codes for fractured rock modeling. By implementing this model, neither the simplicity of the linear M-C model nor the advanced capability of the nonlinear Barton's model is lost. 1. Introduction In a fractured rock mass, the shear behavior of rock joints is particularly important because it dominantly controls the deformability, strength, and hence the stability of the rock mass. Block sliding from a slope or block falling in an underground excavation are examples of joint shear behavior that is not only controlled by the shear strength of the particular joint but also by its dilation (Goodman, 1976; Barton, 1982). The dilation is caused by the mobilization of joint surface roughness, causing a nonlinearity in the shear behavior of rock joints in the form of strain hardening and strain softening under shearing.

Abstract The present study evaluates aperture distributions and fluid flow characteristics for variously sized laboratory scale granite fractures under confining stress. As a significant result, the contact area in the fracture plane was found to be independent of scale. By combining this characteristic with the fractal nature of the fracture surfaces, a method for predicting fracture aperture distributions beyond laboratory scale is developed. The validity of the method is revealed through reproduction of the results of the laboratory investigation and the maximum aperture-fracture length relations, which have been reported in the literature. The present study finally predicts conceivable scale dependencies of fluid flows through joints and faults (fractures without and with shear displacement). Both joint and fault aperture distributions are characterized by a scale-independent contact area, a scale-dependent geometric mean, and a scale-independent geometric standard deviation of the aperture. The contact areas for joints and faults are approximately 60% and 40%, respectively. The changes in the geometric means of joint and fault apertures (μm), e m, joint and e m, fault , with fracture length (m), l , are respectively approximated by e m, joint = 1×10 2 l 0.1 and e m, fault = 1×10 3 l 0.7 , whereas the geometric standard deviations of both joint and fault apertures are approximately 3. Fluid flows through both joints and faults are characterized by the formations of preferential flow paths (channeling flows) with scale-independent flow areas of approximately 10%, whereas the joint and fault permeabilities (m 2 ), k joint and k fault , are scale dependent and are approximated as k joint = 1×10 –12 l 0.2 and k fault = 1×10 –8 l 1.1 , respectively.

Abstract Falling head flow tests have been performed to determine the hydraulic conductivity of tension-induced fractures while under normal and shear stresses for eight rock types. The joint roughness coefficients are determined and used to calculate the mechanical aperture. The shear stress is applied while the shear displacement and water head drop are monitored for every 0.5 mm interval of shear displacement. The fracture hydraulic conductivities decrease exponentially with increasing normal stresses. The physical and hydraulic apertures increase with shearing displacement, particularly under high normal stresses. The magnitudes of the fracture permeability under no shear and under peak shear stress are similar. For both peak and residual regions, the physical apertures are about 5 to 10 times greater than the hydraulic apertures. This is probably because the measured physical apertures do not consider the effect of fracture roughness that causes a longer flow path. The difference between the permeability under residual shear stress and that under peak stress becomes larger under higher normal stresses. The findings are useful to determine the rock mass permeability where the fractures are subject to changes of stress states induced by surface and underground excavations.

Abstract It is important to consider the influence of temperature when evaluating the mechanical and hydro-mechanical behaviors of rock masses, since these behaviors are changed by the chemical process at the contact points of the asperities. It is thought that the chemical process is accelerated by heat. In this research, direct shear tests using a slide-hold-slide process in a residual state have been performed under two different temperature conditions using mortar specimens with a single natural rough joint.From the test results, it has been confirmed that the shear strength increased with an increase in the shear holding time in both cases. Moreover, when the rate- and state-dependent friction law was applied to this research, the thermal influence was confirmed.

Abstract This study investigates the cyclic shearing behavior of simulated natural rock samples with three kinds of natural joint surface roughness under different confining pressure conditions. The experimental results contribute to the understanding of various mechanical behaviors and the differences among them after a series of shear cycles. Mechanical properties, such as the Joint Roughness Coefficient ( JRC ), the shear stiffness of the joint after shear, the dilation in the joint during shear, the peak and residual stress levels and the amount of gouge material during shear, were obtained. In this study, the influence of the gouge material obtained after shearing has also been investigated. As from an earlier study conducted by Kishida and Sakurai (2007), it has been proven to have a bearing effect on later cycles, namely, causing a reduction in the residual friction of a joint. The mechanical properties (shear strength, joint dilation, shearing stiffness, peak shear displacement, etc.) depended on the surface roughness of the joint characterized by the JRC , the normal loading applied and the loading cycles. These can be helpful when investigating the weak nature of rock slopes under dynamic loading conditions.

ABSTRACT Mechanical behavior prediction of rock joints is very important in the rock mechanics. Many models have been proposed to predict the mechanical behavior of joints at which lack of correct evaluation of effective roughness coefficient has been the most important shortage. In this research, each of the upper and lower profiles of joint surfaces is considered as a 2-dimensional wave. Then, multi-scale decomposition based on wavelet theory has been applied studying on asperities. Upper and lower profiles have been combined to produce a composite surface having asperities characteristics of both joint surfaces. Each of the composed wave components (roughness and undulation) has been characterized with statistical quantity of arithmetic mean deviation (R a ). This procedure of characterizing for 2-dimensional waves has been easily extended to 3-dimensional joint surfaces. Conformity in the results of shear and dilation modeling and laboratory tests satisfactorily verifies success of the proposed procedure.

ABSTRACT In most of the underground facilities, the existence of water and anisotropic stress are very serious problem in excavating and maintaining the underground open space. Previous studies are not sufficient for estimating the real rock mass behavior with considering the mechanical and hydro-geological aspects. The fractures in situ underground environment are not distributed randomly. Most of fractures in situ occur in a systematic manner with obeying the geologic and tectonic rules. Previous studies are also insufficient for evaluating the history of fracture occurrence and its development. In this paper, we describe about the importance of laboratory experiment, especially useful advantage for adopting True Triaxial Test to investigate the effect of the intermediate principal stress. We focus on the importance of the intermediate principal stress and introduce the observations related to the mechanical characteristics on the wide range of stress state from the confined triaxial compression to confined triaxial extension.

ABSTRACT The evolution of the long-term mechanical, hydraulic, and transport characteristics of rock fractures must be predicted in advance by considering the issue of the underground deposits of the energy by products of high-level radioactive waste. This paper presents slide-hold-slide direct shear experiments conducted for rock salt (halite) specimens with single fractures so as to investigate the effects of load holding on the mechanical properties of rock joints. From the experimental results, it is confirmed that the shear stress reduction can be observed during load holding. It is also confirmed that the shear strength recovery can be observed after load holding and it is found to increase with the increment of load holding period. This is because the dominant factor in the shear strength recovery during holding may be attributed to a purely mechanical process, like creep deformation at the contacting asperities.

ABSTRACT Both mechanical and hydraulic behaviors of rock joints are closely dependent on joint aperture. Understanding how fracture wall-roughness affects fluid flow is important when modeling many subsurface problems. In this paper, a new evaluation method of joint hydraulic aperture using surface asperities height is developed, and the value of hydraulic aperture under different shear displacements is determined using the multi-scale wave decomposition method based on the wavelet theory and some statistical indices. For this purpose, a high resolution laser scanning system is applied. The numerical simulations are based on the experimental data obtained by Sharifzadeh (PhD, Kyushu, 2004) from a series of hydro-mechanical shear tests on natural granite rock joints. Using this method, the hydraulic aperture of joint surfaces has been developed for different shear steps to model the fluid flow of rock joints. The modeling procedure of mechanical aperture (or dilation) is precise and reliable. In addition, the proposed procedure appropriately estimates both hydraulic aperture and fluid flow rate. The conformity in the results of modeling and laboratory tests satisfactorily indicates success of the proposed procedure.

ABSTRACT: This paper deals with in-situ shear strength parameters of rock mass determined by conducting a set of five shear tests in the right abutment drift (Reasi end) and a set of six blocks on the left abutment drift (Katra end) of proposed bridge for Udhampur Srinagar Baramulla Rail Link (USBRL), across Anji, a seasonal tributary of Chenab River, near Reasi. The proposed Anji Bridge is 186m high and 657m long. The shear strength parameter values of cohesion (c) and friction angle (φ) were interpreted by conducting in-situ shear tests for rock to rock interface from five blocks at right abutment and six blocks at left abutment. As the rock mass was jointed and fractured with few shear zones, the shear strength parameters were evaluated only for residual values and peak value could not be differentiated, which was clear from the shear stress versus shear displacement curve. The results of in-situ testing confirmed the rock mass with almost similar shear strength parameters at both the bridge abutments. 1 INTRODUCTION It is proposed to construct an arc bridge for Udhampur Srinagar Baramulla Rail Link (USBRL), across Anji, a seasonal tributary of Chenab River, near Reasi district, Jammu & Kashmir, India. The proposed Anji bridge is 186m high and 657m long. The Schematic view of proposed Anji Khad Bridge is shown in Fig. 1. The Central Soil and materials Research Station (CSMRS) undertook the investigation works of determining the deformability and shear strength characteristics of rock mass required for the design of bridge foundation at Anji Khad (CSMRS 2009). This paper deals with in-situ shear strength parameters of jointed rock mass determined by conducting in-situ shear tests in both right and left abutment drifts of Anji Khad bridge. 2 GEOLOGY 2.1 Geology of the Area Massive to blocky dolomite is exposed along both the banks of Anji Khad below the proposed arch foundation up to a height of 50m with wide range of colours (white, light grey, dark grey and pale brown) and different degrees of weathering (fresh, slightly and moderately) and fracturing (moderately and intensely); rolled-down boulders and chips of dolomitic limestone and limestone with silt and clay material and siliceous limestone. The strata in the area are characterized by prominent one sub-horizontal foliation joint and two sub-vertical joints. The foliation joint strikes roughly N-S and dips 200 to 300 in East direction as shown in Fig. 2. The first joint strikes roughly NE-SW and dips 800 to 850 in NW direction and the second joint strikes SE-NW and dips 600 to 700 in SW direction. A few sub-vertical random joints are also present. The strata have major three sets of discontinuities, which are continuous and persistent. At most of the places, the foliation joint and the other two joints intersect each other forming cubical structure. In weathered and fractured dolomitic limestone and limestone, the average spacing of the foliation joint is 5 to 10 cm and of the other joints is 10 to 15 cm.

SYNOPSIS: Around the world, there are many nuclear power generating stations producing nuclear waste and this necessitates a need for nuclear waste repositories. The repositories will consist of a large system of deposition tunnels caverns and deposition holes. As a consequence of such engineering works the rock mass will deform due to stress changes during excavation. Due to the stiffer rock matrix, most deformation occurs along the joints, in the form of normal and shear strains. These deformations change the void geometry and thereby the joint aperture and fluid flow. GI has during the last decades developed methods for characterization of rock joints and rock masses that have been extensively used for underground works around the world. This includes systematic collection of joint characteristics such as JR, JCS scale dependence, etc. and all the parameters used in the Q-method. These data have been used for extensive numerical modelling, using UDEC-BB and NAP SAC for the planned nuclear waste repositories in England and Sweden. The results have been useful for making decisions during the planning phase, and will also be used for the construction phase. 1. BASIC MECHANICS OF ROCK JOINTS When a jointed rock mass is exposed to mechanical and/or hydro mechanical loads, its total deformation is a sum of the deformation of the intact rock and the joints in the rock mass The deformation of a single joint is controlled by a normal stiffness (kn) and a shear stiffness (ks) which describes the rate of change of normal (σn) and shear (τ) stress with respect to the normal (un) and shear (us) displacement, see Figure 1. The mechanical deformation of a rock joint also affects the void geometry between the surfaces and thereby also the aperture and the fluid flow through the joint. Over the past decades, GI has developed methods for characterization of rock joints (using JR, JCS and r) and rock masses (Barton et al, 1974 [1], and Barton & Bandies, 1990 [2]). A description of all the above parameters, which are considered to be of importance when performing field mapping and core drilling, with examples from India and Norway is given by Basin, 1994 [3]. Index tests to determine JR (tilt tests, pull tests and profiling), JCS (Schmidt hammer tests) and r (tilt tests, pull tests and Schmidt hammer) have been carried out on joints recovered in the drill cores from the planned repository sites in England and Sweden. The GI methods of tilt testing and Schmidt hammer testing are described in detail by Barton and Chou bey, 1977 [4] and by Barton and Bandies, 1990 [2]. 2 HYDRO MECHANICAL BEHAVIOUR OF ROCK JOINTS AND EXPERIMENTAL DETERMINATION OF ROCK JOINT CONDUCTING APERTURE AND SEALING 2.1 Basic behaviour During stress changes in a jointed rock mass, the largest deformation is obtained in the joints. Concurrently the void geometry is changed by deformation of the joints. The void geometry can be described by the aperture, which affects both the joint stiffness and the fluid flow through the joint.

SYNOPSIS: The correct evaluation of shear behaviour of rock mass is important in the design of excavations in rocks, stability analysis of rock slopes, anchored rock slopes and design of rock socketed piles. The shear behavior of rock joints greatly influence by the boundary conditions. Constant normal load (CNL) boundary condition is suitable only for planar rock joints whereas for non planar rock joint Constant normal stiffness (CNS) boundary condition is suitable. Most of the equipment developed in the past, study the shear behavior under CNL boundary condition. Hence, a universal large scale direct shear testing machine for rock is developed and fabricated by authors to study the influence of boundary condition. To study the shear behavior of the rock joints a series of tests were conducted under CNL and CNS boundary conditions at optimum shearing rate, on the non planar modeled rock joint. The test results for the non planar joint indicates that CNS boundary conditions yield a higher peak shear stress than that under CNL boundary condition for the same initial normal stress. A detailed account of deformation behaviour is discussed in this study. INTRODUCTION The correct evaluation of shear behaviour of rock mass is important in the design of excavations in rocks, stability analysis of rock slopes, anchored rock slopes and design of rock socketed piles. There are various factors which influence the shear behavior of rock out of that boundary condition is most important (1). The shear behavior of the planar rock joint is different than that of the non planar rock joint and their influence can be well understand by studying the shear behavior under the constant normal load (CNL) and constant normal stiffness (CNS) boundary condition. The shear behaviour of planar rock joints can be investigated in the laboratory by using a conventional direct shear apparatus where the normal load is kept constant (CNL) during the shearing process. This particular mode of shearing is suitable for situations where the surrounding rock freely allows the joint to shear without restricting the dilation, thereby keeping normal stress constant during shearing process. Shear testing under a constant normal load (CNL) boundary condition is only beneficial for cases such as non-reinforced rock slopes. However, for non planar discontinuities, shearing results in dilation as one asperity overrides another, and if the surrounding rock mass is unable to deform sufficiently, then an inevitable increase in the normal stress occurs during shearing. Therefore, shearing of rough joints under such circumstances no longer takes place under constant normal load (CNL), but rather under variable normal load where stiffness of the surrounding rock mass plays an important role in the shear behaviour. This particular mode of shearing is called as shearing under constant normal stiffness (CNS) boundary conditions. For underground opening or rock anchor-reinforced slopes, shear tests under CNL condition are not appropriate. A more representative behaviour of joints would be achieved if the shear tests were carried out under boundary conditions of constant normal stiffness (CNS).

ABSTRACT During in situ direct shear testing on the Questa mined-rock pile materials, New Mexico, USA, large rock fragments were encountered in the shear box. These large fragments can modify the shear strength and deformational characteristics of the material. To study the role of oversize particles on the results of direct shear tests, laboratory experiments and numerical modeling were conducted. In the experimental study, a shear box 5 cm × 5 cm in size was used. The oversize particle was simulated using stainless steel spheres that were placed along the shear plane. In the numerical investigation, a hybrid discrete-finite element model was utilized where the shear box was simulated by finite elements while the rock pile material was represented by discrete elements. Both experimental and numerical findings suggest that the presence of the oversize particle along the shear plane and at the center of the box causes an increase in the friction angle whereas the cohesion decreases for the material and the range of normal stresses used. 1. Introduction Oversize particles in a direct shear test or a triaxial test can change the shear and deformational characteristics of soil. This subject has been studied by some researchers with emphasis on the role of scalping on the mechanical behavior of rock fill dam material. Hennes [1] investigated the effect of particle size, shape, and grading on the friction angle of dry, rounded gravel and crushed rock. The shear test apparatus was 152.4 mm × 304.8 mm (6- inch × 12-inch) in size. He concluded that with the increase in the maximum particle size, the friction angle increases. The same conclusion was made as some complementary triaxial tests were conducted by this author. Vallerga et al. [2] did not observe any change in friction angle of granular material using traixial tests for the situation that the specimen diameter to maximum particle size ratio was larger than about 15. In the series of tests conduced, a fixed void ratio for the specimens was used irrespective of the maximum particle size. To study the effect of specimen size on the shear strength, several drained triaxial tests on saturated river sand and gravel and quarry material were conducted by Holtz and Gibbs [3]. Very small (34.925mm × 76.2 mm), small (82.55 mm × 206.375 mm), medium (152.4 mm × 381 mm), and large (228.6 mm × 571.5 mm) specimens were tested. Test results on sand samples (passing No. 4 sieve size) compacted at 70% relative density showed similar friction coefficients irrespective of the sample size except for the very small samples that showed marked increase in shear strength. The authors attributed this increase in shear strength to the appreciable coarse sand of 4.763 mm (3/16-inch) maximum size that resulted in a maximum particle size to cell diameter ratio of 0.14.

ABSTRACT Joints play an important role in the behavior of dam under normal and shear loading conditions. Existence of discontinuities such as joints causes reduction of strength and increase of deformability in dam structures. Thus the safe management of dam operation requires a precise evaluation of the dam stability in terms of the shear strength of the concrete lift joint or a discontinuity in the rock mass. The shear strength of these two types of joints is analyzed in this paper. Then the applicability of acoustic emission (AE) in monitoring the shear behavior of joints is discussed. In order to identify shear mechanism of joints the AE source location is evaluated. 1. Introduction One of the most important cases of instability of concrete dams generally results from pre-existing geological features in the foundation such as faults, joints, soft rocks and solution channels, the contact joint between dam body and foundation and joints in dam body. Therefore, stability analyses and assessment in term of shear strength of these weaknesses are essential and form a critical part of the safety assessment. Shearing process of the discontinuities can be divided into two types: constant normal load (CNL) condition, where the normal load acting on the discontinuity remains constant during the shearing process, and constant normal stiffness (CNS) condition, where the normal load varies according to the normal dilation. For studying the joint behavior in dam body and its foundations, it can be considered that, depending on the orientations of the joint sets and their depth, each joint is free to dilate and it is subjected to normal load. Hence, to study these conditions, the most appropriate laboratory experimental shear test set-up is constant normal load (CNL). Besides conventional monitoring techniques using extensometers, strain gages and joint meters, the acoustic emission (AE) monitoring has been experimented in several civil engineering structures. The acoustic emission monitoring can be used, as a supplementary tool, for the assessment of damage and instability of structures during construction and operation. Acoustic Emission is a transient elastic wave that is generated by the rapid release of energy within a material. The current status of structural assessment via the acoustic emission method is that stability is associated by no AE activity, while instability is indicated by varying degrees of AE activity. Obviously, the greater the AE activity, the greater is the degree of instability. In most cases, failure is associated by a large burst of AE activity [1]. When joints (construction joints in concrete or rock joints in foundation) are under loading, once the critical state of shear stress is reached, a certain part of the joint is deformed. The identification of this predisposed stage before total failure is important to reduce the danger of sudden release of deformation energy. This prevention process can be done by AE monitoring.

ABSTRACT Most hydraulic aperture studies are based on rectangular flow system with linear shearing. This study investigates the influence of joint surface roughness on the hydraulic behavior, in the curved shearing surface or a circular joint. The most unique part of the investigation is the shape and configuration of the specimen, which is a set of concentric concrete samples. The hollow cylindrical cement mortars were used to duplicate natural rock joints. Various specimen roughnesses were used in the experiments to analyze the effect of roughness on joint hydraulic behavior. One side of the shearing plane rotated around a fixed axis and water, which flew through two shear planes in radial direction, was monitored. Experimental and numerical hydraulic apertures have been calculated by "Cubic law". The experimental hydraulic aperture has been calculated from laboratory flow rate measurement. The flow data were collected for every 0.5 second with slow angle velocity about 0.4 degree/min. This condition can be considered as stable transition of each asperity. Finite Element Method (FEM), numerical modeling, was used to estimate numerical hydraulic aperture from flow rate data by simulation of the given condition. To get input data for these flow rates, 3D roughness data was acquired from 3D laser profiling instrument. During the experiment, small load about 0.1 MPa was applied to shear surface to simulate vertical stress condition. Experimental and numerical results suggest that hydraulic apertures increase with increments of shear displacement. This result supports the condition that hydraulic apertures can be estimated from the roughness data in shearing mode. Introduction Recent concern about Deep Underground Science and Engineering Laboratory (DUSEL) and nuclear depository has regenerated much interest in understanding of flow conditions in jointed rock. An important aspect of this topic is the evaluation of channel formation with integration of the mechanical properties and hydraulic properties of rock joint, since the hydro-mechanical behavior of rock joint can affect the whole underground structure and its stability. In underground construction, principle stresses might change its orientation due to excavation activities. Thus, rotary shear displacement may occur between blocks of a curved fracture. This scenario indicates that flow in the direction perpendicular to shearing direction can have significant effects on joint stability. However, most of hydro-mechanical experiments have been performed on one direction shearing which is parallel to flow direction. This is primarily due to difficulties involved with experimental work on curved fractures [1, 2, 3]. Only few experiments such as Cheon at el. [4] and Koyama et al [5] were performed on non-planar joints with rotational shearing mode. This study simulates flow through test in the direction perpendicular to shearing surface to evaluate the impact of surface roughness and hydraulic apertures. Working with roughness as a parameter has the benefit of being easily measured and reported in the field. Therefore one can estimate flow in different geometrical conditions. Hydraulic aperture can represent generalized flow rate regardless of the sample size and has been studied by others [6].

ABSTRACT: A cyclic shear testing system was established to investigate the mechanical behaviors of rough rock joints under the cyclic loading conditions. Laboratory cyclic shear tests were conducted for two joint types of Hwangdeung granite and Yeosan marble: saw-cut and splitted tensile joints. Prior to test the roughness of each specimen was characterized by measuring the surface topography using a laser profilometer. Several important aspects of cyclic joint behaviors, such as high peak shear strength and nonlinear dilation in the first loading cycle, different frictional resistance for the reversed shear loading direction, and anisotropic shear behavior and its dependence on the normal stress level were identified from the cyclic shear test results. These features and their variations in the subsequent loading cycles are mainly due to the effect of second order asperities and strength of rock material. It was also observed from experimental results that degradation of asperities under cyclic shear loading also followed the exponential degradation laws for asperity angle and the mechanism for asperity degradation would be different depending upon the shearing direction and the type of asperities. I. INTRODUCTION Joints can significantly affect the mechanical behavior of rock masses. Most of the previous laboratory experiments for the mechanical properties of rock joints have been performed to determine the peak shear strength and the stress-displacement relations under unidirectional shear loading. Little work has been conducted to study the comprehensive rock joint behavior under the cyclic loading condition where the direction of shear load is repeatedly reversed. Hutson and Dowding (1990) suggested an exponential wear equation for joint asperity based on the experimental results using artificial joints of sinusoidal shape. Huang et al, (1993) tested molded joints of saw-tooth shape under cyclic shear loading and validated the theoretical degradation law for joint asperities proposed by Plesha (1987). Jing et al. (1993) investigated the cyclic behavior of natural joints using the replica of natural joint surfaces. Lately Homand et al. (1999) reported the cyclic shear behaviors of rock joints having sinusoidal shape of asperities. However, the experimental test results concerning irregular rough joints with matrix of intact rock properties under cyclic shear loading has not been reported. In this study, a direct shear test system was designed to study the mechanical behavior of rock joint of irregular roughness under cyclic shear loading. A series of cyclic shear tests were conducted using both the saw-cut and the splitted tensile joint specimens of Hwangdeung granite and Yeosan marble. Prior to shear tests, surface topography of joint was measured using 3D laser profilorneter and analyzed statistically. 2. EXPERIMENTAL SETUP AND PROCEDURE 2.1 Testing system and specimens A servo-Controlled direct shear testing machine was designed And attached to MTS 815 loading frame. Both shear and normal loading systems were controlled by MTS controller (TestStar) Fig. 1 shows the schematic diagram of cyclic shear testing system. The loading capacity of the testing system is 250 kN in both the normal and shear directions.

ABSTRACT: For many reasons including the efficient land use, environmental and energy saving issues, the demand for the underground construction is highly increasing. The underground structures include nuclear waste repositories, road tunnels, food storage, and so on. Each one of them is usually designed to have a long life span. Therefore, it is necessary to estimate and investigate the hydraulic and mechanical coupling behavior of rock to assess the long-term stability and the environmental effects. In this study, a torsional shear testing apparatus to characterize the hydro-mechanical behavior of a rock joint was devised. Shear stress was driven by twisting the end of a sample in the torsional shear testing apparatus. The results showed that the torsional shear test underestimated the peak shear strength of a rock joint. It is because the torque is a function of the radial distance from the axis of rotation resulting in the radial variation of the shear stress. Fluid flow through rock joints is mainly dependent on the joint roughness, contact area, initial aperture, etc. To examine the dependency, the relationship between the hydraulic and the mechanical aperture for shear-flow was established by measuring the initial aperture. It showed that the mechanical aperture and the hydraulic aperture increased linearly with the increase of the dilatancy. The difference between the hydraulic and mechanical apertures will describe the deviation from the behavior predicted by the parallel plate model. I. INTRODUCTION Recently, various deep underground utilization, such as storage of oil and radioactive waste disposal sites, has drawn much attention. For the appropriate development of them, it is important to examine and to evaluate the mechanical and hydraulic properties of rock joints. It is well known that the hydraulic properties of a rock joint are strongly controlled by aperture and surface roughness of rock joints. Early attempts to model the hydraulic properties such as cubic law assumed a laminar flow through parallel plates (Bandis, 1985). However, in the real surfaces of rock joints have some roughness, not planar. Thus there are several inconsistencies, such as the applicability of the cubic law and the effect of mechanical aperture on flow in joints. The hydromechanical behavior of deformable rock joints subjected by normal stress was studied by Witherspoon (1981), Cook (1988) etc. and is well understood. Recently, research for the examination of the changes in fluid flow rate with the shear displacement of rock joints was being carried out (Makurat, 1992 and Esaki,1998 and Olsson, 1993). In this study, torsional shear testing apparatus was designed to characterize hydromechanical behavior of a rock joint subjected by normal and shear stress. Prior to the experiments, initial aperture was measured using roughness measuring system. The changes in shear stress and fluid flow rates with shear displacement was observed during shear-flow test, and the relationship between mechanical aperture derived from joint closure model and initial aperture. 2. THEORY 2.1 Fluid Flow in a Single Joint For laminar flow within ideal smooth parallel plates, flow rates are expressed with the following expression.

ABSTRACT: A new constitutive model for the shear behavior of rough rock joints is proposed. Within the framework of the classical elasto-plastic theories, the model incorporates the dilation and surface degradation which are distinct features of rough rock joints, The elastic behavior is represented by the shear and normal stiffness. To calculate the plastic displacements after yielding, the nonassociatted flow rule is applied. Maksimovic's equation and Lee's empirical formula for joint shear strength are used for yield and plastic potential functions. The changes of the joint roughness angle that occurred in pre- and post-peak ranges of shear strength curve were approximated by simple power expressions of accumulated tangential plastic work. A discrete finite interface element, which has 6-node and zero thickness, was developed for implementing the proposed joint constitutive model. In order to evaluate the performance of the model, numerical direct shear tests were carried out. The results of the simulation confirmed that the proposed model could reproduce salient phenomena commonly observed in actual shear test or rock joints, including the shear strength hardening, softening, and dilation phenomena. I. INTRODUCTION The shear strength of rock joints is greatly influenced by the roughness of joint surface. Due to surface undulation, the shear displacement along the joint is accompanied by the increase of the normal displacement. This dilation feature or rough rock joints may play an important role in stabilizing the rock mass in same situations. The constraint of normal deformation leads to the increase in normal stress, which in turn gives the mobilization of shear resistance against sliding. Moreover, the profile of joint surface is subjected to a continuous change during the slip. Therefore, a study to understand the complex behavior of rock blocks formed by a few dominant discontinuities intersecting the rock mass, should be equipped with a numerical model which can reproduce the dilatancy of real rock joints in a simple and effective manner. Considerable efforts have been devoted to explaining the relation between the peak shear strength and the surface topography of joints under compressive normal stresses. The shear strength criteria proposed by Pallone (1966), Ladanyi & Archambault(1970), and Barton & Choubey (1977) are good examples. These criteria, however, can only be used for the purpose of estimating the peak shear strength and thus failed to find their appilcations in describing the hardening and softening phenomena In the pre- and post-peak ranges of the shear displacement - shear stress curve. In 1976, Goodman attempted to make use or the complete normal and shear deformation curve individually in his numerical study of rock joints, but he failed to couple two curves. In 1987, Plesha proposed a more advanced constitutive model that can consider the wear of joint roughness. Plesha's model, however, still require more experimental validation. Based on the Maksimovic's formula for rock joints, this paper proposes an elasto-plastic constitutive model which can capture the pronounced deformation features revealed in the direct shear test.

ABSTRACT: The assessment of the shear strength of rock joints is essential for many rock engineering projects. The shear behavior of rock joints is usually investigated in the laboratory by using a direct shear apparatus, where the normal load is kept constant (CNL) during the shear process. However, they may be quite inappropriate for the situations where the normal stress on the joints surfaces changes considerably during the shear process. In this study, a high-performance direct shear apparatus and computer control system have been developed to accommodate the change in normal stress with dilation under constant normal stiffness (CNS) condition. The shear test results of the artificially prepared joint specimens show that the normal stiffness has a significant influence on the shear strength of joints. 1 INTRODUCTION A rock mass of a site is not continuum and its mechanical behavior is significantly affected by the existing discontinuities, such as bedding, joints, faults and fractures. Therefore, the correct evaluation of the shear strength of rock joints plays an important role in the cases of design of deep underground openings and stability analysis of rock slopes. The shear behavior of joints is usually investigated in the laboratory by using a direct shear apparatus, but mainly under constant normal load (CNL) conditions (Huang, X. et al., 1993). They may be quite inappropriate for the situations where the normal stress on the plane of shear is far from being constant during shearing process, for example, in deep underground openings or in grouted rock anchors. In such cases, a more representative behavior of joints would be achieved if the shear tests were carried out under conditions of constant normal stiffness(CNS). There are several references concerned with the shear test of joints under CNS conditions. However, the normal stiffness is very difficult to be changed according the deformability of the joint surfaces and rock mass because of using the springs or the equivalent beam to apply the amount of stiffness (Brahim,B. & Gerard,B., 1989; Indraratna,B., et al., 1999; Ohnishi, et aI., 1990), and the joint surfaces are easily damaged when the spring is too strong. This study is to develop a new direct shear test apparatus of a joint interface under the conditions of CNL and CNS, and to describe a rational procedure for the determination of the shear behavior of rock joints. The value of the normal stiffness can be set automatically by a computer with the A/D and D/A boards. Shear test of the artificial joint specimens is carried out with the developed apparatus in order to clarify the influence effects of the normal stiffness on the shear strength of joints. 2 DEVELOPMENT OF HIGH-PERFORMANCE DIRECT SHEAR APPARATUS A servo-controlled direct shear apparatus was designed and fabricated for the purpose of testing both natural and artificial rock joints under conditions of CNL and CNS. The loading capacity of machine is 400kN in both normal and shear directions (Fig. 1 and Fig. 2).

ABSTRACT: It is important to investigate and evaluate the stress-deformation relation and fracture behavior of discontinuous surface of rock masses during shear process. Therefore, this paper firstly obtains the residual geometrical information of rock discontinuous surface after block shear test in-situ. through measuring rock discontinuous surface with special-designed laser scanning system. Then, by implanting GIS technology, the topography of rock discontinuous surface can be conserved as digital data in GIS database management system. Furthermore, this paper proposes a new analysis method for simulation of shear process in the rock discontinuous surface through the use of the TIN and GRID models of GIS. The simulating and visualizing results shows that this analysis method can tolerably quantify the change of fracture region and distribution of inner stress during shear process. I. INTRODUCTION It is important to obtain the strength and deformation parameters of rock masses quantitatively for the stability evaluation of rock foundation of structures. However, in-situ shear tests of rock masses, usually conducted in many cases, can only get the macro-data of the strength and deformation parameters through stress-deformation curves. It is not clear to the deformation mechanism, fracture mechanism and rock fracture process inside the rock masses. On the other side, it is difficult for long-term conservation of rock discontinuous surface after block shear tests in-situ. Therefore, it is necessary and possible to conserve rock discontinuous surface, to investigate and evaluate the stress and fracture behavior of fracture surface during shear process, through the use of geographic information system (GIS). In the recent years, as a new information technology, GIS has attracted extensive attention. GIS is described as " an organized collection of computer hardware, software, geographic data, and personnel designed to efficiently capture, store, update, manipulate, analyze, and display all forms of geographically referenced information" (ESRI.1994). Simplistically, GIS is a computer system capable of holding and using data describing places on the earth's surface. The residual geometrical information is rock discontinuous surface after block shear test in-situ. Because rock discontinuous surface is geographically spatial data. GIS can be valuable tools for conservation of rock discontinuous surface and simulation of shear process. This paper firstly obtains the residual geometrical information of rock discontinuous surface after block shear test in-situ, through measuring rock discontinuous surface with special-designed laser scanning system. By implanting GIS, the topography of rock discontinuous surface can be conserved as digital data with GIS database management system. Then, this paper explores the use of the TIN and GRID models of GIS for simulation of shear process in the rock discontinuous surface. The simulating and visualizing results show that the method can quantity the change of fracture region and distribution of inner stress during shear process. 2. MEASUREMENT OF ROCK FRACTURE SURFACE 2.1 Block shear tests of rock masses in-situ The rock masses in this research consist of slate of Mesozonic Jurassic Period, distributed in rock foundation region of an expected construction site in Japan. The block shear tests of rock masses.