Abstract Several direct shear tests were commissioned by the author to research the shear strength of bedding partings in fresh shale materials of the Pilbara basin in Western Australia. These samples were selected from one rock unit, i.e. McRae Shale Formation, which is characterized by having an intact strength within the range 20–80 MPa. Only samples of clean natural partings were prepared at the laboratory and then tested by single-stage and multi-stage procedures using a servo-controlled shear box, to ensure the application of constant normal stress throughout each test. This paper presents the comparison between the observed laboratory dilation and the predicted dilation of the Barton-Bandis empirical model. The findings show that the Barton-Bandis model tends to predict a larger dilation than observed. The magnitude of the dilation angle is slightly higher in single-stage than in multi-stage test procedures, and in consequence the dilation corrected friction angle for single stage is normally lower than that determined from multi-stage tests. This means that the Barton-Bandis consistently overestimated the shear strength of the bedding when applying the laboratory determined JRC, JCS and Ø b . These findings are part of the author's research work at the University of Western Australia (UWA). 1. Introduction The Pilbara basin is located in the State of Western Australia, and it is well-known for the occurrence of the enriched Banded Iron Ore Formations (BIF) and form the host rocks within which a large number of open pit iron ore mines have been established. The geology includes a stratigraphical column known as the Hamersley group, with rock units of Archean and Proterozoic age, typically divided by geologists into the Brockman and Marra Mamba Formations (Fig. 1.). The Hamersley rock formations of the Pilbara have generally been well studied due to their significance within the Western Australian iron ore industry. These rock masses are characterized by pervasive bedding which have formed from Archean sedimentary formation processes. These anisotropic rock masses typically include inter-bedded shale, sandstones and banded iron formations. These shale units of the Hamersley group are highly anisotropic with respect to shear strength and therefore the slope stability of most of the mining excavations developed within these formations is controlled by the relatively low bedding shear strength of the shale groups and shale bands, which are the weakest rock types. Shale formations range from fresh to highly weathered and are generally highly fissile when fresh and clayey when weathered. An accurate understanding of the shear strength of these materials is therefore of key importance for assessing the slope stability of these mines.

Abstract When interpreting hydraulic fracturing in low permeable rock such as granite, the effect of fluid infiltration into rock matrix is commonly neglected. There are laboratory experiments of hydraulic fracturing on granite samples indicating the fluid infiltration may play important role in the breakdown pressure. This paper presents a numerical simulation of hydraulic fracturing in low permeable rock with the consideration of fluid infiltration into rock matrix. A 2D Distinct Element Method code UDEC was employed where the polygonal blocks were generated by a Voronoi tessellation feature to provide incipient fractures to consider fluid diffusion into rock matrix. This Voronoi tessellated model was verified to be hydraulically representative as a low permeable rock. The simulations of hydraulic fracturing with varying pressurization rates detected three regimes in terms of the effect of pressurization rate on the magnitude of breakdown pressure, which is generally consistent with that predicted by the existing analytical models. It was demonstrated that the varying breakdown pressure with the pressurization rate can be attributed to the varied flow diffusion conditions in the surrounding rock matrix and associated change of stress at wellbore wall. Extending the flow diffusion length such as cyclic injection mode tends to reduce the breakdown pressure. 1. Introduction There is growing interest in performing hydraulic fracturing in low permeable formation for the economical production of resources and energies. The hydraulic fracturing in low permeable shale plays a critical role in shale gas production (e.g., Clerk et al., 2012). Another emerging application of hydraulic fracturing is to create fluid circulation pathways for extracting deep geothermal energy which is stored in deep crystalline formation (e.g., Legarth et al., 2005). There have been numerous studies involving hydraulic fracturing in low permeable rocks (e.g., Chen et al., 2015) and the infiltration of injection fluid into the surrounding rock has rarely been considered. Some laboratory hydraulic fracturing tests in low permeable rock demonstrated that the infiltration of fluid into the rock and its influence might not be negligible. The hydraulic fracturing experiment on Lac du Bonnet granite showed the penetration of fluid into the rock and its influence on the wave velocities (Falls et al., 1992). Ishida et al., (2004) carried out hydraulic fracturing on granite samples by water and oil injection, and found that the influence of fluid viscosity on hydraulic fracture was mainly caused by the varying fluid infiltration conditions. Recent hydraulic fracturing experiments on Pocheon granite demonstrated the water infiltration could significantly impact hydraulic fracturing behavior and the breakdown pressure was increased with the injection rate (Zhuang et al., 2018).

Abstract Enhanced geothermal system (EGS) has the potential to offer a large amount of clean energy by extracting stored thermal energy from the subsurface. The effectiveness of heat extraction is dependent not only on the permeability of fractured rocks but also on the stability of preexisting and induced fractures. A better understanding of fracture slip in granite during fluid injection is critical to optimize the strategies of hydraulic stimulation. We experimentally investigated the shear behaviors of a sawcut fracture, a gouge-filled fracture, and a natural fracture in Bukit Timah granite in response to fluid injection under a constant normal stress and a constant critical shear stress, respectively. In the most cases, the pore pressure at the injection-induced failure exceeds that predicted by the Mohr-Coulomb failure criterion. This is attributed to the nonuniform distribution of fluid over the fracture plane, which is associated with lower permeability of fracture and host rocks and higher injection rate. The shear behaviors of sawcut and natural fractures show a complex combination of creep and stick before injection failure, which is presumably dependent on the state of asperity contacts. The gouge-filled fracture always creeps preceding the injection-induced failure, because the stiffness of testing system overweighs the critical rheologic stiffness of fracture. For these three fractures, the slip rate at injection failure increases with higher injection rate, releasing more strain energy. The slip rate induced by fluid injection in this study falls within the slip rate range of slow slip events observed in natural faults. 1. Introduction Harvesting heat trapped in igneous rocks offers us an affordable and sustainable solution to reduce our dependence on fossil fuels. Because of the extremely low permeability of igneous rocks, fluid injection has been used to create and/or activate fractures, enhancing the permeability of the host rocks. Besides the permeability evolution of rock fractures, the effectiveness of heat extraction is also dependent on the frictional stability of preexisting and induced fractures, because frictional instabilities of fractures result in seismic events. For example, fluid injection-induced seismicity in an enhanced geothermal system (EGS) in Basel, Switzerland led to the closure of the project (Majer et al. 2007), so did the California project in the United States also aiming at extracting underground geothermal energy (Elsworth et al. 2016). Therefore, a better understanding of the frictional stability evolution of fractures in igneous rocks is of critical importance to optimize the hydraulic stimulation strategy for EGS. The fracture is induced to slip when the shear stress acting on the fracture exceeds the shear strength of it according to the Mohr-Coulomb failure criterion (Zoback 2010) and the effective stress law (Terzaghi 1923). When a fracture starts to slip, the slip can either be seismic or aseismic, depending on the friction rate parameter and relative magnitude of critical rheologic stiffness of the fracture and the stiffness of elastic surroundings (Marone 1998). Specifically, when the friction rate parameter is positive, the fracture is intrinsically rate strengthening and can always slip stably (aseismic), while a fracture with a negative friction rate parameter is conditionally rate weakening, tending to slip unstably (seismic) if the critical rheologic stiffness of the fracture is larger than the stiffness of elastic surroundings.

Abstract Too many required pre-existing fractures (over fifteen) by the HTPF method restrict the wide application under various stress measurement conditions. Considering the shortcomings of HTPF method, a rock mechanics equation to describe the shearing stresses intrinsically present on geological discontinuity planes is established, and at the same time, the least square fitting method and the trial searching algorithm code to determine the frictional coefficient of preexisting fractures are utilized to determine complete stress tensors by inversions. Theoretically, each hydraulic test on every preexisting fracture can help establish two mechanical equations, and then three tests on preexisting fractures can determine a complete stress tensor. However, practically, in order to guarantee the inversion code to be convergent, at least four to five pre-existing fractures are needed. Here, this method is named modified hydraulic testing on pre-existing fractures method, abbreviated as M-HTPF method. The M-HTPF method was applied in a stress measurement campaign in Weifang area, Shandong Province. During this stress measurement campaign, the shut-in pressures determined by the hydraulic fracturing test on pre-existing fractures, and azimuth and dip angle data defined by televiewer logging of five geological fractures were utilized to determine the complete stress tensor. The stress tensor is characterized by: σ 1 =8.85MPa, N58.12 ° W ∠ 14.18 σ ; σ 2 =6.61MPa, N26.2 ° E ∠ -21.54 ° ; σ 3 =5.01, N62.86 ° E ∠ 63.86 ° . The M-HTPF method offers a new access to determine a complete stress tensor using a single borehole. 1. Introduction In 1984, Cornet and Valette proposed that the hydraulic test on pre-existing fractures could be utilized to measure the normal stress on the fracture plane so as to determine in-situ stress tensors. On the first international rock stress symposium, Cornet (1986) named this method to determine in-situ stresses the hydraulic test on pre-existing fractures (abbreviated as HTPF). After that, many scientists applied the HTPF method in different field measurements and compared the application effects between the HTPF method and the Hydraulic fracturing (HF) method, and generally, they got fairly good results. Cornet and Burlet (1992) summarized 8 HTPF application cases in France, and then gave some key points and suggestions for carrying out the campaign of HTPF, which offered lots of reference experiences and cases for the popularization of HTPF. In order to determine in-situ stress in a mountainous region, Cornet et al. (1997) conducted HTPF measurements in an inclined borehole, and they combined a genetic algorithm and a Monte Carlo technique to optimize the inversion procedure, finally they got satisfied stress measurement results. In 2003, Cornet et al. developed new HTPF test equipment, the key downhole component of which is a probe combining electrical imaging with an inflatable straddle packer, and consequently, they can determine the normal stress applied on the tested fracture planes by analyzing both hydraulic and electrical signals observed during shut-in phases simultaneously. At the same time, Haimson and Cornet (2003) jointly published a paper to recommend HF and HTPF methods to determine in-situ stresses, sponsored by the International Society for Rock Mechanics (ISRM). In China mainland, Chinese scientists also used this methods in different engineering cases.

Abstract At present, along with conventional energy sources continually consumed, renewable energy sources are increasingly favored, especially the clean and inexhaustible geothermal resources have been universally valued both at home and abroad. In particular, the Enhanced Geothermal Systems (EGS), which is mainly aimed to exploit the thermal energy of Hot Dry Rock (HDR) at depths of 3 to 10 kilometers underground, has been full of interest to many countries. However, so far there hasn't been an EGS being successfully put into commercial operation because of its shortcomings such as small scale, low efficiency, etc. In this article, in response to the bottleneck of the study on the development of traditional EGS based on drilling technology (EGS-D), a conceptual model of EGS based upon excavation technology (EGS-E) is innovatively proposed and its main components of underground structure are described in this paper. As for ‘High ground stress, High ground temperature and High osmotic pressure’ initial conditions with regards to deep rock mass, the excavation experience, which is worth being learnt from extensive review of previous study as well as practical experience such as the successful excavation of ultra-deep mines in the gold field of South Africa, is summed up. The underground spatial structure that may be reasonable to the so-called EGS-E is being tried establishing. It is expected to provide with a basis for our subsequent numerical modeling. 1. Introduction Currently, seeking and developing clean new energy is the basic energy exploitation strategy, and the clean and inexhaustible geothermal resources have been universally valued both at home and abroad. Geothermal energy is the heat energy mainly generated by the transmutation of radioactive elements in rocks, which is 2.0934×10 18 kJ annually. And the geothermal energy stored at depths of less than 10 kilometers underground was estimated to be 170 million times the amount of heat released from all the coals stored in the earth by Pollack and Chapman in 1977 (Wang Ruifeng, 2002). It can be seen that the reserves of geothermal energy are very considerable. In spite of its advantages of stability, continuity and high utilization coefficient, the scale of the geothermal energy with temperature less than 150 °C at depths of less than 3 kilometers underground is usually too small to maintain the demand for long-term stable electricity production which is mainly hydrothermal and only accounts for 10% of all the geothermal energy stored in the earth (Guo Jian et al., 2014). Therefore, the enhanced geothermal system (EGS) which aims at exploiting the geothermal energy from hot dry rock (HDR) at depths of 3 to 10 kilometers has gradually attracted people's attention.

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 existence or many joints brings about the problems of interaction between joints. In this regard, it is very important to explore the interaction between two joints under shear loading condition. In this study, the shear performance of double joints was studied using the laboratory experiments, where the smooth cleavage joints were generated by sawing off and the rough joints were generated by the Brazilian Split test. The experimental results of double joints of sandstone show that, under lower normal stress the interlayer rock between two joints does not fracture, and the peak shear strength of the specimen is determined by the weaker joint. In contrast, under higher normal stress, the peak shear strength is attained when the tensile fractures initiate in the interlayer rock, and it has also relevancy to the JRC of double joints and interlayer thickness. Additionally, numerical simulation of the double-joint shear tests show that the direction of the cracks trends to be parallel with that of the maximum principal stress, and the stress concentration in the joint surfaces causes penetration between different joints, which leads to a lower strength. 1. Introduction Shear strength of a single joint can be effectively estimated by an empirical formula [1], However, the structural planes or joints in the real rock mass are usually not exist alone, the interaction between different joints has important influence on the overall strength. Yang et al. [2] studied the strength and deformation of rock specimens cut with parallel structures under the uniaxial compression conditions. It indicated that the failure modes of specimens with multiple structures can be divided into three types. The stress-strain characteristics of rock mass with multiple joints based on the double axial compression tests have been conducted by Yoshinaka and Yamabe [3], and the related constitutive equation was established. Through the true triaxial compression tests on large size multi-jointed rock specimens, Reik and Zacas [4] have found that the deformation and failure mode of jointed rock mass are both related to the direction of the joints and the stress state. Kulatilake et al.[5] deemed that the fracture tensor component can be used to establish a nonlinear relationship with the strength of rock mass with many groups of joints. Jaeger [6] and Bray [7] predicted the strength of rock mass containing one or two joints by the principle of stress superposition, and they considered that the weakest structure played a decisive role in the strength of rock mass. Hoek and Brown [8] have also set up a prediction formula of jointed rock mass strength based on the uniaxial compression test. In addition, the numerical simulation method is used to study the mechanical properties of the multi-jointed rock, and the results show that the direction, number and spacing of the structural planes have influence on the overall strength[9]-[11]. Generally speaking, the current understanding of the interaction between different joints is still not enough, especially on the interpenetration between two or more rough joints.

Abstract In this study, the effects of shear rate on the mechanical behaviors of artificial rock joints with regular asperities have been studied by a series of double-shear tests. The adopted simulated material composed of gypsum, quartz sand and water was used to simulate rock joints with regular asperities 0°, 15° and 30°. A number of double-shear tests were performed by using a material testing machine (MTS 819 High Rate Test System) and the rate of shear displacement was controlled in the range of 10 –2 –10 1 mm/sec. A set of the artificial rock joints contained two sliding surface and was tested under constant normal load (CNL) boundary condition, and the range of normal stress was 0.1–0.7 (MPa) applied by a pair of pneumatic cylinders. Experimental results show that the shear displacement curves exist obvious stick-slip phenomenon especially in low shear rate and high normal stress for smooth rock joints. The shear stiffness of the smooth joints normalized by normal stress has a semilogarithmic linear relationship with normalized shear rate. The dilation angle is decreasing with the increasing of normal stress level, and the decreased tendency is evident especially at asperities 30°; however, the trends of dilation angle varied with shear rate are different with asperities 15° and 30° as a result of varieties of failure modes. The increasing tendency of the slope of shear strength envelopes is related to the raising of shear rate. In order to distinguish the influences of normal stress level and shear rate on the failure of regular asperities, the failure area ratio (FAR) is defined as the area ratio of shearing failure part and pre-shearing surface. It is found that the FAR has a tendency to increase with the raising of normal stress level but exist no obvious relation with shear rate.

Abstract With the increasing in the number and expanding the scale of underground engineering in China, increasingly prominent on rock burst disaster. Rock burst is one of the most serious geologic hazards, adversely affecting the safety, economy and productivity of underground engineering construction. High ground stress and its induced frequent rock bursts are major influences of tunnel instability during the survey and design and construction stages. As a major construction of the Jinping II Hydro-power Station on the Yalongjiang River, the deep-buried water transfer tunnels face the problems of rock bursts in hard rock under high geostress. According to the characteristic of the rock bursts in Jinping II Hydro-power Station, the method of preventing the rock burst by rapid stress releasing was put forward. Furthermore, the slit local stress relieving method on the key parts of the wall rock of excavation unloading zone is adopted, the two-dimensional stress state on rock wall can be determined provided gouging of more than 3 narrow slots of different directions on the measured site and measuring the deformation caused by the gouge. The test result shows that the wall rock of underground cavern under various influence factors of blasting load and stress field adjustment of rock mass after blasting, dynamic unloading effect of rock mass is significant. Through the testing and application in water transfer tunnels of Jinping II Hydro-power Station, the rapid stress release method by blasting has proven to be an effective method for preventing and treating rock burst.

Abstract This paper describes the measurement and analysis of the roughness of natural rock joints with the aim of proceeding to their characterisation and comparison. Eight rock joints (corresponding to sixteen surfaces) were scanned with a three-dimensional scanner. This was followed by the description and characterisation of the surface roughness, as well as its reproduction and generation using techniques such as fractal models and Fourier transforms. Shear tests under constant normal load were performed, the joint surfaces were again scanned, and the resulting roughness surfaces were compared allowing the evaluation of asperity breakage and surface wear. One of the joint specimens was tested under several normal stresses, which allowed the estimation of its mechanical characteristics, and was scanned after each test to evaluate the influence of the normal and shear load on the variation of roughness. The scans of the rock joints produced accurate numerical descriptions of their topologies, allowing countless possibilities of future studies, such as the study of the matching of rock joints by the numerical adjustment of bottom and top surfaces, the statistical and geostatistical characterisation of rock joints or the degradation of roughness after normal and shear tests. This paper presents an overview of the research work that is still under way.

Abstract The scale effect of rock joint on anisotropic shear strength behavior is studied by performing direct shear test on cylindrical samples of diameter 90 mm, 180 mm and 270 mm. Total number of asperities varies like 5, 8 and 17 for sample diameter 90 mm, 180 mm and 270 mm respectively. Regular surface morphology of saw tooth shape with asperity angle 20° is kept constant for all samples perpendicular to its strike direction. Strike direction is defined in regular joint along which joint offers least resistance to shear stresses. The direct shear test is conducted under constant normal load (CNL) condition with three normal stresses 150 kPa, 300 kPa and 450 kPa. Because of quarter symmetry of the specimen four direct shear test have been carried out at angle of 0°,30°,60° and 90° and assumed that the same results will be repeated in other quadrants. Results from direct shear tests are recorded in terms of shear stress vs. shear deformation curve along with normal displacement. The graph is used to determine the peak shear strength ( τ max ) and corresponding shear displacement ( d s ), shear stiffness ( k s ) and dilation (δ). Result shows significant scale as well as anisotropic shear strength behavior, deformation characteristics, shear stiffness, cohesion (c), angle of internal friction (ϕ)and joint roughness coefficient (JRC). JRC are calculated by fitting the test results in Barton's joint model. The laboratory investigation shows that JRC have significantly affected by shear direction and scale of joint.

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 The objective of this study is to assess the performance of sludge mixed with the commercial grade Portland cement type I for use in minimizing permeability of fractures in rock. The fractures are artificially made in 3 rectangular blocks of sandstone by applying a line load to induce a splitting tensile crack. The water treatment sludge tested comprises over 80% of quartz with grain sizes less than 75 μm. The results indicate that the mixing ratios of sludge:cement (S:C) of 1:10, 3:10, 5:10 are suitable with water:cement ratio (W:C) of 1:1 by weight. For S:C = 3:10, the compressive strength and elastic modulus are 1.22 MPa and 224 MPa which are similar to those of bentonite mixed with cement. The shear strengths between the grouts and fractures surfaces are from 0.22 to 0.90 MPa under normal stresses from 0.25 to 1.25 MPa. The S:C ratio of 5:10 gives the lowest permeability. The permeability of grouted fractures with apertures of 2, 10 and 20 mm range from 10 –16 to 10 –14 m 2 and decrease with curing time.

ABSTRACT Laboratory flow tests have been performed to assess the effects of normal and shear stresses on the permeability of radial fractures around borehole. The rock specimens are prepared from Phu Kradung sandstone to obtain hollow cylinders having outside and inside diameters of 18.6 and 3.3 cm with a length of 15 cm. The rock is uniform and effectively impermeable. A radial fracture is artificially made by tension inducing method. It cuts through the borehole axis and along the specimen diameter. After applying a constant diametrical loading, the water is injectedunder constant head into the center hole. The fracture permeability is determined for various fracture orientations with respect to the vertical loading direction with 15° apart. The flow tests arerepeated 3 times under each vertical load to assess the permanent closure of the fracture under loading. The diametrical loads are progressively increased from 0.63MPa to 1.85MPa. Finite difference analyses have been performed to calculate the normal and shear stress distributions on the fracture under various orientations. The results indicate that the increases of the normal stresses rapidly decrease the fracture permeability.When the normal of fracture is deviated from the loading direction, the shear stress can increase the fracture permeability. A permanent closure of the fracture is observed as evidenced by the permanent reduction of the fracture permeability measured from the second and third cycles. The changes of aperture, water flow rate, and applied are used to calculate the changes of the fracture permeability. The fracture permeability is in the range between 1 × 10 –18 m 2 and 1.5× 10 –15 m2.

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 appropriate assessment of the strength of a jointed rock mass is a fundamental requirement for the successful design of structures built in or on rock. Due to the complexity of the rock mass, a large number of empirical methods are developed, for its estimation. Its analytical treatment has been tackled mainly by the plane of weakness theory. In this study, an extended plane of weakness theory is applied to a well documented jointed rock physical model. For the failure mechanisms observed in the experiment, the non linear strength envelope provided by this extended plane of weakness theory fits well to the experimental data. 1 INTRODUCTION Rock mass strength estimation belongs to the problems that are too complex to be tackled easily with analytical methods. Complexity is mainly due to fracturing, anisotropy inhomogeneity, and the variety of pertinent modes of failure. Therefore, empirical correlations, that do not need theoretical treatment, are usually employed. They come from the systematic observation of the factors that affect the strength. Analytical methods for the estimation of jointed rock strength have been developed, for the case of sparsely jointed rock masses. The most widely known analytical method for such a purpose is the plane of weakness theory, presented by Jaeger [1]. This method has been extended in order to take into account the roughness of joint surfaces. This extended method is presented and then, both the original and extended theories of weakness plane are applied to a jointed rock physical model. 2 THE EXTENDED THEORY OF WEAKNESS PLANE The original theory of weakness plane (Jaeger, [1]) allows for the analytical evaluation of the anisotropic or equivalent isotropic strength of jointed rock. This theory uses the Mohr - Coulomb failure criterion for the joints. However, this linear criterion is unable to describe adequately the shearing behaviour of rock joints, which are rarely smooth, and their strength is a non linear function of the existing normal stress. Experiments ondiscontinuities have shown that for low normal stresses, the surface roughness causes expansion with shear movement, while for higher normal stresses there is failure of asperities and suppression of any expansion. 3 EXPERIMENTAL EVIDENCE ON DISCONTINUOUSSPECIMENS Various researchers, such as for example, Goldstein et al. [5], Hayashi [6], Lama [7], Brown [8], Einstein and Hirschfield [9], experimented on artificial specimens made by blocks, usually of plaster, arranged in such a way to form a jointed structure. By this procedure, the jointed structure of the specimen is considered to represent the rock mass. For low values of confining stress, shear failures of joints or in intact material, were observed. For higher lateral stresses, the failure was due to the formation of many almost parallel shear planes, mainly within the intact material. The strength of the specimens depended on joint dip, except from the case of high lateral pressures, where the strength of the specimen was nearly equal to that of the intact material. The behaviour of specimens was brittle for low lateral pressures and ductile for higher.

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 Concrete dams which are constructed in narrow gorges on rock formations should be able to sustain the high pressure imposed from the water behind the dam. This pressure is transmitted to the rocks at the abutment and foundation through the concrete dam body. In double curvature concrete dams in which the pressure resulted from impounding is imposed to the abutments, choosing the dam site (from rock mechanics point of view) and recognizing rock properties at the abutments are of paramount importance. One of the most important parameters which have to be considered is the shear strength of contact surface between rocks and concrete in the abutments. In this paper that is resulted from a series of in-situ direct shear tests on four concrete blocks prepared on the rocks inside an excavated gallery at the abutments, the shear strength parameters and peak and residual strengths of the contact surface. 1. Introduction The aim of performing in-situ direct shear test is measurement peak and residual shear strength parameters of a discontinuity in rock as a function of normal load. The discontinuity is generally a main and important joint which may be filled with soft materials. Shear strength parameters, C and φ, in design of rocky structures, particularly stability analysis of rock slopes and also stability of dam foundation are of paramount important. In-situ direct shear test is the simplest method in determining the shear parameters, C and φ, and due to large dimensions of test blocks in compare to laboratory samples, in-situ tests lead to more precise and accurate results. For determining shear strength of concrete to rock contact surface of the abutments of a concrete dam, four series of in-situ direct shear tests have been conducted inside the galleries which have been excavated at the abutments of a concrete dam. 2. General Description of Test System The required equipment for cutting and preparing of test blocks consist of electrical saw, handy cutting tools such as hammer and chisel, solid casts in suitable dimensions and concrete additives. The equipment used for conducting the tests consist of a 200 tones hydraulic jack and two 100 tones jacks for applying normal and shear loads, respectively. These jacks are fed with handy and/or electrical pumps. In order to prevent rotation of blocks under the tests, shear load is applied with a degree of 15 regarding to shear surface so that the load effect line is passing through the center of test block (figure 1). Normal load is also applied regularly and kept exactly normal to shear surface throughout the tests using rollers with low friction. Shear and normal loads are controlled using hydraulic gauges with the accuracy of 0.5 bars. In order to measure normal displacement four mechanical or electrical gauges are used with the accuracy of 0.01 mm or 1 micron, respectively. For measuring lateral and shear deformation 4 gauges of the same type are used. General lay out of the test may be seen in figure 2.