Abstract Drilled shafts or bridge piers can transmit huge structural loads (both axial and lateral) through the overburden soil to the underlying rock mass. Drilled shafts are usually socketed into rock to increase their axial and lateral load carrying capacity. The part of the shaft, drilled inside rock, is called the socket length. Drilled shafts have become an appropriate and economical foundation solution for heavily loaded structures. Although axial load carrying capacity of a rock-socketed pile has been extensively studied, there are still some gaps in understanding the lateral load behaviour of a rock-socketed pile mainly because of the scarcity in field load test data available. An alternative way to minimize this gap is to take help of numerical modelling which can simulate the near-field conditions. For this, in this present work, a two-dimensional distinct element code, UDEC has been used for the discrete element modelling of a single pile socketed in jointed rock mass. Two lateral load field test results from previously published research have been validated by the established numerical model. This validation work is followed by parametric studies of a laterally loaded pile having aspect ratio or socket length to pile diameter ratio of 6 and 12 embedded in a sloping rock mass profile with two sets of joints dipping at different angles (0/90 degree, 15/105 degree, 30/120 degree, and 45/135 degree) from the horizontal. From the results of the parametric studies, non-linear P-y behaviour of the rock-socketed pile on a sloping ground has been formulated. These P-y response curves provide rock resistance as a function of lateral deflection of the pile inside rock. The effects of presence of two joint sets and their dipping angles on P-y behaviour of the pile with two different aspect ratios embedded in a sloping ground have been recorded. These parametric analyses will help in the best design of a laterally loaded pile foundation in sloping jointed rock mass. 1. Introduction A drilled shaft can transmit huge structural loads (both axial and lateral) through the overburden soil to the underlying rock mass. Drilled shafts have many synonyms, such as bored piles, drilled piers, drilled caissons, or cast-in-situ piles. Drilled shafts are usually socketed into rock which in turn, increases its axial and lateral load bearing capacity. The length of the shaft, drilled into rock, is termed as the rock socketed part. The drilled shaft may also be entirely embedded in rock where there is no sub-soil. A representative diagram of a usual drilled shaft, with some of its length socketed into a jointed rock is shown in Fig. 1.

ABSTRACT To provide a practical tool to estimate the rock mass strength for use with the Hoek-Brown failure criterion, the GSI system was introduced. A GSI value is determined from a chart based upon the structure interlocking and joint surface conditions. Continuous fractures usually occupy only a part of the surface of the joint plane within a given rock volume. In jointed rock masses, rock bridges exist due to the non-persistent nature of joints. However, joints are often assumed to be fully persistent for stability analysis of rock structures such as tunnels or slopes. This oversimplification may lead to an overestimation of the number of removable blocks near the excavated face, resulting in excessive expenditure on the rock support. The objective of this study is to analyze how joint persistence will increase the overall rock mass strength in jointed hard rock masses; the study will focus on the influence of joint persistence on the residual strength of rock bridges. An equivalent rock mass strength, considering joint persistence, is obtained analytically and compared with the results from the numerical analysis. Correlation analysis is then performed to relate the rock mass strength to the characteristics of joint persistence and the results are compared to those from the GSI system considering joint persistence. As a result, GSI can vary by as much as 30% depending upon joint persistence.

Abstract: This paper outlines the nature of the Large Open Pit Project, why it was formed, and the research it is pursuing to achieve its objective of expanding the slope design practitioner's knowledge base and improving the reliability of rock slopes in large open pit mines. 1. INTRODUCTION The Large Open Pit Project is an international research and technology transfer project on the stability of rock slopes in open pit mines. Planning for the project commenced early in 2004 when a scoping document outlining a draft research plan was submitted by CSIRO Australia (the Australian Commonwealth Scientific and Industrial Research Organisation) to a number of potential Sponsors for appraisal. An inaugural Project Sponsor's meeting was then held in Santiago, Chile, in August 2004, when the proposal was examined in detail by mining company representatives and a number of senior practitioners and consultants from across the open pit mining industry. Strong, positive responses to the proposal lead to the official commencement of the Project in April 2005. Ground stability and wall slope design are fundamental variables in the economics of operating large open pit mines. For the stakeholders, which includes the owners, mine management, the workforce and the regulators, the end goal is to achieve reliably engineered mine slopes that, if they do fail, do not cause loss of life, equipment damage, sustained losses of production, or the inability to achieve published reserves. Over the last ten to fifteen years these requirements have been hampered by critical gaps in our knowledge and understanding of the relationships between the strength and deformability of jointed rock masses and the likely mechanisms of failure. These shortcomings have been exposed by a number of spectacular slope failures that have resulted in multiple fatalities, production losses and unfavourable world-wide publicity. In turn, these undesirable events demonstrated a pressing need for innovative mining geomechanics research that stepped outside of the box and reassessed the fundamentals of rock mass strength and slope failure mechanisms from first principles. The challenge of stepping outside of the box and reassessing the fundamentals of rock mass strength and slope failure mechanisms from first principles was the driving force that created the LOP Project. The research plan developed for the project focussed on three elements: preparation and publication of an authoritative new generation pit slope Design Guidelines book that clearly outlined for today's practitioners what is the best approach to satisfy best practice at every stage of planning and operating an open pit mine; the effective use of geological and geotechnical data in assessing the strength and deformability of jointed rock masses and the likely mechanisms of slope failure; and hydrogeological studies to assess the effect of pore water pressures on the stability of closely jointed rock. The purpose of this keynote address is to outline the nature and impact of these three elements on the slope design process and how they are helping to expand the slope design practitioner's knowledge base and improve the reliability of rock slopes in large open pit mines.

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.

Abstract: The behaviour of rock mass is largely influenced by the in-situ anisotropy and is different from other engineering materials. The assessment of the strength and deformation of rocks is essential for engineering design and analysis. The dynamic modulus of elasticity is very important when dealing with the problems like blasting. Field tests to determine these parameters directly are time consuming and expensive. Therefore, several authors have proposed empirical relations for estimating the rock mass deformation modulus on the basis of classification schemes. This paper presents the study on the strength and deformation characteristics of jointed rock by conducting laboratory tests on cylindrical specimens of plaster of Paris (POP) by introducing artificial joints, under static and dynamic conditions. Cylindrical specimens of POP mixed with Portland cement to simulate rock of higher strength were also tested. The specimens having one to four joints at inclinations varying from 0o to 90o were tested for both static and dynamic properties. The laboratory results were presented as stress-strain plots and were examined to understand the effect of joint frequency and joint inclination on the strength and deformation behaviour of jointed rock mass. In this paper the compressive strength/elastic modulus of the jointed rock mass was estimated as a function of intact rock strength/modulus and joint factor. The joint factor reflects the combined effect of joint frequency, joint inclination and joint strength. Therefore, having known the intact rock properties and the joint factor, jointed rock properties can be estimated. The test results indicated that the rock mass strength decreases with an increase in the joint frequency and a sharp transition was observed from brittle to ductile behaviour with an increase in the number of joints. It was also found that the rocks with planar anisotropy exhibit the highest strength in the direction perpendicular to the anisotropy and the lowest at an inclination of 30o-45o in jointed samples. The anisotropy of the specimen influences the dynamic elastic modulus more than the static elastic modulus. The results were also compared well with the published works of different authors for different type of rocks. INTRODUCTION The behaviour of rock mass is largely influenced by the in-situ anisotropy and is different from other engineering materials. The assessment of the strength and deformation of rocks is essential for engineering design and analysis. The deformation modulus of a rock mass is an important input parameter in analysis of rock mass behaviour. Field tests to determine this parameter directly are time consuming and expensive. Therefore, several authors (references) have proposed empirical relations for estimating the rock mass deformation modulus on the basis of classification schemes. There are two elastic moduli, namely, static and dynamic. According to Ciccitti and Mulargia (2004) the values of the static modulus, in general, are 5–10% lower than those of dynamic moduli. The dynamic modulus of elasticity is very important when dealing with the problems like blasting. Cylindrical specimens of POP mixed with Portland cement to simulate rock of higher strength (wall strength) were also tested.

SYNOPSIS The paper presents the elastic and elasto-plastic analyses of a gravity dam on jointed rock foundation using distinct element method. The Universal Distinct Element Code (UDEC) is used for carrying out the dam foundation analysis. A concrete gravity dam of 85 m height and 72 m base width is analyzed under loading conditions A and B as per IS-6512 (1984). A total of 26 cases have been analyzed and the behaviour of the dam founded on the jointed rock mass in comparison with the intact rock is studied. It is inferred from the analyses that the presence of joints and joint inclination has a pronounced effect on the stress-deformation response of the dam-foundation system. The deformation of the crest is maximum when the joint inclination is horizontal under loading condition A. Under loading condition B; the crest deformations are maximum when the joint inclinations are between 75° to 105°. The stress-deformation response of the dam on the intact rock and jointed rock is presented in the paper. 1.0 INTRODUCTION The rapid development of water resources in a country necessitates the construction of dams for water storage, flood control and power generation. The foundation of a dam is a critical structural component and requires special attention throughout the lifetime of the project. The foundation has a threefold function, namely to provide stability, to provide sufficient stiffness for limiting the deformations of the dam-foundation system and to provide control of seepage (ICOLD, 2005). If any one of these functions is satisfied only marginally, the performance of the dam is jeopardized. The construction of gravity dam requires a foundation of competent rock with high bearing capacity and resistance to percolation as these structures are sensitive to foundation deformations. With more and more ideal sites being exhausted, it is inevitable that less favourable foundations are to be used for dam construction. Proper design involving a complete stress-deformation analysis is required for dams constructed on rock formations exhibiting material non-homogeneity, anisotropy and non-linear behaviour. The presence of foundation weaknesses such as joints, faults and shear seams cause excessive deformations which are inconsistent to the usual assumption of linear elastic and homogeneous nature of the foundation medium. Presence of discontinuous zones substantially affects the distribution of stresses in the dam-foundation and the overall stability of the system. Joint inclinations also have a marked effect on the deformation pattern and the distribution of stresses. For dams on rock foundations, a critical requirement in the stability analysis is the identification of planes of weakness or discontinuities that combine to give a kinematically possible sliding block mechanism. Failure to identify potential blocks may have disastrous consequences, e.g. the Malpasset dam (Londe, 1987). Numerical models, particularly finite element models, are routinely used in the analysis of the global mechanical and hydraulic behaviour of dam-foundation system under normal operating conditions. Discontinuities may be modelled finite element analysis by incorporating special interface elements to simulate the behaviour of joints, shear zones and faults.

Abstract: This paper updates the recent development of rock dynamics research conducted by the Underground Technology and Rock Engineering (UTRE) research program in Nanyang Technological University, Singapore. It includes dynamic tests for granite rock specimen and various artificial rock joints, development of numerical manifold method and its application in rock slope stability analysis, stress wave propagation in jointed rock mass, and prediction of ground motions induced by underground explosion, etc. It has been found that the rock strengths including uniaxial/triaxial compression, shear and tensile splitting strengths all depends on the strain rate applied to the specimen. To analyze dynamic deformation of rock masses, the numerical manifold method has been extended to a three dimensional version and various slope stability problems have been studied. A visco-elastic equivalent medium model has been put forward to analyze stress wave propagation in jointed rock mass. It is validated that the proposed equivalent medium model gives more reasonable results in describing wave transmission and attenuation in jointed rock mass. A virtual wave source model is proposed to consider the wave reflections at rock joints. Wave propagation theory by adopting the principle of momentum conservation is used to predict the ground motion induced by an underground explosion. It is found that the analytical solution gives an accurate prediction of the ground motions in terms of peak ground motions and wave forms. 1. INTRODUCTION Rock dynamics is one of the strategy research areas of the Underground Technology and Rock Engineering (UTRE) research program in Nanyang Technological University, Singapore. The UTRE is a long term joint research program between Nanyang Technological University (NTU) and Defence Science and Technology Agency (DSTA), Singapore. The first phase of five years of the UTRE research program has been completed in May 2009 and it has been successfully extended to the second phase for another four years in 2009. In the past a few years, various fundamental rock dynamics research has been conducted under the UTRE research program. It include rock dynamic testing and modelling, rock joint dynamic testing and modelling, development of discontinuous deformation analysis methods, analysis of stress wave propagation in jointed rock mass, and scaled and field blast tests, etc. The present paper mainly updates the results related to rock and rock joint dynamic properties, numerical modelling of rock mass, stress wave propagation in jointed rock mass, theoretical derivation of underground explosion induced ground motion. In the rock and rock joint dynamic properties part, we mainly tested the dynamic properties of granite rock specimen which were collected from the Bukit Timah formation covering about one-third on the Singapore geological map. Dynamic uniaxial/triaxial compression, shear and tensile splitting tests have been carried out to the granite specimen. Artificial joints using dry and saturated sand or clay layers have also been tested by using modified split Hopkinson pressure bars made by granite cores. In the numerical modeling of rock mass deformation, the numerical manifold method is adopted and it has been successfully extended to a three dimensional version.

Abstract The behavior of joints and intact rock is characterized by some parameters which have interactive effects on rock mass problems. Moreover, some of these parameters are not easily measured and they may be variable in the region of the problem. Joint normal and shear stiffness are the mechanical parameters which can be assessed in distinct element modeling. Knowing that the strength conditions of discontinuities are determined by the stress distribution through the model and along discontinuities, this paper is concerned on the effect of selected stiffness values on Distinct Element Method (DEM) computed stresses in the rock masses. 1. Introduction Development of distinct element method (DEM) has been a significant step to identify the behavior of fractured rock masses. The behavior of joints and intact rock is defined by some parameters which have interactive effects on problems. Some of these parameters are not easily measured and furthermore may be variable in the region of the problem. Thus it is momentous to recognize the influence of variation of these parameters and their interactive effects on reliability of modeling results. Joint normal and shear stiffness are the mechanical parameters which can be evaluated by distinct element modeling. It sounds to be essential to know the effects of selected stiffness values on the obtained results. 2. Estimation of Joint Stiffness Joint stiffness is not an easily measured or well known parameter. Methods of estimating joint stiffness have been derived. Two possible methods are presented here. One is based on the deformation properties of the rock mass and the intact rock; the other is adopted from the properties of the joint infilling material. 2.1. Stiffness estimated from rock mass properties Approximate stiffness values can be backcalculated from information on the deformability and joint structure in the jointed rock mass and the deformability of the intact rock. If the jointed rock mass is assumed to have the same deformational response as an equivalent elastic continuum, then relations can be derived between jointed rock properties and equivalent continuum properties. For uniaxial loaded rock containing a single set of uniformly spaced joints oriented normal to the direction of loading, the following relation applies. 2.2. Stiffness estimated from joint infill properties Another approach for estimating joint stiffness assumes that a joint has an infill material with known elastic properties. The stiffness of a joint can be evaluated from the thickness and modulus of the infilling material by the following equations. 3. Empirical Relation of Joint StiffnessValues Values for normal and shear stiffness of rock joints typically can range from roughly 10 to 100 MPa/m (for joints with soft clay infilling), to over 100 GPa/m (for tight joints in granite and basalt). Published data on stiffness properties for rock joints are limited; summaries of data can be found in Kulhawy [5], Rosso [6] and Bandis et al. [7].

ABSTRACT Today, grouting is used as an aid in ground improvement in most civil and mining projects. Groutability and grout penetration depth are subjects that are considered in grouting operation. As discontinuities compose the main paths for fluid flow in jointed rock mass, geometric characteristics, such as joint aperture, spacing and orientation, affect the grout flow. On the other hand, fluid flow in joint is a hydromechanical process and the state of applied stress on joint affects the fluid flow. Knowledge of these parameters has advantages in prediction of grouting results (grout penetration and intake). Unlike water (Newtonian fluid), stable cement-based grout usually acts as a Bingham fluid. In this study the effect of important joint geometric characteristics on grout intake and penetration depth was simulated hydromechanically using the UDEC code. The gained results show that grout intake and penetration depth increase as joint aperture and normal stiffness increase and in-situ stress decreases. Increase in joint spacing does not have any effect on penetration depth but decreases the grout intake. The effect of joint orientation on grouting process is strongly dependent on in-situ stress state. 1. Introduction Presence of fractures in rock mass decreases the rock mass strength and stiffness and increases its permeability. Grouting is one of the commonly adopted methods that are used to improve the rock mass quality. Groutability and grout penetration depth are two main factors for design of grouting operations. Several parameters affect the groutability and grout penetration depth. Knowledge of these parameters is technically and economically useful for optimum design of grouting. Since, the permeability of intact rock, as compared to joints, is very low, the discontinuities are main paths for grout flow in jointed rock mass. Accordingly, the joint characteristics including aperture, spacing and orientation influence the grout flow and grout intake and penetration depth. Moreover, various fluids have different flow behaviour (i.e. rheology). Unlike water, which behaves as a Newtonian fluid, cement-based grout is a non-Newtonian fluid. Bingham fluid model is the most appropriate model for cement based grouts. Based on Bingham fluid model, the effect of joint geometric characteristics was investigated analytically and numerically by many researchers, [1, 2, 3, 4, 5]. In most of these studies, grout flow was modeled only hydraulically, while fluid flow in joints is a hydromechanical process and the state of applied stress on joint also affects the fluid flow. In this study the effect of important joint geometric characteristics on grouting process was simulated hydromechanically. 2. Theoretical basis of grout flow injoints Rheological models are used to characterize the fluid flow and deformation. These models describe the relation between shear stress and strain rate of fluid. Fluids are either Newtonian or non-Newtonian, rheologically. In Newtonian fluids, relation between shear stress and shear strain rate is linear (Fig1).

ABSTRACT In this paper a new formulation of the stiffness matrix for a joint element in element free Galerkin method (EFGM) is presented. The meshless methods are new techniques in numerical analysis, particularly on rock mechanics. These methods are suitable for calculation of large deformation happened in rock mechanics. New formulations of the stiffness matrix for a joint element in element free Galerkin method; as one of meshless methods, is presented in this paper. This formulation was performed in local coordinate system and also was used to model rock joints and soil-soil and soil-structure interfaces. Moreover the formulation is presented for both elastic and elastoplastic state. The new solution of the joint stiffness matrix was obtained in this research and also it was observed that this method can be easily used in an EFG code. The results show good agreement between EFGM calculation and finite difference method. 1. Introduction The joint element was originally developed by Goodman et al. [1] in plane strain and plane stress state. They analyzed, jointed rock mass that it has been applied to soil-structure and rockstructure interaction studies. Subsequently, it was determined that to more accurately model the behavior of geological structures. Zienkiewicz et al. [2] presented the use of continuous isoparametric elements with a simple nonlinear material property for shear and normal stresses, assuming uniform strain in the thickness direction. Ghaboussi et al. [3] presented an axisymmetric slip surface element, which they reported to be singular under certain conditions. For a continuous mortar joint of thickness e obeying to a Masars damage law [4], defined by a Young modulus E, a Poisson coefficient υ and a damage threshold εdo. Faruque [5] presented an axisymmetric interface element that involves an iterative scheme to obtain convergence. Factors affecting this rate convergence were also discussed. The sand-structure interface developed by Zeghal and Edil [6]. They were modeled based on physical observations and surface of slippage was idealized to be sinusoidal based on an intensive numerical simulation program. Wang et al.[7] a constitutive model based on limit concept is proposed to predict the behavior of rock interfaces and joints. 2. EFG Method The moving least squares approximation was developed by Lancaster and Salkauskas [8] for data fitting and surface construction. Nayroles et al. [9] has used MLS to construct shape function and named it diffuse element method (DEM). DEM was modified by Belytschko [10] and who named it the element free Galerkin method.

ABSTRACT: Based on equivalent energy theory, the anisotropy damage constitutive model of jointed rock mass is set up with joint surface closing and friction considered, the flexibility tensor and its increments are deduced. The model is applied to analyze the stability of permanent high ship-lock slopes of Three Gorges, and the numerical results show that the model is fit for simulating damage evolution and progressive failure of surrounding rock mass of the project during excavation and support. I. INTRODUCTION Joints not only have effect on mechanical properties and distribution of stress in rock mass, but also influence seepage trajectory and failure modes of rock mass. Damage evolution of joints depends on loading history and distribution of joints. Many simplified mechanical model have been set up to study mechanical properties of rock mass (Budiansky & O'Connell(1976), law & Broekenbrough (1987), Fanella & Krajoinovic (1988), Hudson (1983), Oda (1982)). But in these achievements, the influence of joint closing and joint surface friction still haven't been taken into consideration. In this paper, the anisotropy damage constitutive model is established with joint surface closing and joint friction considered. 3. APPLICATION IN THREE GORGES The new established mechanical model of rock mass is applied to analyze the stability of surrounding rock mass of high ship lock slopes of Three Gorges. The rock mass at the flight lock area consists of amphibole plagioclase granites of ante Sinian System. The axial direction of the lock chamber segment of the permanent flight lock is 110"58' 08". Because some joint sets cross the lock chamber axis with a large angle. Only two joint sets with strike of NE-NEE(B) and NWW(A) are taken into consideration. The two sets have an average joint spacing of 1.2m and 1.85m respectively. The mechanical properties of the two sets are shown in table 2. 3. 1 In situ stress It is considered that initial horizontal stress is generally very low in the shallow and soft stratum because of stress relaxation effect, which is verified by in situ monitoring. Therefore, the initial stress in the completely, intensively weathered stratum is taken as that caused only by the dead weight. 3.2 Anchoring indexes Three kinds of anchoring method are designed in the slopes: systematic bolts, prestressed bolts and prestressed cables. The anchoring parameters are shown in table 3. 4. CONCLUSION New mechanical model with joint closing and friction considered is applied to analyze the stability of high ship lock slopes in three Gorges, and leads to some useful conclusion: The new established model is fit for analysis stability and damage evolution of joints in hard rock during excavation and support. With two joint sets considered in numerical simulation, the results show that some joints around excavation boundary are propagated. In general meaning, surrounding rock mass of ship lock slopes are stable. REFERENCES Budiansky 8, O'Connel R. J. Elastic moduli of a cracked solid. Int. J. Solids structures. 1976,12(2):81–97.

ABSTRACT: Adopted damage mechanics, constitutive relation and damage evolution equation of jointed rockmass are presented and used to evaluate the deformation behavior and stability of jointed rockmass. The application to engineering shows that the model presented is reasonable and practical. I. INTRODUCTION A great number of engineering practices have indicated that the failures of rockmass are mostly because of the evolution of internal deficiency such as joints and cracks, so it's quite necessary to study the weaken and damage-evolution effects of such joints and cracks in rockmass. Commonly we use anchor to reinforce rock mass and restrict its deformation and failure. To study the deformation character of such anchored rockmass, we have to establish an effective model, which can describe the reinforcement effect of the anchor in jointed rockmass. In this paper, a constitutive model and damage evolution equation of joint-crack rockmass is established, and a kind of anchored- damage rock clement is devised to evaluate the stability and deformation of the rockmass. At last, an engineering application of stability analysis in an underground workhouse is presented. 2. COMPUTATION MODEL 2.1 3D damage constitutive equations for multi-crack rockmass Assuming that there are M groups of generalized joints. 3. SUPORTING MODEL OF COLUMN ELEMENT IN DAMAGED ROCKMASS WITII BOLTS After being added into rockmass, anchor and its surrounding jointed rockmass form a kind of anchor-damage column element (see Fig.1), it is built in jointed rockmass, and formulated column element of damage rockmass with bolts (CEDRB). In order to describe restricting effect of the bolt on deformation of surrounding rockmass, the stiffness of CEDRB will be added into the stiffness matrix of jointed rockmass elements in computing process. Assuming that CEDRB is a kind of orthography damaged medium and on the basis of energy equivalent theory. 4. ENGINEERING CONDITIONS AND CALCULATING PARAMETERS 4.1 Engineering Conditions Considering main workhouse of a power station, the upper span of its anchored rock beam is 3 1.60m, the bottom span is 30.00m. The maxim height of its excavated sidewall is 88.62m, and the upper sidewall's height of draft tube is 58.12m, the total length of this power station is 352.60m, where the underground workhouse part is 280.60m. The ground elevation of underground main workhouse is generally 190–200m and the bedrock is mainly composed of amphibole plagioclase granite and anorthosile enclosure. There are three sets of faults in the area of workhouse: NNN, NE and NEE-EW, among which the NNW fault angle with middle line of workhouse greater than 50°, the other two faults are poorly cementation, comprising with some substance, locally with soil. Fissures in workhouse area are fully developed, mainly composed of steep dip fissures, which takes a fraction of 61.5% of all fissures, and moderate dip fissures take 24.7%, low dip fissures take 13.7%. Surrounding rock are slightly fresh rock, mainly belongs to I, II block type. 4.2 Calculating range and parameters The calculating range of main workhouse includes No.2, 3, 4, 5, and 6 of machine units.

ABSTRACT: This paper presents results of an investigation which was carried out in order to analyze the stability of two tunnels. The tunnels were excavated in jointed rock masses of Jahrom formation. Due to structural feature and geology of the area the distinct element method was used to analyze the stability of tunnels. The code utilized according to this method was UDEC. The results gained from the numerical analysis show that the tunnel with smaller span, no major block fall occurs and hence a thin layer of shotcrete stabilizes the tunnel. However block falls and larger displacements were evident in the tunnel with larger span. The stability of the latter tunnel is achieved by using rock bolts in the sidewalls and a thin layer of shotcrete in the roof and sidewalls. I. INTRODUCTION When an underground structure is excavated in jointed rock masses, instability occurs as a result of roof fall or wall failures. The presence of discontinuities such as faults, joints and bedding planes in the rock mass dominates the response or jointed rock masses to loading. Hence the stability analysis of underground structures being driven in jointed rock mass differs greatly from those of intact rock. Numerical modeling in rock mechanics has developed significantly in recent years (Pande1990). There are various numerical methods available whichever has its own applicabilities regarding the rock mass and discontinuities encountered in underground structures. One of these methods is the distinct element method which as been developed for deformation and stability analysis of multiply jointed rock masses around underground structures. The two dimensional distinct element computer code was used to analyze the stability or tunnels being driven in jointed rack masses of Jahrom formation. 2. GEOLOGIC CONDITIONS The tunnels are driven in the jointed rock masses of Jahrom formation which is situated south west of Zagross mountains in Iran. The main rocks encountered in this formation are Limestone, marly limestone and dolomitic limestone. The rock mass surrounding the tunnels are divided into two parts: part A(50 meters in thickness) consisting of marly limestone and part B (220m in thickness) consisting of limestone and dolomitic limestone. Field investigations were carried out and the data were then analyzed by the Dips soil ware. The analyzed data show that here are two joint sets and a bedding plane in the area. Table I sows the dip and dip directions of these joint sets. 4. UNIVERSAL DISTINCT ELEMENT CODE (UDEC) The Universal Distinct Element Code (UDEC, Itasca 1992) is a numerical program where the rock mass is presented as an assemblage of distinct blocks having joints between blocks. Each block can be modeled as either rigid or deformable materials. The rigid blocks represents the medium as a set of distinct blocks which do not change their geometry as a result of applied loading. Deformable blocks are internally discretized into finite difference elements, whichever element behaves according to a prescribed linear or non-linear stress-strain constitutive relationship.