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Slope instability is a complex geological phenomenon triggered by heavy rainfall, earthquakes, tectonic forces and anthropogenic activities. Unplanned excavation of rock slopes for the development and maintenance of infrastructure such as highways, railways, and buildings in hilly regions plays a significant role in causing slope instability. The present work conducts a comprehensive stability assessment of rock slopes along the national highway (NH-44) section of the Ramban district of Jammu and Kashmir. The kinematic investigation was carried out to determine the different modes of failure of road-cut slopes, and two main modes were found: planar and wedge. Various empirical classifications have been applied for the assessment of slope stability, like geological strength index (GSI), slope mass rating (SMR), Chinese slope mass rating (CSMR), and continuous slope mass rating (CoSMR). Numerical analysis through universal distinct element code (UDEC) has been conducted to evaluate the stability of four critical rock slopes under static and dynamic loading conditions. Modelling results have provided insights into the failure mechanism, and based on these findings, remedial measures have been proposed. Three (L-1, L-3, and L-13) out of four slopes were determined to be unstable under static conditions, with factors of safety (FoS) < 1.2 and under dynamic conditions, two slopes were unstable with FoS < 1.0. However, one (L-8) slope was found to be stable under both static and dynamic conditions, with FoS 1.29 and 1.12, respectively. Installing rock bolts reduced displacement for slopes L-1 and L-13, with reductions of 11.86% and 21.05% under static conditions and 4.09% and 18.75% under dynamic conditions, respectively, while L-3 does not stabilise even after installation of rock bolts. [ABSTRACT FROM AUTHOR]

Rock anchors, which can withstand substantial forces and are essential for securing the foundations of the built environment, can fail due to steel tensile failure, bond detachment, or rock mass fracturing through uplift. In this study, uplift failure of the rock mass surrounding rock anchors was simulated using both physical and numerical models. The physical models used a specially designed testing rig with predefined sizes and different joint layouts to simulate rock mass uplift failure. The numerical models were calibrated using the physical models and used to investigate scenarios involving increased complexity and greater depths. This paper presents the load distribution within rock masses with orthogonal joints when exposed to an anchor load. Extensive analysis of the numerical models revealed that symmetrical load arches were induced in rock masses that contained a joint set oriented parallel to the loading direction. However, joints that were obliquely oriented relative to the anchor axis induced asymmetrical load arching. The greatest displacement occurred in the direction parallel to the joint set with the smallest angle to the anchor loading axis. Large-scale models with zero or near-zero in situ horizontal stress revealed that the load capacity in a rock mass with continuous vertical joints was relatively low, especially when compared to rock masses with discontinuous vertical joints. It was observed that the uplift capacity of the rock mass around an anchor decreased if the load arches of adjacent anchors overlapped; consequently, a decrease in anchor spacing was found to correspond to a decrease in uplift capacity. Highlights: Symmetrical load arches are induced within a rock mass if the joint sets are oriented parallel to or close to parallel to the anchor axis. An oblique orientation of the joints relative to the anchor axis results in asymmetrical load arching in the rock mass when the anchor is loaded. Rock masses with continuous vertical joints have a low load capacity, especially compared to rock masses with discontinuous vertical joints. In a row of rock anchors, the rock mass uplift capacity of individual anchors is decreased if the anchor spacing is too low. [ABSTRACT FROM AUTHOR]

Fractures generated in the overlying rock of coalfield fire areas can develop into air leakage and oxygen supply channels, thus helping sustain and intensify the fire. However, the formation, evolution, and distribution of such fractures are complex. This study used physical similarity simulation and numerical simulation to analyse the formation and evolution process of the underground coal field fire area at the Tanyaoqu coalmine. The first air leakage and oxygen supply channel in a coal fire area is formed when the overlying rock fractures reach the surface. The average collapse step distance of overlying rock after the formation of the first air leakage and oxygen supply channel in the research area was approximately two times that before. The length of the main fracture in the overlying rock increased gradually with coal combustion temperature. The angle between the main fracture and the horizontal plane decreased as temperature increased before the formation of the first channel and increased with temperature after the formation. When the coal combustion temperature was 600, 800, and 1000 °C, the distances from the coal seam damage position to the first air leakage and oxygen supply channel position are 122.7, 114.7, and 103.1 m, respectively. [ABSTRACT FROM AUTHOR]

Uniaxial compression tests on Hydro-StoneTB® porous cubes were numerically modeled using a distinct element program (UDEC) for two-dimensional geological material simulation. Under uniaxial compression, numerical square models with varying void porosity and geometry, identical to an experimental testing, were simulated. The open-ended longitudinal openings in the experimental specimens, cubic porous Hydro-StoneTB®, were of various forms, sizes, uniformity, and distributions. UDEC's Voronoi tessellation joint generator was used to simulate the material of the experimental specimens as an assembly of discrete units interacting along their boundaries. The results showed that the numerical results from the two-dimensional numerical analysis utilizing the discrete element method, UDEC program, were consistent with the experimental data. However, when compared to the experimental values, the numerical analysis produced conservative values for both uniaxial compressive strength and Young's modulus due to the modeling of a three-dimensional material in a two-dimensional planar strain. Furthermore, regardless of void porosity or geometry, the tension (axial splitting) failure mode is the dominating failure mode of rock-like materials including voids, similar to the experimental results. It was also demonstrated that using a power relationship, two-dimensional numerical data can be converted to three-dimensional experimental results. [ABSTRACT FROM AUTHOR]

The assessment of yielding rockbolt performance during rockbursts with actual seismic loading is essential for rockburst supporting designs. In this paper, two types of yielding rockbolts (D-bolt and Roofex) and the fully resin-grouted rebar bolt are modeled via the "rockbolt" element in universal distinct element code (UDEC) after an exact calibration procedure. A two-dimensional (2D) model of a deep tunnel is built to fully evaluate the performance (e.g., capacity of energy-absorption and control of rock damage) of yielding and traditional rockbolts based on the simulated rockbursts. The influence of different rockburst magnitudes is also studied. The results suggest that the D-bolt can effectively control and mitigate rockburst damage during a weak rockburst because of its high strength and deformation capacity. The Roofex is too "soft" or "smooth" to limit the movement of ejected rocks and restrain the large deformation, although it has an excellent deformation capacity. The resin-grouted rebar bolt can maintain a high axial force level during rockbursts but is easy to break during dynamic shocks, which fails to control rapid rock bulking or ejection. Three types of rockbolts cannot control the large deformation and mitigate rockburst damage effectively during violent rockbursts. The rockburst damage severity can be significantly reduced by additional support with cable bolts. This study highlights the effectiveness of numerical modeling methods in assessing the complex performance of yielding rockbolts during rockbursts, which can provide some references to improve and optimize the design of rock supporting in burst-prone grounds. [ABSTRACT FROM AUTHOR]

The deterioration of rock mass in the hydro-fluctuation belt and reservoir-induced earthquakes in the Three Gorges Reservoir Area (TGRA) have great impact on the stability of bedding rock slope. The cumulative damage mechanism and stability of bedding rock slope under the deterioration of rock mass in the hydro-fluctuation belt, when subjected to repeated seismic loads, were investigated using the shaking table model test and Universal Distinct Element Code (UDEC) numerical simulation. Under the continuous action of seismic loads, the peak ground acceleration (PGA) amplification coefficient clearly weakens; the cumulative displacement, pore water pressure and earth pressure of the slope show a change trend of increase, increase and decrease, respectively; the damping ratio and damage degree (DG) of the slope increase, while the natural frequency of the slope decreases gradually; the nonlinear cumulative damage mechanical models of the slope in the stages of microseism—small earthquake action and strong earthquake action can be characterized by the cubic function of “S-type” and the exponential function of “steep rise type,” respectively. Based on the good agreement between the experimental observations and numerical simulation results, the evolution process of the dynamic cumulative damage—instability and typical failure modes of the slope (including the hydro-fluctuation belt) was observed. Furthermore, the stability of the slope increases with the decrease of the slope height (A), slope angle (B), seismic load amplitude (C), seismic load frequency (D), or deterioration depth of rock mass in hydro-fluctuation belt (E), while it decreases with the increases of the strength degradation ratio of the rock discontinuities in hydro-fluctuation belt (F); the ranking of sensitivity of the mentioned-above influence factors is C > A > D > E > B > F according to the orthogonal analysis method (OAM). [ABSTRACT FROM AUTHOR]

In this work, the thermo-mechanical stress–strain history of an Alpine slope is analyzed, with particular focus on the historical Cimaganda large landslide (Sondrio Province, Italy), which mobilized an estimated volume of 7.5 mm3 of rock material. Accurate geomorphological and geomechanical characterization involving field surveys and laboratory testing was carried out, leading to the development of a conceptual model of the slope. A thermo-mechanical semi-coupled approach was developed, considering both glacial debuttressing and thermo-mechanical effects due to gradual exposure of the slope to atmospheric conditions and paleo-temperature redistribution resulting from the Last Glacial Maximum deglaciation. A 2D distinct-element numerical approach was adopted, supported by a 2D finite-element analysis to simulate heat diffusion over the Valley cross-section. Modelling results allow to simulate the general evolution of the Cimaganda rock-slope and to highlight the significance of thermal processes in preparing rock-slope instabilities. While the mechanical effect of ice thickness reduction alone brings about moderate rock mass damage, the introduction of temperature couplings results in a substantial increase of damage, representing a significant factor controlling the stress–strain evolution of the slope. Simulated displacement and the development of a deep region of shear strain localization at a depth roughly corresponding to that of the detected Cimaganda sliding surface, allow to highlight the significance of temperature influence in preparing the rock-slope to instability. Highlights : The effects of surface temperature variations on the stress-strain evolution of an Alpine rock-slope are examined through numerical simulation. This study contributes to the understanding of Thermo-Mechanical processes driving damage in rock masses. Results showed how Thermo-Mechanical stresses induced by temperature variations at both long- and short-term timescales, can represent a significant preparatory factor to rock slope instability. The factors introduced in the analysis allowed to simulate the general evolution of the Cimaganda rock-slope, which is corroborated by field survey data. [ABSTRACT FROM AUTHOR]

Block-flexure is the commonest mode of toppling failure and can be frequently encountered in anti-inclined rock slopes. In this work, the failure mechanism of block–flexure toppling (BFT) was investigated using centrifugal and numerical models. The numerical model was configured using the Universal Distinct Element Code (UDEC) and calibrated with the results of the centrifuge test. All the simulation results, including the measured displacements, failure load, and failure surface, are generally in line with that of experimental results. Further, the results of simulations show that, well before the appearance of instability in the jointed rock slope, slipping failure and opening fractures had occurred in the interlayer. Moreover, all the acting points of normal forces in steep joints are located between the bottoms and the midpoints of the columns under consideration, in the process of toppling failure. Finally, sensitivity of joint parameters, including the connectivity rate of discontinuous cross-joints, the thickness of the rock column joint, joint friction angle, and joint cohesion, were performed to investigate the effects of the tensile strength of intact rock. The results indicate that joint cohesion and thickness of the rock column greatly influence the failure load (represents safety factor of the slope). The connectivity rates of the discontinuous cross-joints and joint friction angle were found to have significant effects on the shape and location of the basal failure plane. This research would provide a deep understanding on the failure mechanism of BFT for relevant scholars. [ABSTRACT FROM AUTHOR]

Uncertainty in input fracture geometric parameters during analysis of the stability of jointed rock slopes is inevitable and therefore the stochastic discrete fracture network (DFN) — distinct element method (DEM) is an efficient modeling tool. In this research, potentially unstable conditions are detected in the right abutment of the Karun 4 dam and downstream of the dam body as a case study. Two extreme states with small and relatively large block sizes are selected and a series of numerical DEM models are generated using a number of validated DFN models. Stability of the rock slope is assessed in both static and dynamic loading states. Based on the design basis earthquake (DBE) and maximum credible earthquake (MCE) expected in the dam site, histories of seismic waves are applied to analyze the stability of the slope in dynamic earthquake conditions. The results indicate that a MCE is likely to trigger sliding of rock blocks on the rock slope major joint. Furthermore, the dynamic analysis also shows a local block failure by the DBE, which can consequently lead to slope instability over the long term. According to the seismic behavior of the two models, larger blocks are prone to greater instability and are less safe against earthquakes. [ABSTRACT FROM AUTHOR]

A series of DEM-FDM coupled numerical simulations were performed to study the failure process of the isolated stone column in soft soil according to the Universal Distinct Element Code. In the proposed numerical model, the stone column was represented by a rigid blocky system based on the Voronoi tessellation; the surrounding soil was represented as the continuum Mohr-Coulomb material. The settlement, bulging deformation, and failure processes were tracked during the complete loading process, which enables the column-soil interactions to be observed visually. The deformation process and corresponding failure modes of isolated stone columns embodied in soft soil are graphically illustrated according to the numerical analysis. The traditional ultimate bearing capacity prediction formulas for the isolated stone column cannot be directly used for the local shear failure mode. The soil stiffness should be the critical parameter to calculate the lateral confining stress rather than the soil shear strength. [ABSTRACT FROM AUTHOR]

Laboratory tests showed that the average direct tension strength (DTS0) of the Lac du Bonnet granite was 6.9 MPa, and significantly less than its average Brazilian tension strength (BTS0), i.e., 8.8 MPa. In this paper, a grain-based model (GBM) with a 2D universal discrete element code (UDEC) was used to explore factors that could control the difference in the direct tension strength (DTS) and Brazilian tension strength (BTS) of the Lac du Bonnet granite from the micromechanical point of view. Micro parameters of the grain contacts were investigated, i.e., the tensile strength (T), cohesion (c), friction angle (φ), and the ratio of the shear to normal stiffness (λ). Results show that both BTS and DTS highly depended on log(λ). With an increase in log(λ), the BTS first increased nonlinearly and decreased instead after achieving a peak while the DTS always increased nonlinearly. The BTS was sensitive to T and c, while the DTS was mainly sensitive to T. The ratio of DTS to BTS first decreased with the increase of log(λ) and then increased instead from a minimum. It was found that the GBM with UDEC can well reproduce the uniaxial compression, direct tension and Brazilian tests of the Lac du Bonnet granite simultaneously only on condition that λ = 2.51. This indicated that the shear stiffness of the grain boundary in the Lac du Bonnet granite may be several times larger than its normal stiffness. This may be the main factor controlling the difference in the BTS and DTS of the Lac du Bonnet granite. [ABSTRACT FROM AUTHOR]

Micro-discrete fracture networks (μDFNs) have been integrated into grain-based models (GBMs) within the numerical software UDEC to assess rock block strength through a series of unconfined compressive strength (UCS) tests of progressively larger in size numerical specimens. GBMs were generated by utilizing a Voronoi tessellation scheme to capture the crack evolution processes within the intact rock material, and μDFNs were separately created and embedded into the GBMs to simulate the effect of pre-existing defects. Various μDFNs realisations were generated stochastically within the software FracMan to assess the combined impact of defect intensity, persistence, strength and specimen size. The resulting synthetic rock block models were used to assess the "flawed" material strength at block scale through a rigorous sensitivity numerical analysis. The acquired results predict a progressive strength reduction with decreasing intact rock quality and certain trends are captured when rock block strength is expressed as a function of a newly proposed "Defect Intensity× Persistence" factor. This allow us to standardise the data along specific strength reduction envelopes and to propose generic relationships that cover a wide range of defect geometrical combinations, defect strengths and sample sizes. Accordingly, an attempt is undertaken to refine two existing empirical approaches that consider the effect of scale and micro-defects explicitly for predicting the UCS of rock blocks. [ABSTRACT FROM AUTHOR]

Landslide is a natural hazard which carries water, mud, debris and sometimes large boulders. Earthquakes, heavy rainfall and tectonic forces are natural responsible factors for landslides, whereas overpopulation and rapid development in the hilly region are unnatural factors which involve human activities such as construction/maintenance of roads, highways, railways and buildings by the unplanned excavation of rock slopes. Both natural and unnatural factors have been accountable for the increase in the probability of landslides in the past few decades. In the present study, stability analysis of rock slopes has been carried out along Kulikawn to Saikhamakawn road section of Aizawl. Kinematic analysis has been performed to identify the road cut slopes which have the potential to fail, and mainly two types of failures were found, i.e., wedge and topple failure. In order to check the stability of road cut slopes, Geological Strength Index, slope mass rating (SMR) and continuous slope mass rating (CoSMR) have been used in this study. Numerical modelling has also been performed to assess the stability of the road cut slope. The maximum displacement of 0.79 m with a maximum velocity of 0.78 m/s has been found for rock slope at location L1 using numerical modelling which confirms the finding from kinematic analysis, SMR and CoSMR analysis. [ABSTRACT FROM AUTHOR]

The Hoek–Brown (HB) failure criterion is one of the most widely used failure criteria in rock engineering. Based on the Geological Strength Index (GSI) system, a number of empirical models have been proposed in parallel with this criterion to estimate the strength and deformation properties of rock masses such as uniaxial compressive strength (UCS) and deformation modulus. However, the GSI system does not incorporate the effects of joint orientation β on the quality of a rock mass. This means that these empirical models cannot capture anisotropic rock mass strength caused by joint orientations. In this research, UDEC rock mass models, which are calibrated by laboratory data, are used to investigate the effects of joint orientation on rock mass strength in an unconfined state. The values of UCS obtained from the numerical simulation are then compared with those calculated from traditional empirical UCS models based on the GSI system. The comparison study shows that the value of UCS is significantly overestimated by the traditional empirical model when 10° < β < 45°, which will have serious safety implications for engineering designs. To rectify the problem, based on the analysis of numerical simulation results, an anisotropic weighting factor fβ is proposed to be used to refine the empirical UCS model. The modified UCS model is demonstrated to be capable of giving conservative but more accurate prediction of the rock mass strength for various joint orientations, which will result in more optimal and safer engineering designs. [ABSTRACT FROM AUTHOR]

Toppling is a mode of failure that may occur in a wide range of layered rock strata in rock slopes. According to the results of physical model tests and field investigations of anti-inclined rock slopes, most real instabilities are of the sliding or flexural-toppling type. Failure often initiates at the slope toe, and the failure surface is usually multi-planar rather than planar. These properties should determined by searching rather than based on assumption. Taking these problems into account, in this paper we propose a theoretical model for rock slopes with a potential for sliding or flexural-toppling failure on the basis of two physical model tests. An innovative approach for the stability analysis of such slopes based on the limit equilibrium theory is then proposed. Subsequently, a comparative analysis is carried out using the discrete element method and the Aydan et al. method with the aim to verify the validity and accuracy of the proposed approach. Finally, the possible difference between angles of the basal calculation plane and the failure surface of the sliding zone and superimposed toppling zone with respect to the plane normal to the discontinuities is presented. [ABSTRACT FROM AUTHOR]

The stability of the left-bank slope is a crucial geological engineering problem at the Baihetan hydropower station, China. Due to continuous excavations on the rock slope, different regions of the surrounding rock mass undergo varying degrees of unloading deformation. It is important to assess the stability of the rock slope from a macroscopic viewpoint by investigating its deformation characteristics and mechanisms. Therefore, in this work, microseismic (MS) monitoring was first employed to detect the progressive rock mass damage in the rock slope subjected to excavation, including the initiation, propagation, coalescence, and interaction of rock microfractures. Numerical modeling was subsequently performed to understand the deformation and failure mechanism of the rock slope. Moreover, traditional surveying approaches (i.e., multiple-point extensometers and inclinometers) and field observations were also used to analyze the deformation and failure characteristics of the rock slope. The MS monitoring results showed that spatiotemporal regularities in the evolution of seismic source locations were indicators of deformation failure and potential sliding surfaces. MS event clustering can be used to delineate activated pre-existing geological structures (i.e., LS331 and LS337). The simulation results show that the deformation and failure characteristics of the rock slope are mainly controlled by pre-existing weak structural planes (i.e., the intraformational faulted zones LS3319, LS331, and LS337 and fault F17). These results agree well with the results of geological data and conventional monitoring data. Our study reveals that an integrated approach combining MS monitoring, numerical modeling, traditional surveying, and field observations leads to a better understanding of the behavior of the rock slope under the influence of excavation as well as greater control of the working faces, ensuring safety under complex geological and excavation conditions. [ABSTRACT FROM AUTHOR]

A series of simplified approaches are evaluated for their effectiveness to estimate the seismic vulnerability of historical masonry towers. First, collapse loads are evaluated on sixteen “idealized” benchmark cases with different slenderness and shear area. Both analytical and computational approaches are used, namely the analytical procedure proposed by the Italian Guidelines on the Built Heritage and pushover analyses conducted using the commercial codes UDEC and 3Muri. The sixteen towers are representative cases which can be encountered in practice. Their geometry is idealized into parallelepiped blocks with hollow square cross-sections, thus favoring the utilization of 2D approaches, beneficial to drastically reduce the effort required for repeated computations. In addition, a Monte Carlo MC upper bound limit analysis strategy is proposed, in order to have an insight into the possible failure mechanisms for the different cases investigated. Deliberately is avoided the introduction of any form of irregularity and they are supposed isolated from the neighboring buildings, to obtain results exclusively dependent from geometric features. Among all the possible collapse mechanisms, five of them are selected according to the probability of occurrence based on past earthquake experiences. Five million cloud points of collapse accelerations are obtained by carrying the height, slenderness and shear area of the idealized towers. The approach is very fast and allows identifying different regions where single mechanisms are active. The results are confirmed repeating MC simulations with a triangular FE upper bound limit analysis discretization of the idealized towers. A series of equations are provided in order to assist engineers and practitioners to obtain a preliminary estimation of their expected collapse acceleration. For validation purposes, the results obtained previously with refined full 3D FE models of 25 towers located in the Northern Italy are reported. Satisfactory agreement between the predictions provided by simplified methods and sophisticated analyses are obtained. [ABSTRACT FROM AUTHOR]

Wangxia rock mass was situated in Three Gorges around Yangtze River and considered to be one of largest unstable rock mass in China. The present study aims to investigate the damage of Wangxia rock mass and protect the lives of people and shipping from rockfall phenomenon. Mohr-Coulomb model in Universal Distinct Element Code was built to find out the rockfall initiation position. RocFall 4.0 program has been used to calculate horizontal location of rock end-points, maximum bounce heights, total kinetic energy, and translational velocities of the falling blocks of different weights and the input parameters were obtained by back analysis. The results show that the maximum value of bounce height and total kinetic energy is 3.63 m and 2819 kJ respectively at the horizontal location of 152.4 m, where proper protection measures should be adopted to minimize the risk of the damage of the Wangxia rock mass. Finally, the results of simulation indicate that a barrier of 5 m height and 3000 kJ absorption capacity is enough to resist the falling stones. [ABSTRACT FROM AUTHOR]

The transmission of seismic waves in a particular region may influence the hydraulic properties of a rock mass, including permeability, which is one of the most important. To determine the effect of a seismic wave on the hydraulic behavior of a fractured rock mass, systematic numerical modeling was conducted. A number of discrete fracture network (DFN) models with a size of 20 m × 20 m were used as geometrical bases, and a discrete element method (DEM) was employed as a numerical simulation tool. Three different boundary conditions without (Type I) and with static (Type II) and dynamic (Type III) loading were performed on the models, and then their permeability was calculated. The results showed that permeability in Type III models was respectively 62.7% and 44.2% higher than in Type I and Type II models. This study indicates that seismic waves can affect deep earth, and, according to the results, seismic waves increase the permeability and change the flow rate patterns in a fractured rock mass. [ABSTRACT FROM AUTHOR]

This paper presents a numerical simulation of S-wave propagation across a rough, filled discontinuity using the universal distinct element code (UDEC). The ability of UDEC to simulate a stress wave across a smooth and planar discontinuity filled with an elastic material is validated through comparisons with analytical solutions. Next, the effect of the plastic deformation of the fill on the wave propagation is investigated. The model is extended to further study S-wave propagation across a filled discontinuity with rough interfaces, which is described using a sawtooth. The transmission coefficient defined by the energy is used to measure the wave attenuation. Finally, a parametric study is conducted to investigate the influences of the filled thickness, asperity angle, and incident amplitude on the transmission waves and transmission coefficients. The asperity angle and filled thickness together determine the transmitted waveform and transmission coefficient. The transmitted wave may be cut off when the incident wave amplitude exceeds a threshold value. The transmission coefficient decreases with a different trend with the incident wave amplitude increasing when the asperity angle varies. Compared with planar discontinuity, a filled discontinuity with rough interfaces is more sensitive to the amplitude of the incident wave. The causes of these phenomena are analyzed in detail. In addition, the deformation of the fill material is strongly related to the wave attenuation. [ABSTRACT FROM AUTHOR]

The mechanical behavior of rock containing parallel non-persistent joint sets was studied using a numerical model. The numerical analysis was performed using the discrete element software UDEC. The use of fictitious joints allowed the inclusion of non-persistent joints in the model domain and simulating the progressive failure due to propagation of existing fractures. The material and joint mechanical parameters used in the model were obtained from experimental results. The results of the numerical model showed good agreement with the strength and failure modes observed in the laboratory. The results showed the large anisotropy in the strength resulting from variation of the joint orientation. Lower strength of the specimens was caused by the coalescence of fractures belonging to parallel joint sets. A correlation was found between geometrical parameters of the joint sets and the contribution of the joint sets strength in the global strength of the specimen. The results suggest that for the same dip angle with respect to the principal stresses; the uniaxial strength depends primarily on the joint spacing and the angle between joints tips and less on the length of the rock bridges (persistency). A relation between joint geometrical parameters was found from which the resulting failure mode can be predicted. [ABSTRACT FROM AUTHOR]

The effect of groundwater on strength and deformation behavior of fractured crystalline rocks is one of the important issues for design, performance and safety assessments of surface and subsurface rock engineering problems. However, practical difficulties make the direct in situ and laboratory measurements of these properties of fractured rocks impossible at present, since effects of complex fracture system hidden inside the rock masses cannot be accurately estimated. Therefore, numerical modeling needs to be applied. The overall objective of this paper is to deepen our understanding on the validity of the effective stress concept, and to evaluate the effects of water pressure on strength and deformation parameters. The approach adopted uses discrete element methods to simulate the coupled stress-deformation-flow processes in a fractured rock mass with model dimensions at a representative elementary volume (REV) size and realistic representation of fracture system geometry. The obtained numerical results demonstrate that water pressure has significant influence on the strength, but with minor effects on elastic deformation parameters, compared with significant influence by the lateral confining pressure. Also, the classical effective stress concept to fractured rock can be quite different with that applied in soil mechanics. Therefore, one should be cautious when applying the classical effective stress concept to fractured rock media. [ABSTRACT FROM AUTHOR]

In this study, numerical modeling of a large-scale decoupled underground explosion test with 10 tons of TNT in Älvdalen, Sweden is performed by combining DEM and FEM with codes UDEC and AUTODYN. AUTODYN is adopted to model the explosion process, blast wave generation, and its action on the explosion chamber surfaces, while UDEC modeling is focused on shock wave propagation in jointed rock masses surrounding the explosion chamber. The numerical modeling results with the hybrid AUTODYN-UDEC method are compared with empirical estimations, purely AUTODYN modeling results, and the field test data. It is found that in terms of peak particle velocity, empirical estimations are much smaller than the measured data, while purely AUTODYN modeling results are larger than the test data. The UDEC-AUTODYN numerical modeling results agree well with the test data. Therefore, the UDEC-AUTODYN method is appropriate in modeling a large-scale explosive detonation in a closed space and the following wave propagation in jointed rock masses. It should be noted that joint mechanical and spatial properties adopted in UDEC-AUTODYN modeling are determined with empirical equations and available geological data, and they may not be sufficiently accurate. [ABSTRACT FROM AUTHOR]

Numerical simulations have been performed to assess the stability of a large underground powerhouse in the Himalayas, using both finite element and distinct element approaches. Large convergences (around 250-300 mm) along the 45 m high wall of the Machine Hall have been measured by total station measurements during construction and up to 60 mm in the post construction and operational phase. Displacements are continuing at a reduced rate of about 3 to 6 mm per year. A large number of rock bolts have failed in the powerhouse and the shotcrete liner presents cracks and failure marks, thus questioning the long-term integrity and stability of the existing rock support system. The purpose of the numerical analysis was to back-calculate the prevailing rock mass conditions surrounding the machine hall, thereby gaining a better understanding of the mechanisms responsible for the instability in the cavern. The results from the analysis indicate that there was possibly an underestimation of the rock support requirements needed for the cavern, coupled with a not so good installation (incomplete grouting of the bolts). Both the length and the capacity of the rock bolts were underestimated presumably due to the existence of a high stress regime in the area, which may not have been taken into consideration in the design of rock support. The effect of a possible earthquake, frequent in this area, has also been studied and proves to induce a significant increase of the displacements and the support failure. [ABSTRACT FROM AUTHOR]

The Ajanta caves are situated in Deccan Trap basalt and declared as one of the World Heritage Sites by UNESCO. The present study aims to investigate and understand the damage of caves and to protect the life of the visitors from the rockfall phenomenon at and around the caves. Information related to the detached rock mass/block was acquired by using Barton-Bandis model in Universal Distinct Element Code. Parameters for rockfall simulation were determined by rigorous field study and laboratory experiment and then calibrated some of the parameters by back analysis. RocFall 4.0 program has been used to calculate maximum bounce heights, total kinetic energies, and translational velocities of the falling blocks of different weights. The maximum bounce height varies from 14.0 to 19.0 m for the weight of the block size ranging from 500 to 2,000 kg, whereas the maximum velocity and maximum kinetic energy are 30.0 m/s and 917.66 kJ, respectively. Finally, the results of simulation have been used to find out the position of the barrier and its capacity to design the protection barrier. The barrier capacity was found to be 325 kJ for 2,000 kg of falling blocks at a height of 50.0 m. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study on wave transmission across jointed rock masses with UDEC, where multiple intersecting joint sets exist. The capability of UDEC of studying wave transmission across rock joints is validated through comparison with analytical solutions and experimental data. Through parametric studies on wave transmission across jointed rock masses, it is found that joint mechanical and spatial parameters including joint normal and shear stiffnesses, nondimensional joint spacing, joint spacing ratio, joint intersecting angle, incident angle, and number of joint sets together determine the wave transmission. And for P wave incidence, compared with other parameters, joint normal stiffness, nondimensional joint spacing, and joint intersecting angle have more significant effects on wave transmission. The physical reasons lying behind those phenomena are explained in detail. Engineering applications and indications of the modeling results are also mentioned. [ABSTRACT FROM AUTHOR]

Although most cut slopes in Ohio consist of inter-layered, sub-horizontal units of hard and soft sedimentary rocks (sandstone, limestone, dolostone, shale, claystone, mudstone), slopes consisting of relatively thick hard rock units are not uncommon. Design of stable cut slopes in hard rock units needs to consider rock mass strength and orientation of discontinuities with respect to slope face. Results of kinematic stability analyses show that hard-rock cut slopes are less likely to have conventional plane and wedge failures, caused by unfavorable orientation of discontinuities. The main cause of failure is identified to be the undercutting-induced toppling, which is not amenable to traditional kinematic or rock mass strength-based analyses. Therefore, to recommend a suitable slope angle, numerical models, using UDEC software, were employed to study how various slope angles affect the process of undercutting-induced toppling failures. The UDEC models showed a slope angle of 45° (1H:1 V) to be the most stable angle. However, a 63° (0.5H:1 V) slope angle can significantly reduce the potential for such failures and is therefore more appropriate than the widely used angle of 76° (0.25H:1 V). [ABSTRACT FROM AUTHOR]

Sweden has more than 190 large hydropower dams, of which about 50 are pure embankment dams and over 100 are concrete/embankment dams. This paper presents results from conceptual analyses of the response of typical Swedish rock mass to the construction of a hydropower embankment dam and its first stages of operation. The aim is to identify locations and magnitudes of displacements that are occurring in the rock foundation and grout curtain after construction of the dam, the first filling of its water reservoir, and after one seasonal variation of the water table. Coupled hydro-mechanical analysis was conducted using the two-dimensional distinct element program UDEC. Series of the simulations have been performed and the results show that the first filling of the reservoir and variation of water table induce largest magnitudes of displacement, with the greatest values obtained from the two models with high differential horizontal stresses and smallest spacing of sub-vertical fractures. These results may help identifying the condition of the dam foundation and contribute to the development of proper maintenance measures, which guarantee the safety and functionality of the dam. Additionally, newly developed dams may use these results for the estimation of the possible response of the rock foundation to the construction. [ABSTRACT FROM AUTHOR]

Stability analysis of Surabhi landslide in the Dehradun and Tehri districts of Uttaranchal located in Mussoorie, India, has been simulated numerically using the distinct element method focusing on the weak zones (fracture). This is an active landslide on the main road toward the town centre, which was triggered after rainfall in July-August 1998. Understanding the behaviour of this landslide will be helpful for planning and implementing mitigation measures. The first stage of the study includes the total area of the landslide. The area identified as the zone of detachment is considered the most vulnerable part of the landslide. Ingress of water and increased pore pressures result in reduced mobilized effective frictional resistance, causing the top layer of the zone of detachment to start moving. The corresponding total volume of rock mass that is potentially unstable is estimated to 11.58 million m. The second stage of this study includes a 2D model focussing only on the zone of detachment. The result of the analyses including both static and dynamic loading indicates that most of the total displacement observed in the slide model is due to the zone of detachment. The discontinuum modelling in the present study gives reasonable agreement with actual observations and has improved understanding of the stability of the slide slope. [ABSTRACT FROM AUTHOR]

In undersea gold mines, the development of a water-flow fracture zone and its connection with the aquifer may cause massive water and sand inrush disasters. In this study, approaches including theoretical analysis, numerical simulation and field detection are employed to identify the development height of the water-flow fracture zone caused by undersea mining in the Xinli Zone of the Sanshandao Gold Mine to ensure mining safety. An improved Winkler elastic foundation beam model, considering the coupled influences of seawater pressure and backfill support, was established to calculate the height of the water-flow fracture zone. The result demonstrates that the height of the water-flow fracture zone depends on the elastic modulus of the overburden strata and the compression modulus of the filling material. Then, an experimental study utilizing a custom-made apparatus is conducted to obtain the Winkler foundation compression characteristics of the filling material used in the gold mining operation. The theoretical analyses are confirmed by numerical simulations and show that the height of the water-flow fracture zone decreases with the increase in mining level because the loads from overburden weight decreases with the mining depth. The theoretical analysis, numerical simulation and field detection present that the height of the mining-induced water-flow fracture zone is 39 m, 37 m, and 40.5-45 m, respectively, after mining at the − 135 m level. These values are reasonably consistent, suggesting that the proposed theoretical and numerical models and the utilized field detection method can provide valuable information for determining the overburden stability of an undersea mineral seam and improving mining safety. [ABSTRACT FROM AUTHOR]