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Results
Long-Term Stability For a Proposed Nuclear Waste Deep Geological Repository: Bruce Nuclear Site, Ontario, Canada
Damjanac, Branko (Itasca Consulting Group, Inc) | Martin, Derek (University of Alberta) | Diederichs, Mark (Queens University) | McCreath, Dougal (Laurentian University) | Lam, Tom (Nuclear Waste Management Organization)
Abstract: Ontario Power Generation (OPG) is proposing a Deep Geologic Repository (DGR) for the long-term management of low and intermediate level radioactive waste generated at OPG owned or operated nuclear facilities. As envisioned, the DGR would be excavated within an 840 m thick, Paleozoic age, sedimentary sequence underlying the Bruce nuclear site in the Municipality of Kincardine, Ontario, Canada. Lateral development of the DGR would occur in the Cobourg Formation, an argilla-ceous limestone that is overlain by 200 m of Ordovician shale. As part of investi-gations conducted to assess the safety of the DGR, geomechanical analyses were carried out to evaluate rock-mass barrier integrity over a timeframe of 1Ma. The primary concern regarding long-term performance of the emplacement rooms is their degradation over time when subjected to different loading conditions, include-ing time-dependent strength degradation, seismicity, gas generation within the repo-sitory and multiple glacial loading/unloading cycles. This paper describes a series of analyses performed to explore rock mass stability and barrier integrity surrounding the waste emplacement rooms. Results indicate that while damage in the near field may arise over time, the capacity of the enclosing formation barrier to contain and isolate the waste is not affected. 1 INTRODUCTION Nuclear Waste Management Organization (NWMO), on behalf of Ontario Power Generation (OPG), is managing the development of a Deep Geologic Repository (DGR) for Low and Intermediate Level Waste (L&ILW) at the Bruce nuclear site, located in the municipality of Kincardine in Ontario, Canada. The site-specific, long-term geomechanical stability study was conducted as a part of the DGR site character-rization activities. The analy-ses included assessments of DGR cavern, pillar and shaft stability, and the evolution of damage and deformation of the surrounding rock mass in response to excavation activities and the long-term dynamic geological conditions expected at the site.
- North America > Canada > Ontario (1.00)
- North America > United States > Texas > Kleberg County (0.24)
- North America > United States > Texas > Chambers County (0.24)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.36)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.31)
- Water & Waste Management > Solid Waste Management (1.00)
- Government > Military (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
- Energy > Oil & Gas > Upstream (1.00)
Abstract: An underground powerhouse cavern was designed for a hydroelectric power project in Turkey using nonlinear finite element method and parametric analyses. The main goals of the design were the limiting of the cavern displacements and plastic zones. Laboratory tests and in-situ stress measurements were conducted to obtain the material parameters and the stress condition in the rock. The large variance in the model parameters obtained from the field and laboratory tests, as well as the multitude of possible modeling approaches prompted a two phase parametric study using non-linear finite element analyses. First, the effect of key material parameters on the design goals was evaluated using an approach called tornado diagram and an elastic-perfectly plastic constitutive model. Later, the analysis choices regarding the use of the different constitutive models and failure criteria were assessed using the elastic-perfectly-plastic (EPP) and elastic-brittle constitutive models with the Hoek-Brown (HB) and Mohr-Coulomb failure criteria. The conclusions of the study reflect much greater sensitivity of the design goals on the UCS and GSI values compared to the other material or modeling parameters. Moreover, possible shortcomings of an EPP analyses were revealed; such analyses may falsely assure a designer yielding low convergence displacements and meager support requirements. 1 INTRODUCTION Koprubasi Hydroelectric Power Plant (KHPP) is an 81 MW energy generating system which is built in north-western Turkey. The project consists of a 108 m high embank-ment dam and an underground cavern housing for the electric turbines. The cavern, with the dimensions of 58m(L)x22m(W)x38m(H), is going to be built 160m under the ground in medium quality, highly jointed granodiorite. The main purpose of this study was to obtain a cost-benefit balanced design of the Koprubasi powerhouse cavern and support system, limiting the convergence displacements & the plastic zones around the cavern.
- Asia > Middle East > Turkey (0.54)
- North America > United States (0.46)
- Energy > Power Industry (0.88)
- Energy > Oil & Gas > Upstream (0.48)
Abstract: The ONKALO rock characterisation facility is located in the Olkiluoto area in the west coast of Finland. It aids in collecting the further data needed for the appli-cation of the construction license for the repository of spent nuclear fuel that will be submitted in 2012. It provides an opportunity to develop excavation techniques and final disposal techniques in realistic in situ conditions. The goal of the facility is to provide information for the design of the planned nuclear repository. The ONKALO design method can be considered as a prediction and observation method. Typical rock conditions can be handled using the Observational Method (Peck 1969) ap-proach, and more complex cases (e.g. stress-induced damage, extensively cracked areas, crossings, heat-affected zones, etc.) are handled with numerical and analytical predictions. The design method can be divided into five phases: description of infor-mation on existing geology, site investigation and interpretation, obtaining rock mass parameters, calculations, and design. The method has undergone continuous im-provement during the different excavation stages and as new rock mechanical chal-lenges have been detected. Examples of Eurocode compatible rock reinforcement de-sign are shown. Finally, the suitability of the current design method for the design of the spent nuclear fuel repository is discussed. 1 INTRODUCTION Rock engineering design is a challenging and multi-disciplinary task, which ranges from optimisation of the layout, excavation direction and tunnel shape and design of water proofing and grouting to design of rock reinforcement. In typical urban rock engineering, the main problems lie in water proofing and cost-minimisation while maintaining a sufficient level of quality. In ONKALO, the main issue is to meet the high safety and technical requirements while maintaining an acceptable excavation speed and cost. Additional problems arise from imposed material restrictions and from exceptional environmental conditions of ONKALO.
Abstract: The possibilities to analyze rock engineering problems have dramatically changed over the last thirty to fifty years. While in the "old" times "design" was based on personal or "second hand" experience, we now have the means and methods to establish models, which are close to reality, and analyze nearly any kind of problem. Reviewing the current international practice, one can see that only in very few cases the approach is adequate to the problem and tools available are used appropriately. Still there is a lot of empiricism in the basic design (RMR, Q, etc). Taking more "shortcuts", generally the strongly discontinuous rock mass usually is "homogenized" with the help of questionable empirical routines. After this "characterization" in many cases numerical simulations are performed, which do not resemble the real situation at all. Based on those analyses the previously empirically determined supports are then checked on their utilization. It is surprising that such approaches are still accepted. It can only be attributed to the fact that the ground itself has a high potential for self stabilization, and mistakes made during design not always become obvious. Instead of the mentioned questionable practices, problem oriented approaches should be used. 1 INTRODUCTION The limited knowledge of the ground structure and quality, as well as the lack of appropriate design tools in the past has forced to heavily rely on experience when designing rock engineering structures, such as foundations, slopes, or underground structures. Non foreseen events during execution of the work not only represent a hazard to people involved and third parties, but also generally lead to costly remediation measures with associated time overruns. Empirical design methods have been accepted for a long time, owing to the lack of appropriate design methods and non developed theory.
Abstract: An extremely complex sequence of excavations for the new City Line rail project are currently being undertaken beneath and in connection to the existing "T-Centralen" subway in central Stockholm, Sweden. Rock cover between the roof of the City Line tunnels and the floor of the existing blue line station is in the range of 2–5 m. The excavation of cross passages, concourse tunnels and escalator shafts result in the existing blue line rock pillars being undermined. An extensive site investigation indicated that the ground conditions would consist of fair to good quality gneiss and granite. The gneiss dominated areas were forecast to contain low shear strength dis-continuities with smooth fracture surfaces coated with chlorite. Design of the excava-tion sequence and rock reinforcement was based on the results of a 3D numerical model. Each critical area was then specifically analysed for pillar and arch stability by assessing critical discontinuity orientations/parameters and a number of scenarios were defined for each area. These were subsequently included as design criteria in the construction documents. Furthermore a number of tollgates were included in the de-sign. The purpose of the tollgates was to provide check points, which the contractor could not pass until the design criteria (rock mass quality, discontinuity orienta-tions/properties, reinforcement work, deformation measurements etc.) for the tollgate were met. The design was reviewed in connection with each tollgate and if necessary modified prior to passage of the tollgate. The purpose of the model was to provide a clear picture of the orientation and location of discontinuities in relation to the planned and existing excavations. This required careful mapping of the excavations and surveying of the discontinuity traces using a total station together with laser scanning. Results from the mapping were subsequently incorporated into a 3D discontinuity model.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Metamorphic Rock > Gneiss (0.45)
Underground Water Problem In Ankara - Istanbul High Speed Railway Construction Tunnel No: 36
Ogul, K. (TCDD) | Gicir, A. (TCDD) | Topal, I. (Dumlupinar University) | Aksoy, C. O. (Dokuz Eylul University) | Posluk, E. A. (Istanbul University) | Aldas, G. U. (Ankara University) | Ozer, S. C. (Istanbul Technical University)
Abstract: Ankara – Istanbul high speed railway construction project consists of 32 tunnels. Tunnel 36 is one of these tunnels and water problem encountered during the excavation of this tunnel is studied in this paper. Total length of that tunnel, which is excavated with NATM, is 4096 meters and located between km 239+934,00 and km: 244+030,80. Tunnel is excavated in Porsuk Miocene Formation (sandstone, clay stone, gravel alternation) and Akpinar Formation (limestone-sandy limestone) which have same ages. Excavations started in the tunnel entrance portal in Porsuk Formation and water inflow has happened while passing Akpinar Formation with dip slip fault at km.241+003,80. Water inflow had negative impact on the units of initial support system and it caused deformations in the lipper-bench especially at the locations where construction hadn't been finished. Deformations at these locations are occurred in this form; softening of the formations, which carry the footplates, with the effect of water inflow thus, formations couldn't carry the loads on them and settlements occur. In this study, the problems caused by underground water in the tunnels and solution methods are discussed. 1 INTRODUCTION Groundwater infiltration into tunnels can pose a serious risk during the execution of works and reduce the speed of excavation. The presence of water in a rock massif can induce some difficulties and increase the cost of excavation (Jansson, 1979; Cesano et al., 2000; Day, 2004). Furthermore, the drawdown produced by excavations can cause hydrological, hydrogeological and environmental impacts on groundwater dependent ecosystems (Vincenzi et al., 2009). Among the common hydrogeological impacts in densely populated areas are the drying of private wells or springs close to the tunnel axis due to the water table drawdown (Sjolander-Lindqvist, 2005) and base flow reduction in rivers that drain the basins crossed by the tunnel (Vincenzi et al., 2009).
- Asia > Middle East > Turkey > Istanbul Province > Istanbul (0.63)
- Asia > Middle East > Turkey > Ankara Province > Ankara (0.63)
- Geology > Structural Geology > Tectonics (0.94)
- Geology > Geological Subdiscipline > Environmental Geology > Hydrogeology (0.89)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.46)
Abstract: The objective of this paper is to estimate water seepage from the upper reservoir of Azad pumped storage power plant (PSPP), based on combined geotech-nical investigations and geostatistical methods. In order to select the optimum water tightening alternative, such as clay blanket, concrete cover (or concrete lining), geomembrane, asphalt cover and etc, estimation of water seepage from the reservoir is essential. Six exploratory boreholes were drilled at the pumped storage reservoir area and permeability tests (Lugeon tests) were conducted in all of them. Records at the boreholes have been considered as the main source for seepage calculations. Due to expansion of upper reservoir and a few boreholes, distribution of permeability and permeability changes in the reservoir area is not indicator for reservoir. In this research using geostatistical method (Kriging), Lugeon values have been estimated for walls of reservoir. According to correspondence between estimated permeability distribution and geological conditions, the estimated values are acceptable. In addition results show that in about 60% of tests, permeability is very high and potential of wa-ter seepage is very dangerous. Afterward, seepage was estimated for reservoir by us-ing both analytical (Vedernikov method) and numerical method. Results from both methods are very close together and the average of seepage is around 280000 m3/day according to analytical and numerical results. Results show that because of using appropriate permeability distribution, the estimated values of water seepage are acceptable and reliable. Due to the high amount of water seepage and economical value of water in this region, water tightening is necessary. 1 INTRODUCTION Azad Pumped Storage Power Plant (PSPP) Project has aimed to store hydraulic poten-tiality using pumping system under low load conditions of the power supply network and generating electricity by turbine and generator under peak load conditions of the network.
- Europe (0.28)
- Asia > Middle East > Iran (0.16)
Abstract: The rock mass, by nature, includes fractures at different scales, which in-fluence the hydro-mechanical behavior of formation. In many engineering applications the formation is porous, for example, tunneling in sandstone layers or production from a sandstone reservoir. The fluid flow in a fractured porous formation would be partly through the formation but the major flow path is the fracture. This, however, depends on different parameters including the formation permeability and more importantly the applied stresses. In this paper, 2D fluid flow simulations are performed using FLU-ENT on a simple lab scale porous formation which includes one fracture plane. One phase flow with water in a laminar regime was assumed for the analysis. The simula-tions were conducted for fractures with different surface roughness and also for-mations with different permeabilities. Also, the fracture aperture was changed to in-vestigate the corresponding effect of applied normal stresses to the fracture plane on permeability. The results indicate how the contribution of fracture in fluid flow reduc-es at smaller apertures and also larger fracture surface roughness. In general, similar results were observed for larger formation permeabilities. 1 INTRODUCTION It is well established that formation permeability is a function of the in-situ stresses (Zhang et al., 1999; Bai et al., 1999; Somerton et al. 1975). Through several laboratory and field tests, empirical correlations have been proposed to estimate formation per-meability in relation to the in-situ stresses (Zhang et al., 1999). The importance of fracture properties and fluid flow changes with respect to different overburden pres-sures and stress-state conditions have also been reported (Vance, 2005). In this study X-ray CT scan was used to estimate fracture height distribution for fluid flow studies within the fracture plane and also investigate the fluid transfer mechanism between fracture and matrix.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.74)
Abstract: Determining the permeability of fractured rock masses is very important in different field of engineering works. Fractured rock mass permeability is calculated by analytical methods and numerical methods. In numerical methods two different approaches are considered, DFN (Discrete Fracture Network) methods and DPM methods. In contrast to DFN methods Dual Porosity Medium (DPM) is a medium that permeability of the rock matrix cannot be neglected. However, evaluating of rock mass permeability for these cases in previous works was limited to regular joint sets or simple fracture geometry such as en echelon fracture pattern, and they did not consider the effect of fracture density, or the effect of matrix permeability and fracture aperture pattern on Representative Elementary Volume (REV), and therefore the permeability in such studies was not reliable. This was the motivation of this study. Rock matrix was generated with some kind of tessellation elements called Voronoi elements (VE). Then stochastic DFN models were generated with different fracture densities and aperture patterns to fit on the matrix model. The results show that increase in matrix permeability leads to higher rock mass permeability. 1 INTRODUCTION Dual Porosity is a concept that defines the relatively high permeability for the rock mass matrix, which means that the medium with Dual Porosity has the capability of directing the fluid flow through the matrix. In this case, the matrix has an important role in transporting the fluid in the rock mass, on other hand, the permeability of rock mass consists of two variables: fracture system permeability and matrix permeability. The studies often neglect the permeability of the matrix, with this claim that the matrix permeability is low and it has a very limited effect on overall permeability. This study has been performed on a numerical structure to investigate this fact.
Abstract: For many engineering rock works, such as rock slopes, foundations of dam, underground excavations; calculating the permeability and evaluating Representative Elementary Volume is very important. The Effective Medium Theory (EMT) ap-proach is an alternative method for network permeability calculation. In this way a fracture network can be replaced by a regular network of conductors that are connect-ed to each other at nodes. Then by evaluation suitable effective conductance, permea-bility is calculated. Using Monte Carlo technique, stochastic DFN models were generated with a large number of realizations with the same fracture density and different aperture patterns when distributed fracture trace lengths are correlated/uncorrelated with fracture aper-ture distributions and directional permeability components are calculated with devel-oped new code and compared with numerical results. The results show that the calculated mean values of permeability and approximated permeability tensor with EMT method is well fitted with the numerical simulation results in all fracture patterns. INTRODUCTION Calculating of permeability components is very important for understanding the hy-draulic behavior of fractured rock masses. Permeability of fractured rocks is calculated using different methods such as analytical methods reported in (Snow 1969, Oda 1985) or numerical methods reported in (Long et al 1982, Priest 1993, Min et al 2004, Baghbanan 2008). Compared with analytical methods which are mostly used for sim-ple lattice networks, numerical methods are applied for the extensive condition and more complicated models such as large Discrete Fracture Network (DFN) models. However they need large computing resources and are very time consuming. Using Effective Medium Theory (EMT) for calculation the permeability of a lattice network is also reported in the literature as alternative method for numerical solution (Kirkpat-rick 1973, Bernasconi 1974, Harris 1990, Zimmerman &Bodvarsson 1996, Jankovic 2003, Fedrov et al 2005, Baghbanan & Dayani 2009, Dayani & Baghbanan 2010).