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ABSTRACT: A major international experiment, demonstrating full-scale tunnel sealing technologies and methodologies is being conducted on the 420 Level of Canada's Underground Research Laboratory (URL) with experiment partners from Canada, Japan, France and the USA. The Tunnel Sealing Experiment consists of two instrumented bulkheads, one of low heat high performance concrete, the other of highly compacted bentonitc-sand blocks which seal a central section of the tunnel filled with permeable sand. The central portion will be pressurized incrementally via piping water through boreholes to 4 MPa, to characterize the performance of the bulkheads in preventing axial flow along the tunnel. The bulkheads were designed with cut-off keys to stop flow through the excavation damage zone. The design of these keys required a thorough understanding of the in situ stress tensor. The role of rock mechanics in the design of the Tunnel Sealing Experiment is reviewed along with the construction of this experiment. INTRODUCTION The Underground Research Laboratory (URL) is a geotechnical research and development facility constructed by Atomic Energy of Canada Ltd. (AECL) as part of the Canadian Nuclear Fuel Waste Management Program. The URL, located in south- eastern Manitoba, is constructed in the Lac du Bonnet granite batholith and provides a representative geological environment in which to conduct in situ multidisciplinary experiments, to assess the feasibility and safety of deep geological disposal of nuclear fuel waste. Many countries, including Canada, Japan, France and the United States, are developing concepts for the deep geological disposal of radioactive waste materials. The safety of the respective disposal systems relies on the combined performance of the natural barriers (host rock) and engineered barriers (the waste form, the waste container, the buffer barrier, the room, tunnel and shaft backfill material). Engineered barrier concepts include using bulkheads or plugs to seal shafts and emplacement rooms or both. Bulkheads would be designed as a barrier to water flow and thus potential transport of radionuc!ides. Although the bulkhead would act as a barrier to flow through the backfilled tunnel or shaft, it would also have to be designed to prevent flow through the near-field Excavation Damaged Zone (EDZ) in the rock. Thus it is important to minimize the connected EDZ at the bulkhead location. The Tunnel Sealing Experiment (TSX) has been designed to characterize the sealing potential of well-constructed bulkheads from the perspectives of both engineering performance and safety assessment. Elements of the experiment design include not only the construction of the bulkheads but also the excavation of the tunnel and bulkhead keys. One bulkhead is composed of hand-placed, highly compacted bentonite-sand blocks, while the second has been constructed using Low-Heat High- Performance Concrete (LHI-IPC). A permeable sand fill was placed between the bulkheads and is being pressurized via piping water through boreholes to 4MPa, a value representative of the natural porewater pressure at the 420 Level. Pressure in the tunnel is being increased in a stepwise fashion over a five month period, and the experiment will be operated at full pressure for about one year. At the time of writing, construction is complete and pressurization has begun.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Igneous Rock > Granite (0.69)
- Water & Waste Management > Solid Waste Management (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Power Industry > Utilities > Nuclear (0.89)
An in-situ thermo-hydraulic experiment at the URL
Senjuntichai, Teerapong (University of Minnesota) | Detournay, Emmanuel (University of Minnesota) | Berchenko, Ilya (University of Minnesota) | Chandler, Neil (Atomic Energy of Canada Limited, Whiteshell Laboratories) | Martino, Jason (Atomic Energy of Canada Limited, Whiteshell Laboratories) | Kozak, Ed (Atomic Energy of Canada Limited, Whiteshell Laboratories)
ABSTRACT: This paper is concerned with an in situ thermo-hydraulic experiment carried out at the Underground Research Laboratory of Atomic Energy of Canada Limited. The thermo-hydraulic experiment was designed to determine a hydro-thermal coupling parameter as well as the permeability and the thermal and hydraulic diffusivities of the Lac du Bonnet granite. Several water injection and heater tests were conducted during this experiment. In an injection test, a given volume of water is pumped quasi instantaneously in a sealed-off interval of the borehole, while in a heater test, heat is produced at a constant rate over a certain period (ranging from about one day to several weeks). The experimental set-up involves a heater installed in a sub-horizontal borehole drilled from an underground gallery, and piezometers and thermistors located at different distances from the heater, in auxiliary boreholes drilled from an adjacent gallery. Determination of the material parameters relies on matching the measured pore pressure and temperature responses with the theoretical predictions based on singular solutions of thermoporoelasticity. INTRODUCTION Various geological structures, including thick clay layers, salt domes and hard rock, are being con- sidered in various countries to host nuclear waste repositories. The research described in this paper is associated with the Canadian used fuel program, which is focusing on developing technical capa- bility for the siting, design and safety assessment of a repository in a saturated granitic rock mass. One facility developed in the Canadian Nuclear Fuel Waste Management Program is Atomic En- ergy of Canada Limited's (AECL's) Underground Research Laboratory (URL), in southeastern Man- itoba, Canada. The geological setting of the URL is unique compared to other underground labora- tories in the world because the rock mass of the Lac du Bonnet batholith is essentially ,manufactured below 250 to 300 m depth ?. The Thermal-Hydranlic Experiment (abbrevi- ated to TI?) conducted at the URL included a series of water injection and heater tests. The main objective of TI? is to determine the in situ value of a hydro-thermal coupling parameter (7), characterizing the magnitude of the pore pressure induced by thermal loading, as well as the perme- ability (n) and the thermal (c.) and hydraulic (c) diffusivities of the Lac du Bonnet granite. In this paper, the experimental set-up of THE as well as some results from a back-analysis of the experiments are presented. These results are ob- tained by matching the time and the amplitude of the peak of the pore pressure and tempera- ture responses with theoretical predictions based on the singular thermoporoelastic solutions of a fluid source and a heat source. The analysis pre- sented in this paper is a follow-up of the prelimi- nary results discussed by Berchenko et al. (1998).
- North America > Canada (0.75)
- North America > United States (0.46)
- Geology > Geological Subdiscipline > Geomechanics (0.79)
- Geology > Rock Type > Igneous Rock > Granite (0.45)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.79)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.54)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Production logging (0.49)
ABSTRACT: Microseismic (MS) and Acoustic Emission (AE) monitoring is being carried out as part of the Tunnel Sealing Experiment (TSX) at the 420m level of Atomic Energy of Canada's Underground Research Laboratory (URL). A 40m long tunnel was excavated in the direction of the maximum in situ stress, with approximate dimensions of 4.4m horizontally and 3.5m vertically. These two dimensions were chosen to reduce the magnitude of the high stress concentrations, which occur in the roof and floor of sub-horizontal tunnels at the URL. Two bulkheads have been constructed and keyed into the tunnel to create a chamber in granite, which can be pressurised to ambient pore pressure (4 MPa). This paper presents the results of the AE/MS monitoring of the excavation phase of the TSX and the velocity interferometry measurements taken to monitor the time-dependent development of the excavation disturbance zone (EDZ). The results support stress modelling predictions and show that induced microcracking is limited to within a 0-2m shell around the excavations. THE TUNNEL SEALING EXPERIMENT The TSX is designed to examine the performance of concrete and bentonite based tunnel bulkheads subjected to high hydraulic gradients in granite. Figure I shows a schematic of the TSX, while Figure 2 shows the main tunnel (room 425) as well as the other tunnels associated with the experiment which provide access for instrumentation and drainage boreholes. The chamber between the bulkheads will be pressurised to approximately 4 MPa which is representative of the ambient pore pressures at 420m depth in the rock. Instrumentation will monitor the seepage around and through each bulkhead. Additionally stresses and displacements in each bulkhead will be recorded. A second phase of the experiment will involve determining temperature effects by heating the water in the chamber to about 85°C. Room 425 was excavated using a drill and blast technique between January and March 1997. The 40m long tunnel was excavated in the direction of the maximum principal stress, o?, and the cross- section geometry was elliptical, with approximate dimensions of 4.4m horizontally and 3.5m vertically. This tunnel shape was chosen to reduce the magnitude of the high compressive stress concentrations that occur in the roof and floor of subhorizontal tunnels at the URL. The circular Mine-by tunnel (room 415), which was excavated in the direction of 02, promoted the maximum stress- induced damage zone. This resulted in significant MS and AE activity (Young and Collins, 1997), the formation of a process zone (Read and Martin, 1996) and subsequent break-out notches in the roof and floor of the tunnel. The excavation of various elliptical shaped tunnels on the 420 Level (Read and Chandler, 1996) has shown that breakout notches can be stopped from forming.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Igneous Rock > Granite (0.91)
ABSTRACT: In the past ten years, several large-scale underground experiments have been conducted at AECL's Underground Research Laboratory (URL) to address geomechanics issues related to the disposal of nuclear fuel waste in Canada. Two key rock mechanics issues that have been studied are the development of near-field excavation damage and the stability of underground excavations in granite under various boundary conditions. This paper presents an overview of four of these in situ experiments and highlights the main findings in terms of rock mechanics considerations for nuclear waste disposal. INTRODUCTION In Canada, research into the disposal of nuclear fuel waste has focused on the concept of deep geological burial in an underground disposal vault. In designing excavations associated with such a vault, a key objective is to maintain stable rock mass conditions around each opening throughout the vault's life cycle, while at the same time minimizing excavation damage. During this time period, the rock mass will be subjected to mechanical loads generated by underground excavation, support loads introduced by buffer and backfill materials, and thermal loads generated by the emplaced nuclear fuel waste. Other loads, such as those associated with glaciation, are also possible over the long term. As a first step to designing stable openings, the rock mass response to excavation and to subsequent loading, and factors that may affect this response, must be understood. To address these and other related issues, Atomic Energy of Canada Limited (AECL) constructed the Underground Research Laboratory (URL) approximately 120 km NE of Winnipeg, Manitoba, Canada within the Lac du Bonnet granite batholith near the western edge of the Canadian Shield. As shown in Figure 1, within the first few hundred metres of the surface at this site, the granite contains subvertical joint sets and several major low-dipping thrust faults (called Fracture Zones), and has undergone secondary alteration. Below Fracture Zone 2 and its splays, the granite is interrupted by granodiorite dykes, but is sparsely fractured and relatively unaltered.
- Geology > Rock Type > Igneous Rock > Granite (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Water & Waste Management > Solid Waste Management (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
- Energy > Oil & Gas > Upstream (1.00)
INTRODUCTION ABSTRACT: Water-quality monitoring and hydraulic testing in fractured bedrock aquifers involves two important tasks: 1) identifying the hydraulically active fractures intersecting the borehole; and 2) inferring how the specific entry or exit ports in the borehole wall are connected to large-scale flow paths in the region surrounding the borehole. Effective characterization of fractured bedrock flow results when hydraulically active fractures and fracture zones are first identified using flow logs, and then the hydraulic properties of these active zones are given by subsequent hydraulic tests. A more difficult technical problem is relating the hydraulic properties of the few specific fractures that serve as borehole entry ports to the large-scale hydraulic properties of the surrounding rock mass. This problem is addressed through a generalized borehole flow model inversion formulated so that the boundary conditions at the outer edge of the boundary layer can be inferred from the properties of measured borehole flow. Boreholes provide the usual means of sampling the subsurface distribution of hydraulic properties in aquifer studies. However, .typically a few boreholes are not adequate to provide an effective characterization of the distribution of permeability in heterogeneous fracture flow systems. Numerous studies (Paillet & Allen 1996; Paillet et al. 1987) demonstrate that fracture density and local fracture aperture almost never correlate with local measurements of fracture zone permeability as given by standard hydraulic tests. Even when accurate measurements of fracture or fracture zone permeability can be made for the rocks immediately adjacento the borehole, a prohibitively large number of data points would be needed to characterize the large-scale permeability of the aquifer (Tiedeman et at. 1998). ?II?us, there is a critical need for techniques that can define such large-scale characteristics of fractured-rock aquifers as the vertical thickness, horizontal extent, and average hydraulic conductivity of fracture zones on the basis of measurements made in a limited number of boreholes. Monitoring and hydraulic testing in fractured bedrock aquifers involve two important tasks: 1) identifying the hydraulically active fractures intersecting the borehole; and 2) inferring how the specific entry or exit ports in the borehole wall are connected to large-scale flow paths in the region surrounding the borehole. High-resolution flow logging provides measurements that relate to both of these objectives. Flow profiles under ambient and steady pumping can be used to identify the few fractures that contribute most inflow to the borehole (Paillet et al. 1996; Paillet and Pedler 1996). Flow log data can also be used to infer the far-field boundary conditions associated with the borehole flow distribution, and the changes in that flow distribution over time. These boundary conditions are shown to depend on the large-scale geometry and volume-averaged hydraulic conductivity (hereafter denoted by the general term hydraulic properties) of the aquifer. Therefore, borehole flow experiments provide information needed to "see" beyond the "screen" of individual fracture entry ports in specifying the hydraulic characteristics of the far-field aquifer.
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Faults and fracture characterization (1.00)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Production logging (1.00)
ABSTRACT: This paper presents the results of stress measurements (HTPF method) made in 4 deep exploratory boreholes for the future base tunnel of the high speed railway project Lyon-Turin (Franco-Italian Alps). With respect to the expected values due to gravity forces alone, the results in the heart of the Arebin Massif globally show a marked deficit of vertical stress, and an excess of horizontal stress. The analysis of these results has been performed by using numerical 2D and 3D modeling, to study the respective influence of local topography and of global tectonic stresses INTRODUCTION The 52 km running tunnel of the proposed Lyon- Turin railway link will be excavated through different geological formations with various tectonic contacts. The overburden over most of the route is greater than 1000 m and it reaches 2000 - 2500 m in the Arebin Massif, which is structurally a regular gueiss-micaschistic dome on the Franco-Italian border (Fig. 1). The knowledge of the in situ stress field is fundamental to tunnel design, especially in cases (as this one) where excavations are to be made at great depth in complex tectonic massifs. The excavation deformation behavior and the occurrence of such phenomena as rockburst, bulking and squeezing highly depend on the in situ stress field. Efforts to reduce uncertainty in cost and time of the project has led Alp tunnel GEIE, in charge of tunnel design, to make stress measurements with the HTPF method (Hydraulic Testing on Preexisting Fractures, Comet 1986, Wileveau 1997), in 15 boreholes. The results of these tests show a scatter of information on values and directions of stress vectors. The interpretation of such results needs complex analysis of the topographical and geological-geotechnical context. For example, the stress measurements in the Arc river valley, where 8 HTPF measurements are available, generally show (Burlet et al. 1995) the major principal stresses horizontal and perpendicular to the valley axis.
ABSTRACT: This paper describes the development of a borehole stability model capable of considering certain chemo-mechanical processes that are operative iv. drilling fluid-shale interactions. Specifically, phenomena related to osmotic and poroelastic processes are included. A generalized plane strain solution is utilized which fully couples the chemical potential and deformation of shale. Drilling fluid parameters such as mud weight and salt concentration can be optimized to alleviate borehole instability when using oil-based or water-based muds. The user can choose the Drucker-Prager failure criterion or the Mohr-Coulomb criterion when conducting stability analyses. The model was used to investigate the impact of drilling fluid chemistry on the stability of an inclined wellbore in shale. The results demonstrate that osmosis significantly impacts fluid flux into the formation whereby stability can be achieved by increasing the salinity of the drilling mud. However, the contribution of osmosis to hole stability is overestimated by the ion exclusion model. Preliminary results of a boundary element model with ion transfer indicate that the diffusion of ions progressively decreases and eventually eliminates osmosis by reducing the chemical potential gradient between the mud and the formation. INTRODUCTION When holes are drilled for petroleum production, more than 90% of the drilled length involveshales. Prior to drilling, a shale formation is in a state of hydraulic, thermal, chemical, and stress equilibrium. Drilling action disturbs this equilibrium and introduces gradients of stress, pore pressure, temperature and chemical potentied in the rock material surrounding the hole. To reestablish equilibrium, shale deforms, swells and may det?. riorate causing borehole instability. In the past, the petroleum industry has used oil-based muds to prevent wellbore instability. However, due to their toxicity, oil-based muds are environmentally hazardous and can lead to very large remedial costs. Water-based muds provide an attractive alternative, but have shown poor shale-drilling performance (van Oort et al. 1996). The extent to which a shale is disturbed due to excavating a well can be assessed by a suitable analysis of the forces imposed on the rock by the disequilibria resulting from the drilling action. The chemomechanical processes causing shale deterioration and borehole instability while drilling have been studied by a number of investigators. Although significant progress has been made (Mody and Hale, 1993; Onaisi et ed. 1993; van Oort et al. 1996; Sharma et al. 1998), an adequate tool for analyzing shale deformatioh while drilling is not presently available. The development of such a tool requires consideration of those. parameters which drive transport processes in a borehole stability model. In this paper the macroscopic processes of osmosis, and ion transfer are described and their potential contribution to shale instability are delineated. This is followed by the presentation of a borehole stability model which considers the effects of hydraulic and chemical potentieds. Results of the application of the model are discussed and future improvements are outlined.
- North America > United States > Oklahoma (0.29)
- North America > United States > North Dakota (0.28)
- Europe > Norway > Norwegian Sea (0.24)
- Well Drilling > Wellbore Design > Wellbore integrity (1.00)
- Well Drilling > Drilling Fluids and Materials (1.00)
ABSTRACT: In existing poroelastic borehole models, the pore fluid conditions at the borehole wall are simply assumed as: a constant pore pressure for penetrating models, or no flux across the wall for impermeable models. In reality, the pore fluid boundary conditions at the walls may be much more complicated. This paper presents the newly-developed poroelastic solution for inclined boreholes with time-dependent pore pressure or the pore fluid flow at the wall. The effects of the pore fluid boundary conditions on the borehole stability are also analyzed. INTRODUCTION It has already been recognized that the pore fluid boundary conditions, such as the pore pressure or the flow rate at the borehole walls, affect the borehole stability significantly. However, there is a lack of analysis of such effects. Indeed, this effect can hardly be analyzed and quantified, if the conventional theories such as elastic borehole models are applied. Rather than taking into account the real fluid flow conditions at the borehole walls, two limiting cases of finally permeable (penetrating) and totally impermeable walls are usually assumed in practice. In conventional elastic models, since the pore pressure around the borehole cannot be determined appropriately, it is simply assumed to be the same as either the well pressure for the permeable case or the virgin formation pressure for the impermeable case (Fj?er et al. 1992). Recently-developed poroelastic inclined borehole models (Cui et al. 1997,1998), which accurately account for coupling between the deformable rock matrix and the pore fluid flow, indicated that the pore pressure around the borehole could be very different from the well pressure or the formation pore pressure, especially, within a certain time period after excavation and fluid injection. Although the poroelastic borehole models accurately predict the pore pressure field around the borehole, they were also developed only for the two limiting cases. In these models, the pore pressure at the borehole wall is assumed to be the same as the well pressure for the permeable case; and, the flow rate across the wall is not allowed for the impermeable case. However, the pore pressure at the borehole wall may be time-dependent, instead os a constant; it can be quite different from the well pressure, because of the existence of a filter cake; or, the flow rate at the borehole wall is a given function of time, instead of a known pore pressure at the wall. In this work, the poroelastic solutions for an inclined borehole with arbitrary time-dependent conditions of pore pressure and flow rate at the borehole walls are presented. Using these solutions, the effects of the time-dependent pore pressure at the borehole walls and pore fluid withdrawals on the borehole stability are investigated.
ABSTRACT: Engineering projects, such as deep tunnel and nuclear waste repository, may involve very deep overburden. As the depth at the project site increases, the underground temperature tends to elevate. This study aims to develop a reasonable methodology for estimating underground rock temperature under deep overburden. This paper proposes a methodology of modular analysis for estimating deep underground rock temperature. The proposed methodology involves the finite-element method and nonlinear optimization method. The proposed analysis assumes that the distribution of underground temperature is solely due to twodimension thermal conduction. After verification, numerical experiments demonstrate that the distribution of underground temperature significantly depends on the thermal conductivity of undergroUnd rock. Parametric study illustrates that the anisotropy of thermal conductivity and the topography of ground surface also affect the distributions of temperature and thermal gradient. This study also discusses the sources of error for estimating the underground temperature. INTRODUCTION Engineering projects, such as deep tunnel and nuclear waste repository, may involve very deep overburden. Due to temperature gradient, the ground temperature tends to raise 0.031-0.033øC per meter of depth in average. As a result, the rock temperature around a deep tunnel must increases with the depth of overburden. As the overburden and temperature increase, the complexity and difficulty of the engineering construction will become more and more challenging. Take the Apenine tunnel across Alps for example, the overburden is about 2 km, rock pressure is up to 50-60 MPa, and the maximum rock temperature is 64øC. In addition to deep tunnel, projects concerning radioactive waste depositary and geothermal resource also require the knowledge of ground temperature condition [Darnes and Motre, 1978; Inada and ? 1989]. Several deep tunnels are undergone planning in Taiwan, the influence of underground temperature on the design and construction of these deep tunnels are seriously concerned. In view of the importance of correctly estimating the ground temperature, this paper presents an inverse approach for estimating the distribution of ground temperature from the measured temperature profile along drilled wells. The inverse approach combines a finite-element method and a nonlinear optimization procedure. As long as the ground temperature distribution and the thermal expansion coefficient of rock can be determined, the thermal stresses adjacent to an excavated tunnel can also be evaluated. In order to determine the correct ground temperature distribution, the thermal flux on the external boundary of the problem domain is assessed by nonlinear optimization procedure such that the calculated temperature profile matches the measured values along the drilled wells. With the boundary thermal flux determined, the correct distribution of ground temperature then can be resolved.
- Water & Waste Management > Solid Waste Management (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
ABSTRACT: A new borehole breakdown model with external in-situ stresses as well as internal grouting pressure is proposed in this study. For this, a bifurcation analysis together with a tensile fracturing model have been employed to simulate the crack propagation and eventual breakdown of the borehole. Numerical examples are also introduced to verify the proposed model on crack propagation and comparison with experimental data on shear and tensile cracking mode are made wherever possible. INTRODUCTION A grouting technique which has been widely used to increase the bearing capacity of in-situ soil/rock can be classified into several methods according to the characteristics and properties of the grout. Among others, a permeation or penetration grouting can be used where rock joints are scattered along the civil structures such as tunnels and dams and, in this case, grouting material is penetrated into the rock joints so that the material properties of in-situ rock will be enhanced. In this regards, a new design approach on the permeation grouting has been proposed by authors [1]. Meanwhile, a fracturing grouting can be considered where in-situ soil/rock properties are weathered and cracks due to high injection pressure are expected. In this case, artificially generated cracks are filled with grouting material which is composed of cement and additional admixture. However, fracturing process and design approach on the fracturing grouting have not yet been properly established. In this study, the fracturing mechanism of the borehole (grouting hole) due to high injection pressure is investigated to estimate the fracturing pressure and, using this, reinforcement design of the grout can be performed. Theory of the hydraulic fracturing or borehole breakout can be directly used to the analysis and design of the fracturing grouting. As is well known, the hydraulic fracturing was introduced to estimate the in-situ stresses and several theories on the hydraulic fracturing have been suggested and new field of applications have also been proposed [2-4]. In this study, two modes of cracking process, i.e. a shear and a tensile crack, are investigated using a bifurcation theory and a tensile strength model, respectively. Also considered here is the combined cracking mode in which an initial shear crack is subsequently changed into the tensile crack mode by external stresses. However, a compresslye crack model which has been reported in [5] is not considered here. Currently, the fracturing mode is limited to the newly generated cracks and no interaction with the preexisting joints or cracks is accounted for. Future work will have to include the interaction mechanism between joints or cracks and, from this, the grouting effect will be considered accordingly.