| 1. |
- Cnattingius, S, et al.
(författare)
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The epidemiology of stillbirth
- 2002
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Ingår i: Seminars in perinatology. - : Elsevier BV. - 0146-0005. ; 26:1, s. 25-30
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Feng, Q., et al.
(författare)
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A new method for in-situ non-contact roughness measurement of large rock fracture surfaces
- 2003
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Ingår i: Rock Mechanics and Rock Engineering. - : Springer Science and Business Media LLC. - 0723-2632 .- 1434-453X. ; 36:1, s. 3-25
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a new method for in-situ non-contact measurements of fracture roughness by using a total station (TS). The TS is a non-reflector geodetic instrument usually used for measuring control points in surveying and mapping. By using a special-developed program, the TS can be used as a point-sensor laser scanner to scan a defined area of the fracture surface automatically, in field or in laboratory, at a distance away from the target surface. A large fracture surface can be automatically scanned with a constant interval of the sampling points, both within a defined area or along a cross-section of the exposed rock face. To quantify fracture roughness at different scales and obtain different densities of the scanned points, the point interval can be selected with the minimum interval of I rum. A local Cartesian co-ordinate system needs to be established first by the TS in front of the target rock face to define the true North or link the measurements to a known spatial co-ordinate system for both quantitative and spatial analysis of fracture roughness. To validate the method, fracture roughness data recorded with a non-reflector TS was compared with the data captured by a high-accuracy 3D-laser scanner. Results of this study revealed that both primary roughness and waviness of fracture surfaces can be quantified by the TS in the same accuracy level as that of the high accuracy laser scanner. Roughness of a natural fracture surface can be sampled without physical contact in a maximum distance of tens of meters from the rock faces.
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| 3. |
- Feng, Q., et al.
(författare)
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Measuring fracture orientation at exposed rock faces by using a non-reflector total station
- 2001
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Ingår i: Engineering Geology. - 0013-7952 .- 1872-6917. ; 59:1-2, s. 133-146
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of fracture orientation are usually taken by using a compass-inclinometer device on exposed rock faces. The drawbacks when using this method is that it is time-consuming if many fractures are measured and that measurement might be impossible if the rock face cannot be safely reached physically. To improve field mapping of rock fractures, a method for applying a non-reflector total station to measuring fracture orientation is presented in this paper. A non-reflector total station is a geodetic device that captures three-dimensional co-ordinates of target points without using a reflector. Therefore, physical touching the rock surfaces is no longer required. To determine a fracture orientation, co-ordinates of a set of points on the exposed fracture surface are captured at a distance from the rock face. The best-fit plane of the exposed fracture surface is defined by the co-ordinates of the target points, and the orientation (e.g. dip angle and dip direction) of the fracture surface is determined as that of its best-fit plane. This paper presents the technical procedure and a portable system designed for the field mapping of fracture orientation. Results of a case study performed at an exposed rock face are also included.
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| 4. |
- Hudson, J. A., et al.
(författare)
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Coupled T-H-M issues relating to radioactive waste repository design and performance
- 2001
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Ingår i: International Journal of Rock Mechanics And Mining Sciences. - 1365-1609 .- 1873-4545. ; 38:1, s. 143-161
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Tidskriftsartikel (refereegranskat)abstract
- In this paper. coupled thermo-hydro-mechanical (THM) issues relating to nuclear waste repository design and performance are reviewed. Concise statements. that were developed from DECOVALEX discussions, on the current state-of-knowledge are presented. Section 1 describes the THM background and the interface with performance assessment (PA). The role of THM issues in the overall repository design context is amplified in Section 2, which includes a review of the processes in terms of repository excavation. operation and post-closure stages. It is important to understand the overall context, the detailed THM issues, the associated modelling and how these issues will be resolved in the wider framework. Also, because uncoupled and coupled numerical codes have been used fur this subject, there is discussion in Section 3 on the nature of the codes and how the content of the codes can be audited. To what extent does a particular code capture the essence of the problem in hand? Consideration is also given to the associated question of code selection and the future of numerical codes. The state-of-knowledge statements are presented in Section 4 under 11 headings which follow the repository design sequence. The overview conclusion is that A predictive THM capability is required to support repository design because precedent practice information is insufficient. Many aspects of THM processes and modelling are now well understood and there is a variety of numerical codes available to provide solutions for different host rock and repository conditions. However, modelling all the THM mechanisms in space and time is extremely complex and simplifications will have to be made - if only because it is not possible to obtain all the necessary detailed supporting information. Therefor, an important step is to clarify the THM modelling requirement within the PA context. This will help to indicate the complexity of THM modelling required and hence the models. mechanisms, type of computing, supporting data, laboratory and in situ testing, etc, required. An associated transparent and open audit trail should be developed. We also include comments from reviewers and highlight four outstanding issues which are currently being studied in the DECOVALEX III programme.
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| 5. |
- Min, Ki Bok, et al.
(författare)
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Determining the equivalent permeability tensor for fractured rock masses using a stochastic REV approach : Method and application to the field data from Sellafield, UK
- 2004
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Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 12:5, s. 497-510
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Tidskriftsartikel (refereegranskat)abstract
- A numerical procedure to determine the equivalent permeability tensor of a fractured rock is presented, using a stochastic REV (Representative Elementary Volume) concept that uses multiple realizations of stochastic DFN (Discrete Fracture Network) models. Ten square DFN models are generated using the Monte Carlo simulations of the fracture system based on the data obtained from a site characterization program at Sellafield, Cumbria, UK. Smaller models with varying sizes of from 0.25 mx0.25 m to 10 mx10 m are extracted from the generated DFN models and are used as two-dimensional geometrical models for calculation of equivalent permeability tensor. The DFN models are also rotated in 30degrees intervals to evaluate the tensor characteristics of calculated directional permeability. Results show that the variance of the calculated permeability values decreases significantly as the side lengths of the DFN models increase, which justifies the existence of a REV. The REV side length found in this analysis is about 5 m and 8 m with 20% and 10% acceptable variations, respectively. The calculated directional permeability values at the REV size have tensor characteristic that is confirmed by a close approximation of an ellipse in a polar plot of the reciprocal of square roots of the directional permeability.
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| 6. |
- Rao, Qiuhua, et al.
(författare)
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Shear fracture (Mode II) of brittle rock
- 2003
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Ingår i: International Journal of Rock Mechanics And Mining Sciences. - 1365-1609 .- 1873-4545. ; 40:3, s. 355-375
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Tidskriftsartikel (refereegranskat)abstract
- Mode II fracture initiation and propagation plays an important role under certain loading conditions in rock fracture mechanics. Under pure tensile, pure shear, tension- and compression-shear loading, the maximum Mode I stress intensity factor, K (sub I max) , is always larger than the maximum Mode II stress intensity factor, K (sub II max) . For brittle materials, Mode I fracture toughness, K (sub IC) , is usually smaller than Mode II fracture toughness, K (sub IIC) . Therefore, K (sub I max) reaches K (sub IC) before K (sub II max) reaches K (sub IIC) , which inevitably leads to Mode I fracture. Due to inexistence of Mode II fracture under pure shear, tension- and compression-shear loading, classical mixed mode fracture criteria can only predict Mode I fracture but not Mode II fracture. A new mixed mode fracture criterion has been established for predicting Mode I or Mode II fracture of brittle materials. It is based on the examination of Mode I and Mode II stress intensity factors on the arbitrary plane theta ,K (sub I) (theta ) and K (sub II) (theta ), varying with theta (-180 degrees < or =theta < or =+180 degrees ), no matter what kind of loading condition is applied. Mode I fracture occurs when (K (sub II max) /K (sub I max) )(K (sub IIC) /K (sub IC) ) and K (sub II max) = K (sub IIC) at theta (sub IIC) . The validity of the new criterion is demonstrated by experimental results of shear-box testing. Shear-box test of cubic specimen is a potential method for determining Mode II fracture toughness K (sub IIC) of rock since it can create a favorable condition for Mode II fracture, i.e. K (sub II max) is always 2-3 times larger than K (sub I max) and reaches K (sub IIC) before K (sub I max) reaches K (sub IC) . The size effect on K (sub IIC) for single- and double-notched specimens has been studied for different specimen thickness B, dimensionless notch length a/W (or 2a/W) and notch inclination angle alpha . The test results show that K (sub IIC) decreases as B increases and becomes a constant when B is equal to or larger than W for both the single- and double-notched specimens. When a/W (or 2a/W) increases, K (sub IIC) decreases and approaches a limit. The alpha has a minor effect on K (sub IIC) when alpha is within 65-75 degrees . Specimen dimensions for obtaining a reliable and reproducible value of K (sub IIC) under shear-box testing are presented. Numerical results demonstrate that under the shear-box loading condition, tensile stress around the notch tip can be effectively restrained by the compressive loading. At peak load, the maximum normal stress is smaller than the tensile strength of rock, while the maximum shear stress is larger than the shear strength in the presence of compressive stress, which results in shear failure.
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