| 1. |
- Axelsson, Magnus, 1974, et al.
(författare)
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A robust method to determine the shear strength of cement-based injection grouts in the field
- 2006
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Ingår i: Tunnelling and Underground Space Technology. ; 21:5, s. 499-503
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Tidskriftsartikel (refereegranskat)abstract
- There is no standardised method to directly determine the shear strength of grouts in the field. Determining the shear strength would make it possible to calculate the penetration length of cement-based grouts and hence establish a design of the grouting procedure. By developing a new robust method that consists of a stick sinking in the grout, a direct measurement of the shear strength can be made, using the same set up as the separation test. The sink of the stick depends on the shear force interaction between the grout and the stick, and hence the shear strength of the grout can be determined. To verify the results, the shear strengths obtained with the stick are compared with measurements of the shear strength made with a rotational rheometer in the laboratory. The comparison shows good agreement; hence the stick can be used in the field to determine the yield strength of cement-based grouts.
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| 2. |
- Axelsson, Magnus, 1974, et al.
(författare)
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Design criteria for permeation grouting in hard rock at great depths
- 2008
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Ingår i: Proceedings World Tunnel Congress 2008, Underground facilities for better environmnet and saftey. ; 1, s. 510-520
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Tidskriftsartikel (refereegranskat)abstract
- Grouting at tunnelling in hard rock at great depths below the groundwater table, when constructing a nuclear waste repository for example, makes special demands on the strength of the grout in order to resist groundwater forces. The aim of this study is to distinguish the most important parameters to ensure that suitable grouting can be performed at large depths. Initially, laboratory studies were conducted in order to determine the most critical parameters. The results from the laboratory tests were used in a field study at the Äspö Hard Rock Laboratory in Sweden. The results indicate that the most important characteristics for the rock are the fracture aperture and the groundwater gradient and for the grout: a resolute grouting pressure and sufficient early strength. This implies that for cementitious grouts the yield stress is important and for non-cementitious grouts it is the shear strength prior to gelling. The results emphasise the need to perform hydraulic characterisation of the rock mass in advance. The results also show the importance of performing a proper grouting, especially at large depths where a decreased penetration length of the grout increases the risk of a high gradient and hence erosion of the grout.
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| 3. |
- Axelsson, Magnus, 1974, et al.
(författare)
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Grouting with high water/solid-ratios. Literature and laboratory study
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The grouting methodology in Sweden is developing towards a more extensive use of low water/cement-ratios. The main reason for this development is the better stability of the lower w/c-ratio grouts meaning that the water separation is less than for higher w/c-ratios. However, grouting in low permeable rock or in clay-filled fractures often is performed with high w/c-grouts with better sealing efficiency. Another method that involves high w/c-ratio grouting is “grout thickening” where the grouting starts with a high w/c-ratio and successively lower w/c-ratio is used. In this study the penetration and the stop mechanisms of suspension grouts have been investigated. The study started with a literature survey, from which hypothesis are formed and tested in the laboratory. The laboratory method used was sand column tests. The column, height 1 m and diameter 0.1 m, was filled with 0.9 m sand which was characterised by hydraulic measurements. The grouting was performed with Myanit, a suspension consisting of crushed dolomite with similar rheological characteristics as cement. The main advantage of using Mynait is that it is an inert material. This implies that it will keep it characteristics throughout the grouting and it will not harden with time. In order to obtain different relationships between grout grain size and theoretical aperture and hence groutability, different ratios between water and the solids were used as well as different sand grain distribution.Generally, the conclusions are that the penetration increased with higher water/solid-ratios and the penetration stops due to three different mechanisms. In apertures that are too small for the grout to enter, the sealing occurs due to blocking of the entrance. At the limit on what is possible to penetrate, a higher w/s-ratio leads to a further penetration compared to a grout with lower w/s-ratio. The suspension is not moving as a united front, rather it is a more dilute grout in the front, which leads to sealing by single suspensions grains that blocks the pathway. In larger aperture, the grout penetrates more united and the penetration stops due to equilibrium between driving forces and friction forces.The results implies that the use of “grout thickening” in the field will lead to that the initial higher w/c-ratio grout will penetrate a larger area of the fracture plane and suspension grains will successively plug the constrictions. The thicker grout will then penetrate the larger openings and the combined effect will give decreased permeability compared to only use one w/c-ratio.
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| 4. |
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| 5. |
- Axelsson, Magnus, 1974, et al.
(författare)
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Stop mechanism for cementitious grouts at different water-to-cement ratios
- 2009
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Ingår i: Tunnelling and Underground Space Technology. - : Elsevier BV. - 0886-7798. ; 24:4, s. 390-397
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Tidskriftsartikel (refereegranskat)abstract
- Cementitious grouts are the most commonly used grouting material in the world. The general concept of grouting is to propagate the grout in a sufficiently large volume in the grouted medium and hence to have a controlled penetration. This study has been performed in order to determine and test the different mechanisms that result in stoppage of the penetration of cementitious grouts. This is performed as sand column tests in a laboratory study, coupled with grouting in the field. The result shows that three different stop mechanisms can be identified depending on the ratio between the grain size of the grout and the available opening. At an opening up to three times the size of the largest grout grains, penetration does not occur due to clogging of the grains. For an opening larger than five times the largest grain the penetration is unrestricted and stoppage occurs due to equilibrium between the driving and resistance forces. Between these ratios, a transition area exists where the water content determines the penetrability and the stoppage is governed by a filtration process for the grout grains. This implies that grouting with higher water-to-cement ratios results in a larger penetration area and hence by applying the mixture-thickening method during grouting an increased sealing efficiency can be obtained. (c) 2008 Elsevier Ltd. All rights reserved.
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| 6. |
- Axelsson, Magnus, 1974, et al.
(författare)
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The PenetraCone, a new robust field measurement device for determining the penetrability of cementitious grouts
- 2010
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Ingår i: Tunnelling and Underground Space Technology. - : Elsevier BV. - 0886-7798. ; 25:1, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- One of the most crucial parameters for successful grouting is to ensure that the grout can penetrate the necessary apertures. For the most commonly used grout, cementitious grout, the available methods for determining the ability to penetrate apertures involves several measurements with different meshes or similar, which need to be evaluated. However, during the grouting process in the field there is rarely any time for evaluation and the most commonly used field method today stipulates a mesh width through which a certain volume need to pass. This implies that only an indirect measurement of the penetrability is performed. In order to perform direct and fast field measurements of the penetrability, a new, robust measuring device has been developed at Chalmers University of Technology in Gothenburg, Sweden. The device is named PenetraCone and the measuring part consists of a gap that is formed between two conical cylinders. The penetrability characteristics are measured by decreasing this gap as grout flows through. The gap is measured using a dial indicator gauge. Initial tests with the PenetraCone show that two characteristic gaps or widths can be evaluated. The width as the grout flow goes from continuous flow to dripping is termed bfilter and when the flow stops completely it is termed bstop. The parameter bfilter is related to the commencement of clogging or filtration of the cementitious grout. This means that for apertures larger than bfilter the cement passes unrestricted but for narrower apertures filtration will commence. This filtration process will occur in apertures down to bstop, which indicates the smallest aperture that the cement can pass through and for apertures below bstop the cement will not penetrate at all. The device is easy to use and the tests show that consistent values are obtained. The accuracy seems good enough for use as a control of the penetrability of cementitious grouts in the field. For use in production, the PenetraCone should be placed on the grouting rig, after the mixer, so that direct measurements can be performed on the grout that will actually be used for grouting. By relating the measured parameters to the penetrability requirements, quick decisions regarding the quality of the grout can be made directly on the grouting rig.
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| 7. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
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Ageing of cementitious materials for storage of nuclear waste
- 2011
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Ingår i: Nordic Concrete Research. ; Publication No. 43, s. 429-432
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Konferensbidrag (refereegranskat)abstract
- This paper presents an on-going research project dealing with ageing process of cementitious materials in a perspective of hundreds and thousands years. As it is risky to use empirical models for extrapolation of performance data from relatively short term experiments, a mechanism-based (chemo-mechanical coupled) model for safer prediction of longevity of concrete in storage facilities for nuclear waste is needed. The project work involves thermodynamic modeling, development of accelerated aging tests, physical, chemical and mineralogical characterization of young and aged cementitious materials, including mechanical, transport (diffusivity) properties, binding (adsorption) capacities and surface complexation (charging) behavior.
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| 8. |
- Butron, Christian, 1978, et al.
(författare)
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A Swedish grouting design concept: Grouting with silica sol in the Nygård and Törnskog tunnels
- 2012
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Ingår i: Geotechnical Special Publication. - Reston, VA : American Society of Civil Engineers. - 0895-0563. - 9780784412350 ; :228 GSP, s. 826-835
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Konferensbidrag (refereegranskat)abstract
- The scope of this paper is to present two tunnel grouting design case studies where the waterproofing aimed not only to reduce the water inflow to a specified level, but to minimize the number of dripping spots by means of pre-excavation grouting. Every grouted section of around one hundred meters in both tunnels used relevant parameters from the rock and the grout material properties to develop an adequate, pre-excavation grouting design. Both tunnels, constructed in crystalline rock, used silica sol as the main grouting material and were evaluated later by means of control boreholes and dripping characterization. Control boreholes showed a decrease in the transmissivity in these sections, and the dripping characterization showed a reduction in the number of dripping spots compared to the rest of the tunnel, where this pre-excavation grouting concept was not used. This led to minimization of the number of drains used, which was clearly visible in the Nygård case, suggesting that the designs were successful and confirming that an understanding of the rock and grout properties is crucial to the design concept.
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| 9. |
- Butron, Christian, 1978, et al.
(författare)
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Assessment of the transmissivity field in fractured rock: A case study in the tass tunnel
- 2009
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Ingår i: Nordic Symposium of Rock Grouting.
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Konferensbidrag (refereegranskat)abstract
- Water Pressure Tests (WPTs) among other hydraulic tests were conducted in each borehole before and after the pre-excavation grouting of a test tunnel in the Äspö HRL (Hard Rock Laboratory) built in 2008 and 2009 “the TASS tunnel”. This paper shows how data from WPTs can give information on the connectivity and asses the transmissivity fields of fractured rock. The results showed that the connectivity range of the rock before grouting is approximately 3 m, which seems to be a common range in crystalline fractured rocks. Results clearly indicate that the most conductive parts of each fan were where the grout has penetrated the most during grouting. They also show that the reduction of the transmissivity in the rock by means of grouting is about four orders of magnitude within the studied rock volume of a fan. This sealing takes place easily on planar fractures where the transmissivity is high (a few conductive fractures that give the major contribution to the borehole transmissivity) and what is left unsealed is a highly channelized system. This channelized system will be extremely difficult to hit by future boreholes, which will make post-grouting a very complex task.
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| 10. |
- Butron, Christian, 1978, et al.
(författare)
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Drip sealing of tunnels in hard rock: A new concept for the design and evaluation of permeation grouting
- 2010
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Ingår i: Tunnelling and Underground Space Technology. - : Elsevier BV. - 0886-7798. ; 25:2, s. 114-121
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a new pre-excavation grouting concept to prevent dripping and reduce the inflow into a railway tunnel. For this purpose, the tunnel's roof was drip-sealed using colloidal silica and the walls and invert of the tunnel were grouted with cement. The grouting design process followed a structured approach with pre-investigations of core-drilled boreholes providing parameters for the layout. Water pressure tests and pressure volume time recordings were used for the evaluation. Results showed that the design was successful: the total transmissivity was reduced from 4.9 x 10(-08) m(2)/s to the measurement limit (1.6 x 10(-08) m(2)/s), and the dripping was reduced to eight spots from the roof. Improved rock characterisation showed that the grout hole separation was within the transmissivity correlation length and that grouting efficiency depends to a large extent on the dimensionality of the flow system of the rock mass. (c) 2009 Elsevier Ltd. All rights reserved.
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