| 1. |
- Butron, Christian, 1978, et al.
(author)
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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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In: Tunnelling and Underground Space Technology. - : Elsevier BV. - 0886-7798. ; 25:2, s. 114-121
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Journal article (peer-reviewed)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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| 2. |
- Fransson, Åsa, 1971, et al.
(author)
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A swedish grouting design concept: Hydraulic testing and selection of grout
- 2012
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In: Geotechnical Special Publication. - Reston, VA : American Society of Civil Engineers. - 0895-0563. - 9780784412350 ; :228 GSP, s. 1691-1700
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Conference paper (peer-reviewed)abstract
- Some grouting boreholes take no grout and some boreholes take too much, two extremes related to grouting technique, grout properties and the properties of fractures intersecting the boreholes. Successful sealing of rock and soil demands an adequate description of the system to be grouted as a basis for grouting design and selection of grouting material. The basis for this Swedish concept of grouting design is the individual fractures and the hydraulic apertures, b, of these fractures. The hydraulic aperture is an important parameter to describe the grouting behavior and is used to determine if the grout can enter the fractures, the penetrability. The hydraulic aperture also determines the penetration length in addition to grout parameters e.g. yield stress, τ0, and viscosity, μg as well as grouting pressure and time. Knowing these parameters, a proper grouting technique can be adapted. Important input for both design and performance are simple and practical tests of rock and grout and the intention of this paper is to present a testing procedure and give examples from laboratory and field experiences that the approach actually works. © 2012 American Society of Civil Engineers.
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| 3. |
- Fransson, Åsa, 1971, et al.
(author)
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Characterization of fractured crystalline rock: two Swedish in situ field experiments
- 2014
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In: 1st International Discrete Fracture Network Engineering Conference, 20-22 oct 2014, Vancouver, Canada.
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Conference paper (peer-reviewed)abstract
- Construction of a nuclear waste repository requires information and an understanding of the fractured rock. The Swedish concept for nuclear waste deposition that is currently being developed by the Swedish Nuclear Fuel and Waste Management Co (SKB) includes a natural barrier in the form of crystalline rock, and engineered barriers in the form of bentonite and a copper canister. This paper aims to present two in situ field experiments: the first is the Large fractures experiment and the second is BRIE, the Bentonite Rock Interaction Experiment. Important issues include possible deformation (shearing) of fractures and deformation zones influencing the localization of canisters, and fluid flow, resulting in hydration of the bentonite. The aim of Large fractures is to further develop strategies and integrated investigation and modelling methodology for the identification and characterization of geological structures to ensure that (size) determination of large fractures or minor deformation zones to a greater extent can be based on real properties and to a lesser degree on a criterion related to the existence of a full perimeter fracture – tunnel intersection. BRIE is a field experiment which addresses the hydraulic interaction between the system components of compacted bentonite and the near-field host rock composed of hard and fractured bedrock. The above experiments are presented in terms of investigations performed to obtain discrete fracture descriptions. Grouting of fractures intersecting the investigation borehole of the Large fractures experiment was designed based on field data and a decrease in flow from above 200 liters/min to below 1 liter/min was achieved. The magnitude of the transmissivity of the fracture/deformation zone that was grouted indicates a large fracture size. This is also indicated by the ongoing integrated interpretation (geology, hydrogeology and geophysics). Results from BRIE show that hydration is uneven and is controlled by the main conductive fracture, highlighting the need for a relevant fracture description.
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| 4. |
- Fransson, Åsa, 1971, et al.
(author)
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Effektiv spricköppning och bruksval baserat på vattenförlustmätningar
- 2011
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In: Bergmekanikdagen 2011/ 12:e ISRM kongressen. ; , s. 13 s.-
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Conference paper (other academic/artistic)abstract
- Inträngningsförmågan hos cementbruk i spalter har undersökts grundligt. Emellertid styrs bruksspridning av två processer; inträngning av bruket genom sprickorna och blockering och filtrering av bruket i förträngningar längs flödesvägen. I denna uppsats utvärderas den för dessa processer och ett givet bruk kritiska spricköppningen i en spricka (ett spricksystem) med varierande sprickvidd. Med utgångspunkt från detta ges sedan en enkel metod för att skatta sprickvidd och välja brukstyp och reologiska egenskaper för injektering av ett borrhål i en injekteringsskärm.Inledningsvis analyseras möjliga flödesvägar genom ett system av kanaler med perkolations- teori. Denna visar att sprickviddsfördelningen och förgreningarna av möjliga kanaler bestämmer den effektiva öppningen. Resultaten av denna analys kan redovisas med en enkel numerisk modell där inflytandet av medianvidden och variabiliteten kan varieras. Resultaten verifieras sedan med fältdata från Äspölaboratoriet och Nygårdstunneln, som nyligen byggts norr om Göteborg. Sammantaget visar detta att den hydrauliska sprickvidden också är ett rimligt mått på den effektiva spricköppningen (tröskelvärdet för genomflöde) för injekteringsmedlet.Baserat på dessa resultat har ett diagram konstruerats för att välja mellan cementbruk och fintätningsmedel (t.ex. silica sol). Diagrammet baseras på en bestämning av den hydrauliska sprickvidden på grundval av vattenförlustmätningar eller inflödesmätningar i injekteringsborrhålen under antagandet att en spricka står för det huvudsakliga flödet. Även detta diagram har verifierats med data från Äspölaboratoriet och Nygårdstunneln. Analyserna pekar på att en hydraulisk sprickvidd av 50-100 mym är gränsen för vad som kan tätas med cementinjektering. Detta överensstämmer också med resultaten från undersökning av inträngningsförmågan hos cementbruk. Diagrammet är enkelt att använda i fält och en användning bör kunna minska risken för fel bruksval i s.k. nollhål för cement vid injekteringsprojekt.
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| 5. |
- Fransson, Åsa, 1971, et al.
(author)
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Estimation of deformation and stiffness of fractures close to tunnels using data from single-hole hydraulic testing and grouting
- 2010
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In: International Journal of Rock Mechanics and Minings Sciences. - : Elsevier BV. - 1365-1609. ; 47:6, s. 887-893
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Journal article (peer-reviewed)abstract
- Sealing of tunnel sin fractured rocks is commonly performed by pre- or post-excavation grouting. The grouting boreholes are frequently drilled close to the tunnel wall, an area where rock stresses can be low and fractures can more easily open up during grout pressurization. In this paper we suggest that data from hydraulic testing and grouting can be used to identify grout-induced fracture opening, to estimate fracture stiffness of such fractures, and to evaluate its impact on the grout performance. A conceptual model and a method are presented for estimating fracture stiffness. The method is demonstrated using grouting data from four pre-excavation grouting boreholes at a shallow tunnel (50 m) in Nygard, Sweden, and two post-excavation grouting boreholes at a deep tunnel (450 m) in Aspo HRL, Sweden. The estimated stiffness of intersecting fractures for the boreholes at the shallow Nygard tunnel are low (2-5 GPa/m) and in agreement with literature data from field experiments at other fractured rock sites. Higher stifness was obtained for the deeper tunnel boreholes at Aspo which is reasonable considering that generally higher rock stresses are expected at greater depths. Our method of identifying and evaluating the properties and impact of deforming fractures might be most applicable when grouting takes place in boreholes adjacent to the tunnel wall, where local stresses might be low and where deforming (opening) fractures may take most of the grout. (C) 2010 Elsevier Ltd. All rights reserved.
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| 6. |
- Fransson, Åsa, 1971, et al.
(author)
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Geology, water inflow prognosis and grout selection for tunnel sealing: Case studies from two tunnels in hard rock, Sweden
- 2010
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In: ITA-AITES World Tunnel Congress. Vancouver, Canada, Maj 17-19.
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Conference paper (peer-reviewed)abstract
- Successful sealing of tunnels by injection of grout into the fractured rock demands knowledge concerning the geological and hydrogeological conditions. This paper aims at presenting how a description of the geology and hydrogeology can be used as a basis for a grouting design. Important issues that are considered here are: identification of the extent of the grouting based on inflow requirements and a prognosis of tunnel inflow; and selection of grout based on the performance of grouting materials. Two tunnel sections from two different tunnels in crystalline rock were used as case studies. The first tunnel section (70 m) is found in Äspö Hard Rock Laboratory (south east Sweden) at 450 m depth. The rock is sparsely fractured and the main rock type is a diorite. The second tunnel section (36 m) is found in the Hallandsås tunnel (south west Sweden) excavated through a horst and at approximately 100 m depth. The fracture network is well connected. In this section the rock consists of gneiss and amphibolite.A conclusion based on the two case studies is that the principal descriptions of the geology and hydrogeology for the two tunnel sections identify general differences between the two tunnels. This explains in part the deviation found between early inflow prognoses and the measured inflows. Further, the estimated hydraulic aperture from hydraulic tests can be used as a basis for selection of grout. Finally, the fracture frequency or the variation in fracture frequency (e.g. between neighboring borehole- or tunnel sections) in combination with hydraulic tests indicate what areas to focus on when grouting.
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| 7. |
- Fransson, Åsa, 1971, et al.
(author)
-
Hydromechanical characterization of fractures close to a tunnel opening: A case study
- 2012
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In: ISRM International Symposium - EUROCK 2012.
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Conference paper (peer-reviewed)abstract
- Important factors influencing the hydromechanical behavior of a fracture are in situ rock stresses (natural and induced) as well as hydraulic heads, fracture orientation, connectivity and fracture geometry, including their infillings. Particular attention is given to larger, water-conducting fractures that intersect or are close to a tunnel. For the Bentonite Rock Interaction Experiment (BRIE) at the Äspö Hard Rock Laboratory (HRL) in Sweden, the interaction between rock and bentonite in a deposition borehole is of particular interest. The BRIE experiment is being conducted at a depth of 420 meters in crystalline rock. This paper presents results from the initial identification, characterization and modeling of a small number of fractures close to the tunnel opening. So far, these fractures have been identified as the most important water-conducting fractures. In this identification and characterization exercise, core-drilled, vertical, three-meter deep investigation boreholes were made in the tunnel floor. Logging of natural hydraulic heads in boreholes and hydraulic tests, along with borehole and tunnel mapping in combination with modeling, indicate small deformations. This was also confirmed by deformation measurements performed in the boreholes. The description of the site will be further updated and revised and additional investigations into the link between stress history, fracture geometry and selection of fracture mechanical properties will be of particular interest.
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| 8. |
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| 9. |
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| 10. |
- Gustafson, Gunnar, 1945, et al.
(author)
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Steering Parameters for Rock Grouting
- 2013
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In: Journal of Applied Mathematics. - : Hindawi Limited. - 1110-757X .- 1687-0042. ; 2013, s. Art. no. 269594-
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Journal article (peer-reviewed)abstract
- In Swedish tunnel grouting practice normally a fan of boreholes is drilled ahead of the tunnel front where cement grout is injected in order to create a low permeability zone around the tunnel. Demands on tunnel tightness have increased substantially in Sweden and this has led to a drastic increase of grouting costs. Based on the flow equations for a Bingham fluid the penetration of grout as a function of grouting time is calculated. This shows that the time-scale of grouting in a borehole is only determined by grouting over-pressure and the rheological properties of the grout, thus parameters that the grouter can choose. Pressure, grout properties and the fracture aperture determine the maximum penetration of the grout. The smallest fracture aperture that requires to be sealed thus also governs the effective borehole distance. Based on the identified parameters that define the grouting time-scale and grout penetration an effective design of grouting operations can be set up.
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