| 1. |
- Ahmed, Lamis, et al.
(författare)
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Vibration vulnerability of shotcrete on tunnel walls during construction blasting
- 2014
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Ingår i: Tunnelling and Underground Space Technology. - : Elsevier BV. - 0886-7798 .- 1878-4364. ; 42, s. 105-111
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Tidskriftsartikel (refereegranskat)abstract
- The effect on shotcrete from blasting operations during tunnelling is studied, with focus on young and hardening shotcrete. A finite element model specially adapted for analysis of the shotcrete behaviour is tested, it is able to describe stress wave propagation in two dimensions which is important for cases where shear stresses are dominant. The modelling results are compared with in situ measurements and observations, from construction blasting during tunnelling through hard rock. The comparison shows that the model gives realistic results and can be used to investigate the vulnerability of shotcrete, aiming at compiling recommendations and guidelines for practical use. The given recommendations emphasize that blasting should be avoided during the first 12 h after shotcreting and that distance and shotcrete thickness are important factors for how much additional time of waiting is possibly needed.
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| 2. |
- Ansell, Anders
(författare)
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Investigation of shrinkage cracking in shotcrete on tunnel drains
- 2010
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Ingår i: Tunnelling and Underground Space Technology. - : Elsevier BV. - 0886-7798 .- 1878-4364. ; 25:5, s. 607-613
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Tidskriftsartikel (refereegranskat)abstract
- The presented investigation combines in situ observations, measurements, testing and theoretical modelling. The in situ work was done to map and evaluate the shrinkage related cracking of shotcrete on short and long sections of soft, plastic drains. The occurrence of variation in shotcrete thickness and crack widths were of particular interest. The theoretical analysis focuses on the stresses that can occur due to uneven drying shrinkage in the two-layered shotcrete. The models used include variation in shotcrete thickness and in time of waiting between turns of spraying, with or without watering of the shotcrete. Watering will delay the shrinkage but has no effect on the strength development. Long times of waiting without watering before spraying a second layer will increase the tensile stresses in the shotcrete. It is recommended that the further work is directed towards establishing guidelines for the design of future drain constructions with shotcrete. Different methods for repair and strengthening of cracked shotcreted drains must be developed, tested and evaluated.
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| 3. |
- 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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| 4. |
- Bryne, Lars Elof, et al.
(författare)
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Investigation of restrained shrinkage cracking in partially fixed shotcrete linings
- 2014
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Ingår i: Tunnelling and Underground Space Technology. - : Elsevier BV. - 0886-7798 .- 1878-4364. ; 42, s. 136-143
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates shrinkage of accelerated shotcrete (sprayed concrete), especially in the case of shotcrete sprayed on drains, a part of a tunnel lining not continuously bonded to the rock. One of the goals is to find methods of avoiding shotcrete shrinkage cracks in such drain structures. If cracks yet develop the crack distribution is of great importance, i.e. several fine cracks instead of one wide. By using both steel and glass fibres this may be achieved. A newly developed test set-up for shrinking, end-restrained shotcrete slabs is also presented and evaluated. The performed tests show that the addition of very fine glass fibres could be a solution to the cracking problem. The newly developed test equipment using concrete interacting with an instrumented granite slab represents a realistic way of testing restrained shrinkage. The on-going research focuses on the optimization of the glass fibre addition and the understanding of the interaction between shrinkage and creep of shotcrete.
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| 5. |
- Bryne, Lars-Elof, et al.
(författare)
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Laboratory testing of early age bond strength of shotcrete on hard rock
- 2014
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Ingår i: Tunnelling and Underground Space Technology. - : Elsevier BV. - 0886-7798 .- 1878-4364. ; 41:1, s. 113-119
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates early age bond strength of shotcrete (sprayed concrete), in the case of shotcrete sprayed on hard rock. Shotcrete differs from ordinary, cast concrete through the application technique and the addition of set accelerators which give immediate stiffening. The bond between shotcrete and rock is one of the most important properties. During the very first time after spraying the physical properties and the bond to the rock depend on the set accelerator and the micro structure that is formed. In this work a laboratory test method for measuring early bond strength for very young or early age shotcrete is presented. The newly developed method was tested and evaluated and proved that it can be used for bond strength testing already from a couple of hours after shotcreting.
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| 6. |
- 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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| 7. |
- Draganović, Almir, 1964-, et al.
(författare)
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Filtration and penetrability of cement-based grout : study performed with a short slot
- 2011
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Ingår i: Tunnelling and Underground Space Technology. - : Elsevier. - 0886-7798 .- 1878-4364. ; 26:4, s. 548-559
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Tidskriftsartikel (refereegranskat)abstract
- Filtration of cement-based grout during penetration through fractures in rock is an important issue while sealing the rock around tunnels. Whether a type of grout could be designed to penetrate a fracture of a certain aperture without filtration is an interesting question that needs to be further investigated. This study examines the question of whether grout penetration can be measured using our designed measuring method as well as which factors and processes influence the penetrability and filtration of the grout.The penetration and filtration of grout are complex processes influenced by many factors such as the grain-size curve of the cement, hydration and flocculation, pressure, grain concentration, and the geometry of constriction.The measured results were in agreement with the predicted results, indicating that the filtration process in the given geometry describes correctly.
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| 8. |
- Draganović, Almir, 1964-, et al.
(författare)
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Filtration of cement-based grouts measured using a long slot
- 2014
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Ingår i: Tunnelling and Underground Space Technology. - : Elsevier BV. - 0886-7798 .- 1878-4364. ; 43, s. 101-112
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Tidskriftsartikel (refereegranskat)abstract
- Penetrability of cement-based grout is an important issue when sealing the rock around tunnels and measurement of this property of the grout is needed for designing the grouting process and the development of grout. This paper investigates plug-building or the filtration process in a long slot where a slot constriction is placed relatively far from both the "borehole" and the end of the slot. In this slot, a certain shear stress develops before and after a constriction, which may influence plug-building at the constriction. This method is also compared with short slot and penetrability meter. The smallest groutable fracture for all three measured grouts is reasonably close to 75 mu m. Measurements using the long slot showed better penetrability results compared to the short slot and the penetrability meter. The short slot is more practical and gives reasonably good results. The penetrability meter underestimates the penetrability of the grouts.
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| 9. |
- Gothäll, Rikard, et al.
(författare)
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Fracture-Fracture Interaction during Grouting
- 2010
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Ingår i: Tunnelling and Underground Space Technology. - : Elsevier BV. - 0886-7798 .- 1878-4364. ; 25, s. 199-204
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Tidskriftsartikel (refereegranskat)abstract
- Sealing of self-supporting underground constructions is often done with grouting or pre-grouting, most often with cementitious grouts. In order to achieve sufficient sealing, fine fractures must be penetrated long distances before the grout hardens. This is achieved with high injection pressures that rivals the in situ stress normal to the fractures. In this paper, the interaction of parallel fractures during high pressure grouting is modelled and the influence of the resulting dilation is discussed. Both linear and non-linear fracture stiffness is used in the modelling.
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| 10. |
- Hernqvist, Lisa, 1968, et al.
(författare)
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A hard rock tunnel case study: Characterization of the water-bearing fracture system for tunnel grouting
- 2012
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Ingår i: Tunnelling and Underground Space Technology. - : Elsevier BV. - 0886-7798. ; 30, s. 132-144
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Tidskriftsartikel (refereegranskat)abstract
- Grouting is a common method for reducing water inflow in tunneling projects in hard rock. A good grouting design should be adapted to the water-bearing fracture system in the rock mass. The aim of this work is to present a case study using relevant parameters, to suggest a combination of tests to provide them, and to show how a conceptual model of the water-bearing fracture system can be chosen based on them. The case study, to which the proposed methodology has been applied, is a section of the TASS tunnel at 450 m depth in crystalline rock in Aspo Hard Rock Laboratory in Sweden. In this tunnel project an extensive number of tests provided a fine opportunity for analysis and discussions. A set of functional parameters to describe the rock mass for grouting purposes has been suggested. These are: the hydraulic head h; the hydraulic apertures b of the fractures; fracture frequency P-10; the number and orientation of the major fracture sets; and the flow dimension D-q. A set of investigation methods is suggested, aimed at providing the necessary information for high-precision tunnel projects with strict inflow requirements such as the tunnel project studied. Based on these parameters, it is suggested that a conceptual model of the water-bearing fracture system in the rock mass should be chosen. It is shown how this was done in the case study, first in the investigation stage and then an update in the construction stage. Possible ways to adapt the grouting design to the conceptual model are suggested. Selective grouting may be considered for a rock mass with a 2D fracture system, one dominating water-bearing fracture set, when the tunnel orientation is close to perpendicular to this set. For rock mass with a 3D fracture system, two or more water-bearing fracture sets, systematic grouting may be preferable to avoid "moving the water leakage" from one tunnel section to a neighboring section. When the tunnel intersects a fracture zone the focus should be on sealing this zone.
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