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2013FallShotcreteEMag

Goin’ Underground collection channel and brought down to an support or, in coal mines, to prevent methane evaporative drainage channel; and ingress. Yilmaz10 contains a good review of • The suitability of the membrane is dependent various TSL products and their properties. 5 mm on the geology and technology available, for (0.2 in.) of “medium” strength TSL is equivalent example, presently not suitable for water to 50 mm (2 in.) of SCL, in terms of structural bearing stratigraphy such as sands. performance at 1 day old. Achieving a substantially Thin skin liner (TSL) or so-called “Superskin” impermeable layer on the extrados of the tunnel, products, such as Masterseal 865 or Tamseal, outside impermeable permanent sprayed concrete, could fulfill the dual role of an initial sealing coat would obviate the need for a secondary lining. to provide safe access to the face before the The primary lining would carry all water and primary lining is sprayed and the first line of ground loads in both the short- and long-term. If defense against water ingress. This technology necessary, a finishing layer could be applied later has been around since the 1990s and has been for aesthetics or fire protection. This represents trialed in the mining industry as a structural the ultimate solution in terms of efficiency and sustainability. Trials are ongoing to investigate Table 1: Typical sequence for a 6m diameter SSL tunnel (1 excavation round) the best technologies to achieve this. Thin skin liner Tunnel construction Duration/ Total time/ age (tunnel Single Shell Lining—A Practical stage/description minutes minutes shell)/minutes Application Excavate and muck 1 one metre tunnel For a single shell lining, as described pre- excavation round viously, to be a viable option (and thereby provide Spray thin skin liner a significant saving to the lining cost), there would 2 sealing layer for 10 – 15 10 – 15 have to be a feasible construction method that tunnel circumference would provide a watertight or near-watertight tunnel, i.e. a continuous waterproofing layer for Spray thin skin liner sequential tunnel excavation and construction. If 3 sealing layer over 5 – 10 15 – 25 10 – 15 testing can demonstrate that sprayed concrete tunnel face could be sprayed on to a partially cured, thin- 4 5 – 10 20 – 35 15 – 25 skinned liner with a sufficient bond then theClean up and move out sprayer kit following sequence could be proposed: Set up SCL spraying Stages 1 and 2 show the proposed typical 5 5 – 10 25 – 45 20 – 35 sequence of the single shell lining with therobot Spray structural SCL waterproof membrane sprayed against the 6 Approx 30 excavated surface and acting as the sealing layer.layer The major difference with this methodology is that a 200 mm (8 in.) overlap is left to ensure that there is continuity in waterproofing between the 1 m (3.3 ft) rounds. Stage 3 indicates an application of a finishing layer. For a typical 6 m (19.7 ft) diameter tunnel, Stage 1, based on typical construction rates, could be broken down to the timeline shown in Table 1. Therefore, the minimum curing time for the membrane/sealing layer unless construction is paused would be something in the order of 30 minutes. Following discussion with BASF, it was proposed to carry out some initial testing of “The minimum curing time for the mem- brane/sealing layer unless construction is paused would be something in the order of 30 minutes” Fig. 9: Practical application of SSL 50 Shotcrete • Fall 2013


2013FallShotcreteEMag
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