CONTRACTOR: GAMMON CONSTRUCTION LTD
The Mass Transit Railway Corporation (MTRC) was undertaking an extension of the West Island Line (WIL) from Sheung Wan to Kennedy Town. A majority of the tunnelling works were excavated using the drill and blast tunnelling methodology due to the geological conditions. To enable safe and dry storage of explosives, an underground storage magazine had to be constructed within the close vicinity of the three working sites. It was decided to locate the magazines in a 300 m horseshoe type tunnel with 10 separate storage rooms on Victoria Road on the west coastal side of Hong Kong Island.
The Job / The Challenge
Explosive storage rooms had to be 100% watertight and would be permanently lined using sprayed concrete. In order to ensure bonding of the sprayed concrete while still allowing systematic dissipation of ground water to a drainage system, sheet membrane could not be considered for various reasons associated with providing a watertight permanent sprayed concrete lining, bonding issues and creating a controlled drainage path.
The Solution
Normet Hong Kong Limited (formerly TAM International Limited) introduced the TamSeal 800 EVA copolymer spray-applied membrane system, which included the use of TamCrete TopShot (smoothing gunite) and a double-sided geotextile drainage fleece that could be installed at 1.5 m intervals to allow any groundwater to drain from the crown to the invert drainage system at certain locations.
Site trials were undertaken to demonstrate the effectiveness of the Normet solution. Test panels were sprayed in sequence, commencing with the primary lining, followed by a smoothing layer of TamCrete TopShot. A single 3 mm layer of TamSeal 800 grey colour was then applied using a Normet Piccola (dry shotcrete rotor machine) and completed with a final 250 mm thick permanent sprayed concrete layer. Cores were taken through the panel to show the subsequent layers and bonding performance. See the photos below illustrating the core and consistency of the TamSeal 800 prior to PSCL application.
The client (MTRC) was satisfied that the TamSeal 800 system provided the suitability, ease and speed required to ensure the project was completed on time.
The magazine rooms were excavated, and primary sprayed concrete support was installed. The geotextile drainage was then installed using 1 m wide strips at 1.5 m centres, which included the headwall, and a single 500 mm wide strip running along the crown.
The TamSeal 800 system offered several advantages over alternative options considered and proved to be the correct choice.
The speed of preparation, simplicity and flexibility of the application enabled the site construction team to deliver the lined, watertight sections of the project on time and within budget with limited supervision from Normet.