Since cut and cover tunnels such as subways are generally constructed under groundwater level or below, waterproofing is necessary to provide sufficient water-tightness (Fig. 1). However, conventional waterproofing cannot provide such enough protection, resulting in the possibility of water damage to the facilities inside tunnels.
More effective waterproofing has therefore been expected strongly. The Railway Technical Research Institute (RTRI) has developed an adhesive advance waterproofing sheet that chemically clings to the framing concrete thanks to a special resin and is superior in water-tightness and workability.
This sheet consists of four layers (Fig. 2) and uses a special EVA (ethylene/vinyl acetate copolymer) resin combined with adhesive polymers for the concrete contact surface to enhance water-tightness. Since the new sheet is lighter than conventional ones, it can be handled easily, has good workability and adheres easily to other sheets.
The indoor performance test demonstrated that the new sheet ensures sufficient water-tightness and adhesion even under high water pressure corresponding to a water head difference of 50 m and has sufficient compliance characteristics without rupture against concrete cracks with a width of around 6-mm (Fig. 3). The on-site workability test also demonstrated that the whole sheet adheres tightly to the framing concrete without damage during concrete cast (Fig. 4,) confirming its good applicability to engineering practice.