Caldecott Station, Singapore

CONTRACTOR: SAMSUNG C&T CORPORATION

As part of the Thomson Line & Circle Line Interchange Project in Singapore, Contract T213 for the construction of Caldecott Station, an underground Mass Rapid Transit (MRT) station, and associated tunnels was awarded to Samsung C&T Corporation for a contract sum of S$285 million. Scheduled for completion in 2020, the station will become an interchange connecting the future Thomson Line with the Circle Line.

Upon completion of Contract T213, the interchange station situated underneath Toa Payoh Rise will bring further convenience and connectivity to commuters working and residing in the Thomson Road and Toa Payoh Rise area. This interchange will also provide easier access to the Singapore Association of the Visually Handicapped, Lighthouse School, Lions Home for The Elders, Mount Alvernia Hospital and MacRitchie Reservoir.

Caldecott Station consists of a twin tunnel and one three-arch tunnel with a total area of approximately 3,200 square metres. When it is completed in 2020, commuters will be able to enjoy a direct route between Woodlands and Caldecott Stations in 25 minutes as compared to the current 40 minutes it takes to travel along the North South Line and transfer to the Circle Line at Bishan.

The Land Transport Authority (LTA) wanted to try a new waterproofing system as the PVC sheet membrane system used in past projects had not been very effective, with problems of continued water ingress into operating tunnels. This is particularly evident in the area around complicated interfaces with other structures and where complicated joint details form weak zones, with almost 90% of them requiring leak repair. The LTA was seeking to address this issue and started to look for a solution. Normet proposed the use of TamSeal 800 sprayable membrane. As TamSeal 800 had not been used before in Singapore, Normet was required to go through a series of site trials and tests to validate the product system and convince the LTA that TamSeal 800 was the right solution.

All the parties discussed the implementation of TamSeal 800. Drawing 1 above illustrates the methods of using TamSeal 800 sprayable membrane in combination with Asiabuild’s Troseal Floroshield Reactive membrane. Detail 1 shows how TamSeal 800 was to be sprayed 1,000 mm above the base slab, with a 1,000 mm wide Troseal Floroshield Reactive membrane installed from the base slab. At the 300 mm overlap between the Troseal and TamSeal 800, another layer of TamSeal, about 500 mm wide, was to be sprayed to create a ‘sandwich’-like joint, reducing the chances of water seepage at the overlapping joints. The drawings above illustrate the three-arch tunnel before excavation of the central tunnel.

Detail 2 shows application methods using double layers of geotextile fleece, TamSeal 800, double-side self-adhesive tape, Troseal Floroshield membrane, TamSeal 800, etc. These methods are also designed to create a ‘sandwich’ to minimise water seepage.

Detail 3 shows the waterproofing methods after construction of the central tunnel. These involved bending the membrane onto the central tunnel as shown in Drawing 2. Once the bending was done, standard spraying of TamSeal 800 could then proceed. The method of application illustrated in Detail 3 creates a solution to minimise water seepage at the interface area.

Below are pictures of the mock-up for TamSeal 800 and Troseal showing the overlapping joint area.

Normet succeeded in providing the Mass Rapid Transit (MRT) with an alternative installation system. The conventional method of using preformed PVC sheet membranes using a loose lay technique makes rectification very hard when groundwater leakage occurs as there is no bond to prevent water paths.

In contrast, by using TamSeal 800 spray applied waterproofing, the membrane was fully bonded to the concrete, making focused rectification work far easier and more successful when there was localised leakage. Furthermore, a “reservoir” of groundwater builds up behind a sheet membrane and is ready to leak into the tunnel at any point. Use of TamSeal 800 prevents these reservoirs from forming because of the fully bonded system.