In Singapore the Public Utilities Board (PUB) is vested with the challenging task of maintaining the sewerage reticulation system which has its origin in colonial times. The Sewerage Department of the PUB identifies older sewers, restores their condition and keeps the health of the system in the pink to serve the increasing development in Singapore.

Sewer rehabilitation originally involved a large amount of excavation work and sewers were repaired mainly by the open trench method. The operation, while necessary, was time-consuming and often caused inconvenience to customers.

Today, the PUB uses a number of Trenchless Technologies in sewer rehabilitation work as they continue to maintain the 3,200 km of gravity sewers, 220 km of pumping mains and 130 pumping installations of the sewer reticulation system. Under ongoing sewer rehabilitation programs, a total of 790 km of sewers in various parts of Singapore will be rehabilitated.

The PUB is always on the lookout for new technologies that reduce inconvenience to customers. Pipe bursting and spiral wound lining are two such sewer rehabilitation technologies being utilised most recently.

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Spiral Wound Lining

The steel reinforced spiral wound PVC lining (SWL) is another method used for lining aging, corroded or deteriorated sewers.

A winding machine positioned in the base of an access chamber or manhole progressively winds a PVC strip in a spiral pattern forming a liner within the existing sewer.

The gaps between the newly formed liner and the existing pipe will be sealed with grout.

In comparison to conventional open trench method of pipe replacement, SWL system has several advantages that make it a rehabilitation option. The PUB has found that costs are reduced by as much as 30 per cent.

Consistent quality of work

The quality of work is not dependent on the standard of workmanship as the liner is completely installed by machine.

Less equipment needed

Less equipment is required to manage the flow in the sewers for the SWL system. The method can be used in any flow conditions in the sewers.

No need for excavation

The method uses the existing manhole without having to dig another pit.

Pipe Bursting-Trenchless Pipe Replacement

Pipe bursting involves a bursting tool replacing pipes by breaking them open from within by applying radial forces. A new pipe is simultaneously pulled in behind the bursting tool. An expander device on the bursting tool pushes the fragments of pipe into the surrounding ground. A thin walled sleeve is generally pulled into the newly formed bore directly behind the expander. This sleeve prevents the product pipe from being damaged by fragments of the old pipe in the surrounding ground.

The PUB has found a number of advantages in pipe-bursting;

Upsizing

One of the principal advantages of pipe bursting is its ability to increase pipe capacity by upsizing the original pipe diameter. This can be accomplished without excavation along the same alignment and grade of the original pipe.

Structural replacement

Pipe bursting provides total pipe replacement as a new pipe is structurally independent of the original pipe.

Rehabilitation time significantly reduced

Considerable time is saved compared to open trench methods with minimal excavation required to facilitate installation. As a result, the need for site reinstatement is reduced. The time to complete the entire installation decreases as much as 30 per cent.

Reduced impact on traffic

Pipe bursting reduces social costs associated with construction projects. Generally, when replacing pipes under a carriageway, only the localised area within a single lane is required to place the necessary equipment for the replacement job. Minimal traffic disruption will take place.