Singapore's Public Utilities Board (PUB) is vested with the challenging task of maintaining the sewerage reticulation system in Singapore. The system 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, the process of restoring old sewers involved large amount of excavation work in the eighties. Sewers were rectified mainly by the open trench method. The operation while necessary is time-consuming and often caused inconvenience to customers. Today, the PUB uses a number of "trenchless technologies" in sewer rehabilitation work to maintain the 3200 km of gravity sewers, 220 km of pumping mains and 130 pumping installations of the sewer reticulation system. Under ongoing sewer rehabilitation programmes, a total of 790km 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.
Using the two methods, we achieve cost savings from reducing the expanse of excavation work and extensive cable detection work carried out to mark out the cable locations. Fewer trial holes need to be dug before actual excavation work begins. With fewer holes on the roads, traffic disruption and noise pollution is minimised.
Pipe Bursting-Trenchless Pipe Replacement
Pipe bursting is a trenchless method of construction used to rectify underground pipelines. A bursting tool replaces 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.
Advantages
In comparison to conventional open trench method of pipe replacement, pipe bursting has several advantages that make it an economical option as costs is reduced by as much as 40 per cent.
1.
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.
2.
Structural replacement
Pipe bursting provides total pipe replacement as a new pipe is structurally independent of the original pipe.
3.
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.
4.
Reduced impact on traffic
Pipe bursting reduces social costs associated with construction projects. Generally, when replacing pipes under a carriageway, only the localized area within a single lane is required to place the necessary equipment for the replacement job. Minimal traffic disruption will take place.
Sewer Lining by Steel Reinforced Spiral Wound PVC Lining (SWL)
SWL system
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 wound 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.
Advantages
In comparison to conventional open trench method of pipe replacement, SWL system has several advantages that make it a rehabilitation option. Costs are reduced by as much as 30 per cent.
1.
Consistent quality of work
The quality of work is not dependant on the standard of workmanship as the liner is completely installed by machine.
2.
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.
3.
No need for excavation
The method uses the existing manhole without having to dig another pit.
FROM:
Nursing sewers back to health, 17 December 2003
http://www.pub.gov.sg/mpublications/Pages/PressReleases.aspx