Water Main Replacement Methods

The conventional method to replace aged water mains is to lay new water mains alongside the existing water mains using trench opening method. Upon completion of making connections to the new water mains, the existing water mains will be abandoned. As this method will involve road opening for the whole section of the water main, the method will be generally acceptable when the traffic and environmental impacts arising from the works are not serious and when the underground utilities present are not congested.

At locations where traffic and environmental impacts are causing concerns, our intention is to use trenchless techniques. These techniques are sometimes referred to as 'minimum dig' or 'reduced dig' techniques to accurately indicate the methods still require the opening of pits.

Trenchless replacement techniques involve the pre-drilling of a hole of suitable diameter and the insertion of a pipeline along the pre-drilled hole. Upon completion of making connections to the new water mains, the existing water mains will be abandoned. As the techniques need to avoid the already congested underground utilities, the pipelines will be laid deep underground which will lead to operation and maintenance problems. These replacement techniques will be limited to small areas with traffic and environmental problems. The main techniques are described below -

	(1)	Pipe Ramming
		This method involves the driving of a pipe sleeve from the launching pit using a pneumatic ramming machine to the receiving pit. The soil inside the pipe sleeve is removed and a new pipeline is then inserted into the pipe sleeve. Size Range: Pipes of diameter from 150 mm to 1200 mm Diagrammatic Illustration on Pipe Ramming Pipe Ramming Method in Progress
	(2)	Pipe Jacking
		This method involves the jacking of a pipe sleeve from the launching pit using a hydraulic jacking machine to the receiving pit. The soil inside the pipe sleeve is removed and then a new pipeline is inserted into the pipe sleeve. Size Range: Pipes of diameter over 900 mm Pipe sleeve being jacked from the launching pit Tunnel Face Closed During non-Working Time Excavation by Hand at Tunnel Face
	(3)	Horizontal Directional Drilling
		This method is suitable at busy road junctions or river crossings. In this method a pilot hole is drilled along a designed profile using a drilling rig. The pilot hole is then enlarged to a suitable diameter by 'prereaming' the hole successively to a larger diameter. Once the drilled hole is enlarged, the new pipeline is then installed by pulling a prefabricated pipe through the drilled hole. Size Range: Pipes of diameter from 300 mm to 1200 mm Diagrammatic Illustration on Horizontal Directional Drill Horizontal Directional Drilling Machine

Water Mains Rehabilitation Methods

Rehabilitation methods are generally classified as trenchless methods (sometimes referred to as 'minimum dig' or 'reduced dig' methods.) In these techniques, a new pipe is launched from a 'launching pit' and travels along the existing pipe route to a 'receiving pit'. Under ideal situation, a pipe can travel up to about 100 metres to 200 metres. In practice, bends in the existing water mains would shorten the length of the water main to be rehabilitated. In general, rehabilitation methods are classified as follows -

	(1)	Close Fit Lining Method
		Close fit lining technique involves the insertion of a temporarily reduced diameter or re-shaped polyethylene pipe as a lining into an existing water main. The inserted pipe will be reverted to its original size on completion of the insertion process and form a lining in close contact with the existing pipe barrel. This technique relies on the flexibility and toughness of polyethylene pipe to revert to its original size after being deformed. Polyethylene pipe being inserted into the old pipe
	(2)	Cured in Place Pipe Method
		This method involves the insertion of a polyester woven liner with epoxy resin by inversion (turning inside out) into the existing pipe. The liner is bonded to the host pipe to form a close -fit pipe after hardening of the resin. Size Range: Pipes of diameter 150 mm to 1000 mm Pipe liner being inserted into the host pipe from ground level Launch Pit Liner Being Inverted out of Turning Equipment Pipe Prior to Lining Lined Pipe
	(3)	Pipe Bursting Method
		In pipe bursting, a pneumatic or hydraulic bursting tool is forced through the existing water main causing it to burst. Fragments of the existing water mains are pushed into the surrounding soil by a spreader and a new pipe is installed in the vacated space. The new pipe may, if required, be slightly larger than the old pipe. Size Range: Pipes of diameter 50 mm to 500 mm Diagrammatic Illustration on Pipe Bursting Method Bursting / Expanding Cone Pneumatically Powered Percussive Mole Pulling Rod Broken Pipe