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Replacement and Rehabilitation Programme of Water Mains

Objective and Background

Objective:

To launch a comprehensive and systemic programme to replace or rehabilitate about 3 000 kilometres of aged water mains in 15 years to improve the condition of the water supply network so as to maintain a reasonable level of services to consumers.

Background:

Hong Kong's fresh water and salt water supplies are provided through a network of about 8 000 kilometres of water mains. Most of these water mains are underground. A substantial portion of the water mains was laid more than 30 years ago. They are progressively approaching the end of their service life and have become increasingly difficult and costly to maintain.

As a result of the ageing problem, we faced an increasing number of main burst and leakage cases causing inconvenience to the public and loss of precious water. The previous way of carrying out piecemeal and small-scale replacement works was not considered effective. Starting from 2000, we have implemented a comprehensive and cost-effective management plan for the water supply network. This involves the replacement and rehabilitation of some 3 000 kilometres of aged water mains in stages to rejuvenate the water supply network.

Staging of the Works

To tackle the problems arising from the ageing of water mains in a cost effective manner whilst minimising the effects on the general public, we need to replace and rehabilitate the aged water mains in stages in a systematic manner. Main considerations include the following -

  1. avoidance of unnecessary water supply disruption to consumers as a result of excessive amount of works,
  2. avoidance of unnecessary traffic disruption during construction as a result of excessive road opening works, and
  3. cost effectiveness of the works with priority given to water mains more susceptible to leakage and bursting.

The total estimated cost of the R&R programme is about HK$23.6 billion. A breakdown of estimated costs in individual stages of the R&R programme is presented below:-

Estimated Costs of R&R Works at Different Stages

The 15-year Replacement and Rehabilitation of Water Mains Programme is substantially completed in December 2015. The major remaining works are water mains connection works and road reinstatement works at present. Due to the constraints of the works implementation hours and the excavated area arising from the traffic situation and noise control requirements, some individual works in the project require a longer time for completion.

Replacement and Rehabilitation Methods

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
    Diagrammatic Illustration on Pipe Ramming
    Pipe Ramming Method in Progress
    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
    Pipe sleeve being jacked from the launching pit
    Tunnel Face Closed During non-Working Time
    Tunnel Face Closed During non-Working Time
    Excavation by Hand at Tunnel Face
    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
    Diagrammatic Illustration on Horizontal Directional Drill
    Horizontal Directional Drilling Machine
    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 (1)
    Polyethylene pipe being inserted into the old pipe
    Polyethylene pipe being inserted into the old pipe (2)
    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
    Pipe liner being inserted into the host pipe from ground level
    Launch Pit
    Launch Pit
    Liner Being Inverted out of Turning Equipment
    Liner Being Inverted out of Turning Equipment
    Pipe Prior to Lining
    Pipe Prior to Lining
    Lined Pipe
    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
    Diagrammatic Illustration on Pipe Bursting Method
    Bursting / Expanding Cone
    Bursting / Expanding Cone
    Pneumatically Powered Percussive Mole
    Pneumatically Powered Percussive Mole
    Pulling Rod
    Pulling Rod
    Broken Pipe
    Broken Pipe
     

Benefit from the Works

Upon the progressive completion of the Replacement and Rehabilitation of Water Mains Programme , together with the implementation of the active leakage control and pressure management on water mains, the water mains bursts drop significantly with leakage rates reduced at the same time. The disturbances due to disruption of traffic, loss of trade, inconvenience to the general public and disruption of water supply to consumers arising from main leaks and bursts have been minimised.

Nos. of Pipe Bursts and Leaks

Year No. of Bursts No. of Leaks
00/01 2,479 21,693
01/02 2,211 20,940
02/03 1,885 23,651
03/04 2,064 19,199
04/05 1,812 17,393
05/06 1,585 14,657
06/07 1,639 12,472
07/08 1,817 14,184
08/09 1,323 14,143
09/10 988 13,107
10/11 610 12,546
11/12 317 12,118
12/13 267 11,609
13/14 241 10,619
14/15 169 9,516
15/16 148 9,604
16/17 96 8,724

number of pipe bursts and leaks

Effects Arising from the Works

Effect on Traffic

During the construction stage, the contractors have been required to submit detailed temporary traffic management schemes using updated traffic counts and on-site trial runs for the works. The temporary traffic management schemes have to be approved by the relevant authorities prior to its implementation. It is expected that the traffic impact arising from the works can be kept within acceptable level by implementation of the temporary traffic management schemes during construction.

Besides, at locations where traffic impacts are significant, we would consider to use trenchless / minimum dig techniques to alleviate the traffic impact problems.

Effect on the Environment

We have undertaken an environmental review as part of the detailed design process. In the environmental review, noise, air quality, water quality, waste and ecological impacts have been assessed following with all relevant statutory requirements. Findings of the environmental review have been incorporated into the detailed design of the works as well as the construction works.

Noise, dust impacts and site run-off are the key environmental concerns. The general approach to the issues are described as follows -

  1. Noise

    We have included the requirements of Noise Control (Construction Work) Regulation into the works contracts to ensure that the statutory guidelines are complied with at all times. Monitoring will be carried out during construction to ensure that the sensitive receivers will not be adversely affected by the noise generated from the works.

  2. Dust

    We have included the requirements of Air Pollution Control (Construction Dust) Regulation and "Recommended Pollution Control Requirements for Construction Contracts" issued by Environmental Protection Department into the works contracts to ensure that the statutory guidelines are complied with at all times.

  3. Site Run-off

    All site run-off generated from the construction works will be treated in accordance with the Water Pollution Control Ordinance before discharge into the drainage systems to avoid contamination.

Effect on Consumers

Replacement and rehabilitation of water mains may lead to inconvenience to the general public due to the construction works. Apart from the inconvenience caused by the works, water supply to consumers will be also affected as the works will involve the disconnections from of the old pipelines and the making of new connections to the new pipelines.

In order to minimise the disruption of water supply to consumers, we are endeavour to keep the number of water supply suspensions and the period of each water supply suspension to a minimum by suitable planning of the works during and the construction of the works. In any case, we will limit the period of water supply suspension to within 8 hours.