Capital investment

If you try to fix a leaky Victorian pipe in London, the chances are you will cause another leak. Trenchless technology is the way forward. We look at the progress made by one of the major contractors working in the city, Clancy Docwra.

With the South-east carrying an increasingly higher population density, demand rates for water per person are on the rise. And, with further developments planned across the region, this can only increase. So, for Thames Water, control of leakage across the distribution network is as much a major priority as its raw water sources.

For decades, with the water companies in public hands, there was a significant acknowledged shortfall in investment in the water distribution network. This was the reasoning behind privatisation of the water industry at the end of the 1980s, in that it was believed that much of this under-investment could be addressed through new investment by privatised water companies.

But, with the AMP pricing schemes established along with privatisation, a balance has had to be struck. This is between the prices paid by water customers, and the investment that could be made using this income by the water company. And water company investors’ interests must be taken into account.

Over the past decade or so, the UK has had occasions when the lack of rain has led to calls for reduced leakage. Unfortunately, these calls often do not account for practical and engineering circumstance. Fixing the leaks is not as easy as it sounds.

Much of the distribution system operated by Thames Water comprises cast-iron water mains beneath heavily trafficked and highly populated streets across large areas of the South-east, in particular central London.

Many of these mains were installed by Victorian engineers and are between 80 and 150 years old.

The leakage problem associated with these mains is also not specific. There are instances where major leaks occur due to full-bore fractures or pipe joint failures that make themselves obvious with eruption of water at the surface. And often the news headlines.

There is a significant amount of leakage that is due simply to the ageing process of the pipe with small, almost pinhole, leakage amounts that are almost impossible to locate and repair across the tens of thousands of kilometres of pipeline in the area.

Leakage rate

District monitoring and flow measurement shows where this type of leakage is most prevalent and when such a section of pipeline is highlighted the only real alternative is to refurbish or replace the pipe as a whole.

Thames Water, over the next five years, is investing £500M-plus to replace ageing mains. But, as leaking pipe is replaced in one area, pressure can increase – which can cause others to leak. This leads to new leakage on the remaining old pipe sections. This is why simply digging down to repair individual leaks is not effective.

It also means that a significant amount of work will need to be completed before any noticeable change in leakage rate occurs.

So, with a network of water supply pipe totalling around 30,000km in its area of operation, this is a difficult position to achieve. But, as part of the major water main replacement investment programme, more than 200km of old cast-iron main was replaced with new MDPE pipe in the past three years.

In central London, Thames Water currently has four of the UK’s major civil-engineering contractors constantly working on water main replacement – the Victorian Mains Replacement (VMR) Project. These contractors have work programmes covering mains replacement, over the current five-year AMP 4 period, totalling several hundreds of kilometres of pipeline.

One of these contractors is Clancy Docwra, which is replacing 360km of pipeline over the period. This work is designed to reduce leakage in the Thames Water system in north-east London and the City by 30M-40Ml/day.

The work over this period is worth £125M on this project area alone.

Given the high population density and heavy traffic in these parts of London, one of the main thrusts in planning the work schedules has been how to minimise the impact on everyday life while achieving the installation targets set by the contract. The option to use trenchless technologies has always been a significant part of the planning process, with the various options available being used regularly.

As well as traditional and trenching machine-based open cut work, Clancy has used horizontal directional drilling, pipe bursting, pilot/auger boring (small-bore micro-tunnelling) and insertion (sliplining a new MDPE pipe into the existing main).

About half of the 180.2km of work completed has been achieved using open-cut techniques, with 52% of the new installations being made using trenchless technologies in one form or another.

With only a small amount of auger boring (55.5m) and a limited amount (8,872m) of insertion work having been completed, most (more than 39% or 70.8km) of the trenchless installation work has been done using horizontal directional drilling. Clancy has worked with its sub-contractor, Mark II Drilling.

The replacement projects were not made any easier by variations in ground conditions. In most places, as expected, Clancy encountered typical London clays along with some ballast. But some areas also included varying degrees of rubble, believed to be remains of bomb damage from World War II.

Extensive underground surveys have been carried out by Clancy’s professional partner, CTS Cable Tracing Services.

This is always done before final planning and work programme composition, to enable Clancy’s engineers the facility to choose the right technique to be used in the right place.

More recently, Clancy has invested in new pipe-bursting equipment in the form of an Earth Tool/Hammerhead-manufactured Hydroburst HB5058 pipe-bursting rig, supplied by Hammerhead’s UK distributor U Mole.

All of the pipe-bursting work being undertaken by Clancy’s personnel, with training provided by U Mole.

The Hammerhead HB5058 unit is a static rod-based pipe bursting system, which uses an optional 15.1kW Kubota-driven power pack to provide hydraulic power for the pipe burster. The HB5058 unit is a 1,650mm-long by 600mm-wide by 341mm-deep frame housing the hydraulically driven rod puller.

Designed for the replacement of both water and gas mains made of friable materials, the rod puller generates up to 50 tonnes of pulling force. This is transferred through an easy-clean jaw arrangement, using 50mm-diameter, 1m-long pulling rods. The HB5058 can burst pipes of between 76mm and 255mm diameter over up to 100m lengths. This means that from a central bursting pit, up to 200m of replacement pipe can be installed from a single set up.

The Hydroburst HB5058 has pin-joint tooling for easy connection as well as robust construction on a unit, which, the company says, is easy to operate.

To date, just 7% of the total replacement work has been completed using pipe bursting (12.6km). Jeff Booker, project director for Clancy Docwra, says: “The early successes to date of the pipe-bursting system we have purchased leads me to believe that, given the right circumstances and ground conditions, we will see a very significant increase in its use on the VMR project.”

A burst of pace

While pipe bursting is now being used regularly across the VMR project sections being completed by Clancy, one of the most recent sections to be pipe burst was on Sandringham Road, London E8. A 50m bursting run was completed in under an hour from the start of the pull-in to the new pipe entering the start pit.

A further 100m of bursting was expected to be completed during the course of the same week. The existing pipe on Sandringham Road was a 100mm-diameter cast-iron pipe with numerous ductile repair collars.

Roger Thatcher, project manager says: “The HB5058 is very simple and easy to use, and it has the power we need to get the job done. It has also been very reliable.

The only problem we have had is that early on in the programme we had not worked out that it is often best to fit the ductile cutter on every job and occasionally we had to dig down to release the head when it became stuck on a repair collar. We now put the ductile rig on every time and have had no such trouble since.”

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