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The devastation of London's East End during the Second World War is still evident underground, as water main engineers are finding to their cost.

Sixty years after the obliteration of the East End during the Second World War, wartime rubble is slowing London's pipe renewal programme.

Thames Water began the work, aimed at reducing leakage, three years ago. Since then it has replaced more than 322km of Victorian water mains in 14 London boroughs at a cost of more than £115M. Plans are in place to invest more than £500M to upgrade a total of 1368km over the next four years.

Most distribution systems lose water. This can be attributed to several factors, but leakage is the primary cause and occurs in different components of the system, from transmission pipes to distribution pipes and joints and valves.

The situation is exacerbated by an ageing pipe network - half the pipes buried deep below London are more than 100 years old and a third are over 150 years old.

One of the areas where Thames Water has been replacing mains is Whitechapel, where high levels of leakage had been detected. Here, the problem of the network's age is compounded by wartime bombing rubble lying above. This has complicated many of the trenchless techniques used to relay pipes.

During and shortly after the war, the priority was to return things to normal as quickly as possible.

Destroyed buildings were bulldozed, fires were extinguished and people were allowed back into their homes and businesses without properly clearing the wreckage.

'There is so much rubble and debris in the ground that in some instances we are forced to dig up the street, ' says Thames Water project manager Andy Popple.

'This involves considerable slow hand digging to get rid of all the wreckage. In addition, when we take off the tarmac to access the pipes, we unearth the remains of cobbled streets which must be replaced before the tarmac can be relaid on top.' The company has found that pipe bursting is often impossible. This technique renews ageing mains by cracking the pipe, pushing it outwards and threading a new pipe through.

'With pipe bursting it is possible to replace the existing pipe with one of the same diameter or larger and the disruptions are much fewer, ' Popple says. 'However, in Whitechapel we advance a few metres and often come across unexpected complications that slow work down.' During the war, reconnecting the water was critical to supply fire engines, but often this was achieved in a haphazard manner. 'Because of the urgency, water pipes were just muddled together so there are surprise u-bends and 90° swan necks that are not indicated on any drawings, making it very difficult to lay a pipe down straight, ' he says.

London's clay foundations aggravate the ancient and inflexible cast iron pipe network. When the clay shrinks and expands it can crack the pipes or dislocate the joints and trigger leakage. In contrast, trenchless directional drilling exploits the malleable nature of clay to lay new pipes.

'In this instance, clay is our ally, ' says Popple. 'With existing pipes, acidic London clay is our enemy as it is eating at the pipes from outside in and when the clay freezes it causes fractures in the joints.

'However, by adding a high pressure water lubricant to the paddle we use in directional drilling, the clay becomes soft rather than collapsing in on itself and the paddle can be guided through the ground with ease to install a new pipe.' Navigation in the Whitechapel area is once again subject to interruption by wreckage and rubble.

'The plastic pipes that replace the old, cast iron pipes work in tandem with the clay and can expand or contract in keeping with the ground's seasonal variations, ' Popple explains.

'Most importantly, this is a quick, efficient method of relaying pipes that does not necessitate using the existing pipe, so customers can be simply transferred without suspending their water supply.' Historically, London was serviced by multiple water companies and Thames is encountering streets with numerous distribution pipes running along both sides of the road, which can all be merged together for improved ef'ciency. To further complicate matters, as Cable Street is the main link between the City and Canary Wharf, it is full of fibre optic cables.

In Whitechapel, where work began in January 2005, Thames Water is replacing 24km of old mains with 17.5km of new plastic pipes. The project is due to complete in August this year and it is hoped it will save 4.5M. l of water a day.

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