Articles & Case Studies


Posted: Thursday 6th May 2010

The Royal Train Yard at Wolverton Rail Works in Milton Keynes was for many years the home of the Royal Train when not in use by members of the Royal Family. Subsequent to the transfer of the Royal Train to a new home, the old Royal Train Yard building remained empty for a number of years. This was until housing developer Willmott Dixon took possession of the site to create 300 new homes. The project saw Willmott Dixon Construction division combining forces with Willmott Dixon Housing to tackle a very complex refurbishment of the 200 year-old building.


During the redevelopment work there was a requirement to stabilise an area of potentially unstable ground under the existing building which investigations showed carried a 900 mm diameter surface water sewer. The sewer ran at a depth of 14 m below the historic Grade II listed building and the Grand Union Canal connection London to Birmingham. The sewer was the responsibility of Anglian Water.

Historical drawings showed the sewer under the area in question as running in a straight line between two manholes for a distance of just over 100 m. Armed with this information of the location of the sewer, Willmott Dixon’s engineers drilled a bore hole which was pumped full of concrete to stabilise the ground below. The information from the records gave the contractor confidence that the bore hole was a good distance away from the course of the sewer. In the event, the drawing was found not to be complete. The sewer had in fact been constructed, not in a straight line as shown on the drawing, but as a long slow bend with part of its course running directly below where the bore hole operation had taken place. This meant that the bore hole had been drilled directly into the sewer which had subsequently been completely filled with concrete.

Once aware of the situation Willmott Dixon, with Anglian Water’s approval, attempted to remove the concrete using high pressure jetting. Unfortunately this proved ineffective.

Subsequent attempts were made to remove the concrete using man-entry methods and water lances. Whilst this achieved the removal of some 2 m of concrete, the operation was abandoned on Health and Safety grounds because the pipe structure was compromised by cracking found near to where it was believed the bore hole had passed through it.


With the development works on the property coming to an end, the urgency to find a solution to the problems in the surface water sewer grew. This led Anglian Water’s Steve Jones, the company’s Asset Engineering Manager, along with Andy Buckley, Civil Asset Engineer, who oversaw the project, to approach specialist underground construction contractor OnSite to see if the company’s ‘No-Dig’ expertise could be utilised in resolving this difficult problem.

OnSite initially proposed to use its high-specification robot cutter unit to grind out the concrete. Initial attempts with this system progressed very slowly. The company then came up with a unique and safe method of man entry working which would enable crews to work within the pipe whilst remaining fully protected during the cutting operations.

The method involved installing a series of structural CIPP repair patches inside the pipe up to the face of the concrete. The concrete excavation team could then work safely within the ‘patched’, and therefore supported, area of the pipe whilst further concrete was removed. A new patch was installed after every 0.5 m of concrete was removed, enabling safe working to continue.

As the operation progressed a constant appraisal of procedures was carried out with new ideas and suggestions being put forward all the time. Such suggestions included the installation of a temporary support heading where the concrete had been poured into the pipe. After just 7 days the teams working within the pipe had completely removed the 8 m long concrete obstruction.

Subsequently, and to ensure the long term structural integrity of the pipe particularly around the damaged area caused by the bore hole, Anglian Water accepted OnSite’s proposal to fully line the damaged area using its structural Premier-Pipe CIPP lining system.

Whilst an alternative GRP lining method had been considered it was ultimately rejected by Anglian Water on the grounds that, once installed, the sewer pipe flow capacity could be insufficient with the loss of so much cross sectional area, which concerned Anglian Water’s engineers.


Premier-Pipe is a cured in place pipe (CIPP) renovation process which is installed without the need for costly and disruptive excavation. The linings are individually manufactured to suit the dimensions of the pipes to be lined, the lining thickness being determined by individual design requirements. The lining tube is made of polyester felt with an outer coating of polyurethane. The tube is impregnated thoroughly with a liquid resin chosen to suit the working environment of the pipe. Once impregnated with resin, the Premier-Pipe is installed using the inversion method and cured with hot water.

Normally installed from manhole to manhole, the installation process comprises inversion of the liner into the host pipeline using water pressure from a scaffold tower. Once inversion is completed the water is circulated through a boiler to heat it to a temperature which cures the resin. Once cured the liner is an independent structural pipe-within-a-pipe which operates without residual strength from the host pipe.

The Patch Repair liners used to create the safe working environment within the host pipe during the concrete excavation works was a structural design. In this instance, the resin impregnated felt liner patch is loaded around an inflatable bladder which is positioned inside the pipe over the site where it is to be installed. The bladder is inflated with compressed air to push the liner against the inner pipe wall. In this instance an ambient cure resin is utilised which does not require heating to achieve the final cured condition. Once curing is completed the bladder is deflated and removed, leaving the patch in position within the pipe.


For the final lining operation, instead of lining the sewer from manhole to manhole, OnSite decided to install a structural ‘blind shot’ lining. As access to the upstream manhole was located on Network Rail property, which in a previous life had been an old asbestos dump, the potential access and Health & Safety issues meant that it was felt that all work should be carried out only from the downstream manhole which was located on the developer’s property.

The liner was therefore installed from the down stream manhole in an upstream direction to a point ending some 6 m passed the damaged area of the pipe where the pipe was known to be undamaged. This was achieved by using a calibration hose of the correct predetermined length to invert the liner into position and hold it in place during the cure process. The hot water circulation required to achieve the cure of the liner was done using the water within the inversion calibration hose. Once curing was complete, the inversion water was pumped out and the calibration hose was recovered to the downstream manhole and removed, leaving the liner installed within the host pipe.

Harry Robinson, Site Manager for Willmott Dixon remarked: “Ultimately this contract was a complete success and removed a major head ache for us. Without using trenchless techniques in the way we did through OnSite one of very few alternative options considered would have been to construct a new sewer around the building under a very busy single tracked, 2-way traffic-light controlled tunnel which carried across it the Grand Union Canal. However, because of the confined space and other services which were already laid within the road it was just not feasible. Overall we were extremely pleased with OnSite’s professional approach and its site team’s safe delivery of the project they said they would, including coming in on the agreed budget. This is one occasion when there really was only one solution.”

Mr Robinson continued: “If we had to risk boring a new pipe under the main building itself through unknown ground conditions where we could easily have hit a brick support that formed part of the foundations as well as having to pass through contaminated Network Rail land, such a project could have been nightmare. The costs would also have run into hundreds of thousands of pounds as well as creating a delay of the sites final handover to our customer.”

For OnSite, Bryan Lord Business Development Manager said: “Using our experience in trenchless technology and confined space working we were able to provide Willmott Dixon with a practical solution to the problems encountered on the surface water sewer at the Royal Train Yard development. Whilst not an easy task, our team called on several years of combined experience to bring together a solution which utilised a number of different techniques, some in ways not normally associated with the product used. Our solution also enabled the developer to minimise the cost implications of the problem whilst meeting its hand-over deadlines, something that may not otherwise have been possible.”

Read the magazine online

August 2021

About the magazine »
Magazine archive »


Information for advertisers »

Huber Harvey Communications buttonwood marketing Water Aid Cranfield University British Water Pulsar Button June 13 wateractive
Pulsar New Banner