Grimshaw Group: A specialist civil engineering company providing quality construction services throughout Gloucestershire, Herefordshire, Worcestershire, Oxfordshire and Wiltshire, including Bristol, Gloucester, Birmingham and Oxford.

Civils specialist clears hurdles with precast solutions.

It is unusual for a contractor to be faced with the task of juggling a watercourse, a multi-million pound business, millions of poundsworth of racetrack and horsepower, and have to take into consideration residential housing in one project.

Nevertheless, this was the situation that presented itself to Cheltenham-based civil engineering specialist Grimshaw Kinnear when it was contracted to construct a number of phases on the Prestbury Flood Relief Scheme for Cheltenham Borough Council.
 
   


Cheltenham Racecourse, home of the world famous Gold Cup horse race, the pinnacle of National Hunt racing, is situated in the village of Prestbury just outside Cheltenham.

Grimshaw, which has been the preferred contractor for maintenance and projects at the racecourse for over 30 years, is used to putting its innovative skills into practice and taking on projects which are out of the ordinary.

Box Culverts
The first hurdle to confront was Hyde Brook which runs through Prestbury village and the racecourse. The brook was frequently rising beyond its banks causing damage to the surrounding areas.

Although the racecourse itself wasn’t suffering from the floods, the brook was in the path of the necessary works. As new box culverts were needed under the racing turf to improve the water flow, it was vital to negotiate the problem posed by the brook.

It was necessary for Grimshaw to devise a method of construction for the three new culverts working in narrow corridors across the course.

The work had to be completed and the racing turf restored in just one summer season between the famous National Hunt Festival and the start of the next racing season in October. At the height of the project up to 14 precast culvert units, each weighing 5.5 tonnes, were being installed per ten hour shift.

Project Logistics
The project was divided into three phrases working upstream, focusing first on the racecourse and then on the residential area. The first two phases of the project involved fitting the culverts over a watercourse within the grounds of the racecourse.

This work, although vital for Prestbury, was a huge undertaking for the racecourse and potentially disruptive, as managing director of Cheltenham

Racecourse Edward Gillespie explains: “The racecourse needed to be dug up in three places to accommodate the culverts.

Grimshaw excavated vast, 5m–wide trenches which crossed the racecourse in two places. For any venue this is a huge undertaking, but for a racing track with infrastructure including grandstands worth millions of pounds, precision was vital.

“The turf and sub-soil on the racetrack needed to be replaced almost exactly. Racehorses’ hooves impact up to six inches beneath the turf and it was extremely important that the sub-soil was a facsimile of what we had before.

With horses of the caliber we get at Cheltenham we couldn’t afford to have any misplaced soil, not only in terms of quality of racing but more importantly to eliminate any possibility of injury.”

Moving on to the residential phase of the project presented a new set of challenges.

The residents had already had to tolerate having their properties flooded so it was important to cause minimum disruption. A solution was required that would be effective for the foreseeable future.

Cut-and-Cover Method
The specified Hanson FC precast concrete culverts, 1.6m high and 2.5m wide, were put into position under the brook using crawler cranes, hydraulic excavators and a monorail system. To ensure that the culverts were fitted in the correct position with the maximum benefit, a ‘cut-and-cover’ method was used. The foundations of houses in the vicinity were constantly monitored.

Conclusion
Once the new culverts had been installed, Grimshaw ran a series of sample tests to ensure that soil was reinstated to its original condition and that the culverts would have the desired effect. The Prestbury Flood Relief Scheme took over three years to complete and the budget for the entire scheme was £650,000.

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