Project Briefing

Microtunnelling & Shaft Sinking in Kent

Jackson Civils

Locaton: Westwood Cross Relief Road

Technique: Microtunnelling & Shaft sinking

Main Contractor: Jackson Civils

Working in hard ground, Perco is using microtunnelling to install over 0.5km of sewers for a large and prestigious project on the Isle of Thanet in Kent. Perco’s engineers also sank eight 3 metre diameter caisson shafts.

The 20-week job is part of the development of Eurokent Business Park, between Margate and Ramsgate, to the south of Westwood Cross. The business park already has manufacturing sites and offices and plans are in place for a £25 million leisure development, including a multiplex cinema, health and fitness centre, restaurant and other amenities.

Together with a new housing project at Westwood Cross, the expansion of the business and leisure areas called for upgrading of the public sewer, which was built in 1974 and at 225mm diameter, has been operating at full capacity. Perco is installing a new 300mm clayware sewer alongside the existing one.

Main contractor, Jackson Civils, is responsible for the facilitating works and construction of a £4m public access road for Kent County Council. Project Manager for Jackson Civils, Alan Breck comments: ‘This is Perco’s first project with us. With one exception each of the shots is roughly 85m in length and while a problem was encountered early on, this was overcome and the work is going well.’

Permanently on site for Perco is Site Agent Sam Burgoine: ‘The ground conditions are consistently hard between 7m and 10m below ground level, at approximately SPT 65. This was too hard to consider auger boring. Microtunnelling is the right method for the job and we are now into our fifth of seven shots totalling 520m.’

Using a 300mm Iseki Unclemole, the Perco team is installing Naylor Denlock clay pipe in two metre sections.

The new sewer is being constructed on former farmland, which often means that open cut working would be acceptable. However, as The Eurokent Business Park and other sites in the area are already occupied and have service roads, a trenchless construction method was favoured to avoid disruption.

Perco is sinking eight 3 metre diameter caisson shafts as part of the project. These form the 10m-deep launch and target shafts for the microtunnelling and pipe jacking operations, which will also provide access manholes for the new sewer.