Hills Road - Cambridge

The £120 million Busway guided transport network now greatly improves passenger transport around the City and along the A14 corridor, the Hills Road Underpass, constructed with the aid of Leca® lightweight aggregate, is the key element in the whole project.

The new Hills Road Underpass for the Busway system had to be constructed to enable buses to travel from Cambridge Railway Station to Addenbrooke's Hospital and Trumpington Park & Ride in just eight minutes. The original bridge is a main artery into Cambridge and it was decided to keep it open to avoid long-term traffic chaos. The Underpass was created by piled walling and excavation. The cantilever roof section of the Underpass also has to carry a section of the access roadway. To minimise the load on the roof section, Leca® lightweight aggregate was selected for the backfill which, at the same time, provided the foundation material for the road surface. Craig Downing, materials engineer for main contractor BAM Nuttall on the Hills Road Underpass project for Cambridgeshire County Council, reports favourably on the use of Leca®: "This material is easy to handle, easy to compact even when wet and the speed of delivery pouring in a difficult access area helped us greatly with tight time schedules on site." The design was a joint venture between Parsons Brinckerhoff UK and Arup. Leca® is lightweight expanded clay formed by heating and firing natural glacial clay in a rotary kiln at up to 1150°C. This process transforms the clay into lightweight ceramic granules that have a hard ceramic shell and porous core. The material is extremely light with a bulk density of just 0.3 tonnes per cubic metre. More than 120m3 of Leca® was used at the Hills Road Underpass.