Road Underpass | Hills Road Underpass, Cambridgeshire



Road Underpass utilising Leca.

Cambridgeshire County Council commissioned the £120 million Busway guided transport network to greatly improve passenger transport around the City and along the A14 corridor. The Hills Road Underpass, constructed with the aid of Leca® Lightweight Expanded Clay Aggregate, will be seen as a key element in the whole project.

Here an ordinary bus leaves the traditional highway driving directly onto the smooth, traffic-free, precast concrete beams. Guide wheels fitted to the front axle of the bus touch the raised verges of the rails and effectively steer the bus along the Busway.

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 carries a section of the access roadway.

To minimise the load on the roof section, Leca® Lightweight Expanded Clay 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 reported favourably on the use of Leca® Lightweight Expanded Clay Aggregate: “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® Lightweight Expanded Clay Aggregate 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 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® Lightweight Expanded Clay Aggregate was used at the Hills Road Underpass.