A12 Marshland Road - Great Yarmouth
A roundabout was extended from one lane to two to accommodate traffic using a new Tesco supermarket on the outskirts of Great Yarmouth, Norfolk. The challenge for engineers was that the coastal location is low lying, its condition is naturally marshy and the water table rises and falls with the tides. The roundabout sub-base and pavement were extended onto the existing verge and a new embankment was built using Leca®. The contractor was Jackson Civil Engineering, working on the adopted roads, on behalf of R G Carters (Builders) Limited and Tesco Stores Limited. Civil engineering designer, Boreham Consulting Engineers Limited, had specified the use of a lightweight aggregate to minimise differential settlement. Jacksons cut away the existing embankment at a right angle to the line of the new outside edge of the carriageway. Services were then installed including 14' deep wick drains and a drainage blanket. The Leca®, in conjunction with the wick drains, accelerated settlement to completion within six months, compared to an expected two to three years using conventional fill. The Leca® was tipped over a geotextile membrane and tracked in place using a mini excavator to minimise any surface movement. The geotextile was then rolled over the Leca®, creating a 'sausage', preventing migration of the material. This was then soiled and seeded. A total of 1,500m3 of Leca® was used on the Gapton Hall roundabout.