BLANKETING THE SURFACE WATER

This article describes the construction of the new bridge being built at Guyhirn in Cambridgeshire, taking the A47 Leicester to Yarmouth trunk road over the river Nene. The new bridge and associated road works are being built on a layer of alluvial fen silts and clays between 11 m and 12 m deep. 165000 m of vertical drainage was installed by contractor Spencer King's Geotechnical Division, to overcome the problem of slow natural settlement of the soil under the loading of the bridge and roadworks. As the drainage forces water out, ground settlement occurs. Together with the vertical drainage, Spencer King is also installing a network of inclinometers and piezometers, to monitor the movement within the soil and the pressure of the water trapped in the material. 36000 cu m of clay is being used to construct the embankments and two bridge approaches. The project began in August 1989 and is expected to be completed in autumn 1990. (TRRL)