A47 Thorney Bypass, Ground Stabilisation Solution
A47 Thorney Bypass, Cambridgeshire Highways Agency WS Atkins Birse Civil Engineering E’GRID 30/30™ & MultiTrack 1000™ 200,000 m²
The A47 is a primary trunk road linking Birmingham and the midlands with Great Yarmouth in Norfolk. Its route through Thorney, Cambridgeshire had been a historic ‘bottleneck’ for many years so a bypass was needed.
With the bypass comprising over 14 km of new dual carriageway built over marshland it was always going to require the use of geosynthetics to provide the client with the optimum design solution.
The presence of very soft ground conditions required the use of an underlying geotextile to provide separation and filtration. It was important that a high elongation non-woven geotextile was used to ensure that it would stretch, without bursting, around the granular stone above it. Multitrack 1000 was chosen for this purpose.
To provide ground stabilisation at the base of the highway, and further separation of the granular fill from the underlying marshland, a layer of E’Grid 3030 biaxial geogrid was placed on top of the Multitrack 1000 geotextile.
The E’Grid 3030, installed across the width of the carriageway, provided continuous strength in the main load carrying direction. Product continuity along the length of the carriageway was provided via a 300mm overlap, secured during the construction phrase with plastic cable ties.
In total, over 400,000m2 of geosynthetics were installed on this project.
E’Grid biaxial grids are produced from 100% virgin polypropylene on the world’s first fully integrated geogrid production line. They are produced by punching and stretching high quality punched polymer sheets under closely controlled factory conditions. The resulting E’GRID biaxial geogrid has square apertures, high tensile strength and an optimised geometry of nodes and ribs that maximises interlock with the soil.
Due to the high tensile stiffness of E’Grid biaxial geogrids, working loads are developed at very low levels of strain in the construction. This, together with the fact, that the overlying granular material partially penetrates and projects through the apertures to create a positive interlock with the underlying surface, ensures maximum performance is obtained from the reinforcement/ stabilisation.