The main arterial road into Blackpool uses a 30 year old railway embankment which was constructed on soft alluvial soils. The embankment has been plagued with differential settlements for many years resulting in many closures for repairs, which creates major delays for the holidaymakers. Given that Blackpool’s economy is highly dependent on tourism, Blackpool Council approached Galliford Try and Coffey Geotechnics to develop a solution which would alleviate the problems.
The existing embankment (6-7 m high) consists mainly of soft to firm silty clay with a variable quantity of sand, gravel and boulders made up of a variety of lithologies. The natural soils below the embankments consist of up to 7m of soft to firm organic, gravelly clay which becomes stiffer with depth. At a depth of between 11m and 14m, medium dense sands are encountered which overlay, over consolidated stiff to very stiff clays.
The design involved removing the top 1.5m of the road embankment and then installing controlled modulus columns through the remaining embankment, through the underlying soft alluvial soils and toeing into the glacial soils below. The top 1.5m of the embankment was then reinstated using aggregate and geo grids to form a load distribution mattress over the CMC’s.