The solution involved a two stage process. Stage one involved the placement of vertical drains beneath the proposed embankments either side of the new bridge. The vertical drains were installed through the alluvium soils into the sands and gravels at depths of approximately 8.0 to 10.0m.
Following installation of the vertical drains, the first phase of the embankment construction was initiated. This first phase embankment was built to heights of up to 5.5m and extended a significant distance beyond the proposed footprint of the road. The first phase embankment was monitored until the rates of settlements reached an agreed rate.
After 12 months of surcharge, the rate of settlement reached an acceptable rate, following which CMC’s were installed to depths of 15m, beneath the footprint of the second phase of the embankment construction. Following installation of CMC’s the second phase embankment construction commenced up to heights of up to 2.5m.