Fill and Monitor Solution to Construct Highway Embankment

On this project, part of the road is carried on a 5m high embankment which overlies a historical railway cutting. The railway cutting was up to 9.5 m deep and is infilled with landfill material, placed predominantly during the 1970s. Ground investigation was carried out to determine the composition of the landfill material, which generally comprised a clay/sand matrix with relatively thin layers of non-soil materials. A risk-based approach was used to compare the relative merits and risks associated with various forms of ground treatment. The preferred approach was to construct the embankment on untreated landfill material and to use a system of monitoring to prove when settlement was complete, resulting in the least-time/cost, least-carbon option.

Comprehensive ground investigation and adopting a risk-based approach to evaluate treatment options allowed the ‘fill and monitor’ solution to be chosen, with significant savings relative to more invasive options. Settlement was monitored using a combination of optical surveying of rod and plate installations, optical monitoring of survey points and vibrating wire settlement gauges.

The project team has submitted a paper to the 5th International Seminar on Earthworks in Europe, which provides a case history of this observational approach to manage settlement risk of landfill material, to provide a reference which will be useful for comparison where similar low cost, low carbon approaches are considered on other schemes in the future.