The earthwork which supports the northbound A419 dual carriageway, just north of Swindon, on its approach to the A361 Highworth Road over-bridge, comprises a 6m high embankment of Oxford clay at an angle of 26° within which a 15m wide failure had developed from the crest of the slope to approximately 2.0m from the toe, thus undermining the vehicle restraint system over a length of 12m. Previous remediation with granular replacement had proved unsuccessful.

The alternative to the EKG system under consideration comprised excavation and rebuild using the excavated material as fill for reinforced soil. This was not favoured owing to access restrictions and the impact of extensive earthworks using large plant and the associated level of traffic management that would have been required.

The design comprised:

• 28 anodes ranging from 4.5 – 7.5m
• 18 cathodes ranging from 6.0 – 9.0m.

The construction sequence comprised:

• Strim vegetation and remove fence
• Deliver plant including DC power supply, AC generator, fuel tank, temporary storage for EKG materials – 1 day
• Install electrodes; 3 days (2 man crew) with a small, slope climbing rig; zero earthmoving
• Connect electrodes; 2 days (2 man team)
• Active treatment of 6 weeks with weekly visits for re-fuelling and data collection.

After the completion of the active treatment, the site was decommissioned immediately.

Decommissioning summary:

• Remove plant and electrical materials- 4 hours
• Installation of grout, tendons and faceplates – 3 hours (3 man team)

The delivered benefits of the EKG system included:

• The slope was remediated in its existing condition, requiring no earthworks and produced zero waste
• During the construction programme which totalled 58 days the total personnel requirement was only 33 days on site
• Small construction plant allowed for easy access
• The total cost for the scheme delivered savings over the alternatives under consideration
• Traffic management was limited to a closure of a footpath for the programme and temporary diversion to a footpath for the delivery and collection of items of plant
• The EKG system embodied 6.54T CO₂ representing a 35% reduction compared to projections for the reinforced soil alternative.

On this site the installation of 46 driven and bored electrodes provided detailed information which confirmed the anticipated ground conditions.

This in turn permitted redesign of the array and significant savings due to fewer installations, less cable and lower overall fuel consumption. As such the EKG system is adaptable and responsive to the observational method.