Micropiles and soil nails have been used to stabilise an embankment and support access structures at Exeter Central Station.
Contractor May Gurney Geotechnical installed the 300, 4m nails using a TEI mast mounted on a 16t excavator for client Bellway Homes Wessex Division.
Jubb Consulting carried out a slope stability assessment and chose Ischebeck Titan 30/16 selfdrilling soil nails fitted with expendable 75mm diameter clay cutting heads.
The heads have two holes through which grout is injected to first flush soil from the hole before grouting up around the bar.
After the nails were installed, May Gurney laid a Maccaferri 150mm open plastic-coated wire mesh that allows revegetation of the slope for further stability.
It also installed 36 vertical micropiles using the TEI mast, to support 150kN foundation loads for the seven footbridges and the main vehicle ramp to the station.
The same rig was used for the 8m piles and the soil nails, a cost-saving measure that added flexibility to the sequencing of the two stability methods.
The arrangement of the nails was designed to allow the layout to be adjusted on site during the course of the works.
This avoided damage to the canopies and roots of trees, most of which were subject to tree preservation orders.