In 1989 the British Geotechnical Society organised an evening meeting on soil nailing at the Institution of Civil Engineers in London.The meeting was titled 'Soil nailing - a solution looking for a problem', which neatly summed up UK experience with soil nailing at that time.
One of the first UK projects to eventually come through was a soil nailed wall at an independent family-run grocer, Jempsons, in Peasmarsh, East Sussex. Jempsons must have been a happy client, as a decade later it is expanding again, and once more soil nailing is providing the solution.
This time the family is looking to build a new store adjacent to the existing premises, which will be demolished and converted to parking.
Contractor Phi Group recently completed the earth retaining wall using its soil panel system in conjunction with solid threadbar soil nails.
Ground conditions at the site are Tunbridge Wells Sand overlying Wadhurst Clay, with a perched water table siting on the junction of the two.
Phi's in-house ground engineering division, installed Dywidag Gewi-steel solid soil nails to form a stable gravity block. Phi's Casagrande C6 drilled open hole, into which the nails were centralised by lantern spacers.
Nails were then grouted from the base using a tremie pipe.
Reinforced soil specialists are focusing on providing the horticultural environment necessary to establish a sound root base and sustainable growth. Phi's solution is its Soil Panel system which is designed to separate the growing medium from the heavily compacted reinforced soil block.
Soil Panel uses a back panel of galvanised mesh, secured against the face by bearing plates on the soil nails. Intersecting diaphragms are then clipped to the back panel to create individual cells with an additional layer of geotextile lined mesh, secured at the front.
Resulting cells are carefully filled with a seeded and fertilised top soil to promote an environment that is compatible to plant growth.
In advance of the main contract, Phi used pull-out tests to establish design parameters.
Tests comprised short term pull out tests for the sand, and short and long term pull out tests for the clay, thereby enabling an efficient nailing solution to be proposed.
Terram-geotextile wrapped perforated pipes formed inclined adit drains to drain the perched water tables. These were installed up through the Wadhurst Clay and into the base of the overlying sand.