We were invited to provide design and project management for a gravity crib wall at our client Millgate Homes site in Trevereux Hill, Oxted. Due to the site topography, the crib wall was located immediately in front of the toe of a previously excavated embankment. Therefore the void between the back of the crib and the existing bank needed to be backfilled during construction.
Our experienced engineers decided to install a reinforced soil / crib hybrid system using reinforcing grids connected to the rear of the crib and tensioned within the backfill zone, this option made full use of the fill material placed and compacted as a reinforced soil mass and also allowed the thickness of the crib wall section to be reduced.
Whilst we were working on the reinforced crib wall a question was raised regarding the long term stability of the made ground slopes forming a level garden for the plot at the other end of the site.
We commissioned and managed a site survey and slope specific soils investigation including window sampling boreholes in order to determine the interface between the made and natural ground, allowing the new ground profile and geology to be modelled and an overall stability analysis to be carried out.
It was identified that there was potential instability where the new made ground slope intersected the existing poorer sandy clay ground and a remedial scheme was designed using soil nails and mesh to intersect potential slip planes.
A single/double row of approximately 90 soil nails, each 6m long, were installed in the bank with over 400m2 of rock mesh placed on the slope and attached to the soil nails using plates and captive nuts. The nails were then cut off flush to the top of the nuts to enable the whole reinforced area to be covered by a layer of suitable granular backfill and topsoil to promote future vegetative growth and blend in to the natural bank.
The whole site operation, including the formation of a working platform which had to be set into the steepest part of the slope in close coordination with the groundworker on site, was completed within a week.