Planning for this vegetated retaining wall ran into problems when it became apparent due to the existing road and services it was impossible to fit the width of geogrid reinforced backfill within the footprint available. Despite this, a 3.50m wide bench was going to be provided at mid-height of the excavation as a platform for the plant required to extract the cofferdam sheet piles.
To make the best use of this oddly shaped excavation geogrid reinforced fill was placed and compacted within the space available, to which Stabilisure geopins were connected to extend the reinforcement beyond the back of the excavation. The geopins were also taken advantage to improve the bearing capacity of the subsoil, both at the base of the wall and at the location of the temporary platform for extraction of the sheet piles.
By being able reinforce not only the engineered fill, but the soil behind it, the permanent works were able to blend with the temporary works in a way that achieved the low cost, low carbon footprint and minimal impact to existing structures and services under challenging conditions.