National Highways’ Spooner Row Depot in Norfolk required development to enable construction of a 3,000 ton capacity salt barn. A new perimeter retaining wall with minimal footprint was needed to manage the embankment area adjacent to the busy A11.
The contract to carry out the construction of the new salt barn and associated works was awarded to STP Solutions. Surveys showed to manage the embankment, a perimeter retaining wall of 50 linear meter with returns at both ends and a maximum height of 3.660m indicated a retaining wall of approximately 170m2.
Space was limited and it was important to preserve as much of that as possible, this meant finding a solution that could provide a small footprint, be structurally sound and quick to build.
STP then engaged with Tailor Engineering, who concluded the structural design of the precast modular block (PMB) retaining wall.
Tailor Engineering worked closely with STP to finalise the design and interpreted the site investigation to allow for a shallow foundation pad consisting of 150mm compacted GSB. The base layer of blocks would also be embedded to 450mm.
AD Bly were employed by STP to assemble the structure, with a gang of two men utilising an excavator to carry out the work. Deliveries were staggered which meant a nearly ‘just in time’ assembly program maximising the area available for storage.
The assembly method of placing two rows of blocks and backfilling meant no requirement for temporary works. This process was carried out until the required height was achieved. Assembly moved on at pace allowing completion a week early.
Sheet piling had been considered, however the possibility of exceeding depths of 5m and encountering hard rock could have increased the cost considerably. This was not the case with the chosen PMB where the foundation pad design was in place and cost effective in terms of materials, assembly, labour and plant.
