CampbellReith has provided multi-disciplinary engineering advice to Big Yellow for almost 20 years. This Guildford site was in a disused state and had a significant industrial history. It had been subject to remediation in the past, resulting in poor foundation conditions. The development proposal involved a requirement for part of the site to be developed into a portal framed warehouse (used for self-storage) and the remainder being sold off to a potential food retail developer.

Located next to a Network Rail main line and Thames Water sewers, consideration was given to the client’s commercial interests as well as their technical requirements. To maximise the useable area of the site, a retaining wall was constructed along the western site boundary to allow removal of an embankment slope that supports a live railway line. At depth the site was also underlain by a sewer operated by Thames Water and a significant electricity cable. Given the sensitivity of the rail track to ground movements, a high-quality investigation and advance ground movement analysis were required. Bearing this in mind, along with the prevailing access constraints associated with the embankment slope.

CampbellReith appraised a number of unconventional investigation options with contractors on their ISO14001 Approved Supplier database. Options considered ranged from specialist slope climbing drilling rigs to excavator boom mounted cone penetration testing equipment. Close liaison with the interested third parties such as Network Rail, Thames Water Utilities Limited (TWL) and UK Power Networks were undertaken throughout the works, and approvals for the design solution obtained.

Good quality soil sampling, in accordance with Eurocodes, was also required to facilitate sophisticated geotechnical analysis and to ensure that Network Rail requirements were met. Whilst WALLAP was used to design the retaining wall, reference was also made to a contemporary article in a trade journal (Ground Engineering) to model wall and ground displacements. With respect to the TWUL sewer, a build over agreement was obtained and the piles designed to ensure that no load was shed on to it.

Subsequent to interpretive reporting, the geotechnical team helped prepare the piling specification in close collaboration with their structural engineering colleagues. The geotechnical team participated in value engineering exercises with the contractor and was also responsible for assessing the results of pile load tests. The building was completed successfully, and the store opened to the public in 2018.