Morris Property Limited approached Menard for a Vibro Stone Column (VSC) quotation, and the works were subsequently awarded as a result of competitive tendering. The scheme is located on the edge of a small town and is part of phased construction of industrial development for Telford & Wrekin Council. The VSCs were required to support 3 no. starter industrial units, covering a total building footprint area of c.3,000 m2. VSCs have been installed beneath pad foundations (SLS bearing pressure of 150 kPa) and floor slabs to support a UDL of 45 kPa.
The site investigation indicated the presence of variable strength glacial deposits, consisting of a shallow crust of firm to stiff clay underlain by variably soft to stiff clays, typically over loose becoming dense sands. Kidderminster Formation Sandstone is present at depth below the superficial soils. The site has undergone some nominal regrading (+/- 0.5 m) to achieve the VSC platform levels, which were set at 200 mm below the proposed finished floor levels.
Prior to the VSC installation, near surface cohesive soil was removed (by others) where in close proximity to proposed trees, and these areas were backfilled with imported granular materials.
The VSCs were installed to depths of 3.0 to 4.0 m below platform levels, into the medium dense sands. A pre-augering rig was on standby to mobilise to site in case the VSC rig struggled to penetrate the stiff crust; however, it was not required over the duration of the works. The VSC installation, including a series of quality control plate load tests, took under 5 days to complete during a period of cold winter weather. Settlements have been limited to 25 mm total settlement with relative differential settlement of less than 1/500.