Geotechnical and Geoenvironmental Engineering

Shepperton Studios Limited appointed CGL to undertake a ground investigation on land to the northwest of Shepperton Studios as part of the first phase of ground investigations across the wider Shepperton Studios Expansion scheme and provide extensive geotechnical and geoenvironmental consultancy support for the redevelopment of the wider scheme totalling over 1 million sq. ft. of new production accommodation including 17 new sound stages.

The project required close collaboration between the client, designer and construction teams along with early contractor engagement to gain the confidence of the Regulator with respect to ground contamination and demanding structural tolerances to support this significant development.

A historical gravel pit, infilled with inert waste pre-Landfill Directive, was to be developed into three substantial sound stages in excess of 80m by 40m, workshops, car parking, a backlotand other production amenities. The Local Authority and Environment Agency (EA) required extensive consultation to permit the initial investigation of the sensitive landfill, and the proposed enabling and construction works.

Working with the client and structural engineers, a site investigation strategy was proposed during the height of the initial COVID19 lockdown. The investigation encompassed conventional cable percussive holes, CPT, window sampling, trial pitting and installation of extensive monitoring to identify the depth and nature of the infilling and the underlying natural geology and groundwater and ground gas regime. The project presented unusual earthwork challenges with the development of a platform to create a depth of benign material for a backlot that could support production needs for exterior set builds. All these emplacements are adjacent to the River Ash flood plain with associated soft-ground complications.

Ground raising, in combination with a critical need to protect sound stage floor slabs against future differential movements, led the design team to engage the main contractor, groundworker and specialist foundation contractors again at an early stage within the project timeline. The predominantly clayey landfill, underlain by dense granular deposits, dictated that the initial plans for both the frame and floor slab to be supported by a combination of CFA piles and VCCs.

Geoenvironmental challenges, addressing EA concerns required an assessment of the squeezing of the landfill volume by the VCCs, with the potential displacement of any leachate from the former landfill towards the River Ash, any discharges of landfill gas, and the penetration of the piling through the landfill creating a pathway into the natural soils. CGL’s modelling and direct communication with the Regulator enabled the remediation method statement to be approved in time to meet the tight timeframe.

Some 100,000msq of soil was redistributed to create the development platform and reduce the amount of offsite disposal. The CFA piling was redesigned to support the floor slabs replacing the VCCs. This design modification reduced the risk to the programme from rig unavailability and possible obstructions. Throughout the construction activities, regular reassurance monitoring of groundwater and surface water quality was undertaken by CGL to confirm no adverse effects to controlled waters as a result of the development works.

To date, the tight programme schedule has been achieved through pragmatic engineering decisions and communication with all parties. CGL is continuing to provide verification services including gas protection measure inspections, capping inspections and production of the final verification report to support the discharge of the final contaminated land planning condition.