Positively The Biggest London Basement Ever

Generally speaking, open-cast mining on greenbelt land, construction of enormous sub-basements and supporting runway extensions are three things likely to be unpopular with both the planners and the neighbours. A new development in Hounslow, given planning approval in July, is therefore a bit of a surprise.

Abandoned farmland

The 110-acre site, formerly known as Rectory Farm, is adjacent to Park Road and the Parkway, with crowded London suburbs on one side and Heathrow on the other. Farming was abandoned there in 1996 and subsequently three applications to extract gravel from the site have been made – the first two declined because of noise, dust and traffic concerns.

The geology of the area consists of deep gravel terraces laid down in the Pleistocene era on top of the ubiquitous London clay. Approximately three million cubic metres of that gravel can be extracted over the course of twenty years, to be used in construction projects across Greater London, including another runway for Heathrow Airport, and huge basement constructions to be used as warehouses.

New park

Key to getting the support of residents and council planners is the proposal to landscape the surface above the gravel mines and warehouses into parkland. Converting the voided space into huge basements to support the park above is therefore integral to the design, but a top-down construction method is needed to make it possible. Otherwise it would be impractical to open the site as a park until 2040 when the gravel extraction is exhausted.

The project is a joint effort involving landowner Formal Investments, architects Carmody Groarke, consultants DP9 and Gleeds, landscape architects Vogt, and engineers from Arup. They will use top-down methods like those employed to build tower blocks in the City. Topsoil will be returned to cover a concrete slab supported on deep piles, and the gravel gradually extracted later. The cavern will be at least ten metres deep. Normally it’s an expensive method, but assisted in this case by the proximity of the aggregate to build it from. The gravel is expected to supply the bulk of London’s requirements for new constructions for the next fifteen years at least.

Neighbourhoods around the development have been assured the result will be an “undulating and botanically diverse landscape” and “accessible to the public from day one” (a slight exaggeration) and linking communities with new safe routes to school and work. It will also be the largest British park constructed in one hundred years. Neighbours have been promised it will include all-weather football, hockey and cricket pitches.

Public support

Of 350 members of the public who returned questionnaires, more than 97% are said to have wanted the park. Chairman of the Heston Residents Association, David Blackett, also came out in favour, as did Gordon Scorer of the London Wildlife Trust.

The new underground structures will easily be the largest basement construction in London, enclosing 180,000 square metres of space and dwarfing notorious millionaire developments in Kensington.

The first area of parkland is scheduled to open in 2020, with the first basement warehouse space available in 2022. There will be 2,500 jobs generated over the course of the site’s construction and subsequent operation.