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Railing against the odds

Foundations Minipiles

London's Park Square is getting back its Regency railings. Nearly 200 years after they were first installed, it seems that minipiles are now a more economic foundation than the original strip footings.

Park Square, which sits between Regent's Park and Marylebone Road, is one of London's most exclusive addresses. It is rumoured that a property in the square changed hands recently for £60M - not bad for a terraced house, albeit a John Nash-designed exemplar of Regency architecture.

With ownership of one of these coveted properties comes access to the square's private gardens. Until the Second World War, this oasis of calm was separated from the chaos of central London by decorative cast iron railings. Like railings from other sites all over the capital, they were removed, ostensibly to be melted down as part of the war effort.

Yet remarkably, Park Square's original iron railings have recently been 'rediscovered', having survived the war and ensuing years entirely intact.

And now, some 60 years after their removal, the railings are being put back in their rightful place on a new but exact replica of the original Portland stone plinth. Given that most of the railings removed in the war were of no scrap value whatsoever (see box), there is much for which to thank whatever hidden forces were at play in preserving those from Park Square.

While the project is all about architectural and historical preservation, below ground the construction is decidedly contemporary. Whereas the original railings were supported by a shallow brick footing, they are being reinstated on a mini-pile supported reinforced concrete ground beam, complete with 100mm Claymaster heave protection board on its underside.

Vic Handley, business development director with piling subcontractor Van Elle, says this is simply because in the early nineteenth century minipiles did not exist. In the twenty first century, however, they are a more economic choice than strip footings - or rather the deep strip footings that would be required under current building regulations. With mature trees nearby and a layer of shrinkable clay below the topsoil, minipiles provide the most economic way of transferring loads into dense gravels 4m below the square.

Van Elle is using a Grundomat down-the-hole pneumatic hammer to drive the steel-cased piles. This vertical application of the popular cable moling tool has been one of the minipiling industry's secret weapons of the last two decades.

In forming the pile, the ends of a 100mm diameter permanent steel casing are crimped closed, and a dry plug placed in the bottom. After this, the mole simply drives the casing into the ground. It is then filled with concrete and a reinforcing cage placed within it. It is very fast and reliable.

The biggest problem is services, particularly along Marylebone Road. It is here that the original, grand gates are being reinstalled, replacing utilitarian ones put up in the 1960s.

Main contractor Killby & Gayford has taken responsibility for locating services. For piles in close proximity to services, it hand digs inspection trial trenches and pre-installs oversized steel casing down to below the level of services.

Van Elle then forms the piles inside the steel guide tubes.

Along with 311 driven piles, Van Elle is also constructing the reinforced concrete ground beam - 500 linear metres in total.

Tolerances are surprisingly tight, just 3mm.

The Portland Stone plinth is supplied by CWO. Blocks have joggle joints - v-shaped cuts in abuting faces which help with alignment and are afterwards grouted to key adjacent blocks. The plinth is secured to the ground beam using stainless steel dowels set in diamond core-drilled holes at intervals along its length. WT Specialist Contracts is also core drilling along the top surface of the plinth into which every single vertical rail is set in a resin.

Van Elle started on site in August. It is now nearing completion of its £100,000 contract and the project is scheduled for completion next spring.

According to Crown Estates, which owns the freehold on Park Square, the reinstatement of the railings is the culmination of more than 50 years of refurbishment following the war - after which two-thirds of the properties were uninhabitable.

Home of the Diorama

The east side of Park Square is one of the finest examples of Regency architecture.

Central within John Nash's faþade is the 'Diorama', the British example of a French invention of the early 1820s to create 'naturalistic illusions for the public' - in effect a painter's three-dimensional cinema.

Housed within a large rotating amphitheatre, huge pictures, 22m by 14m in size, were painted on translucent material with a painting on each side. By light manipulation on and through these flat surfaces, the spectators could be convinced they were seeing a life-size three-dimensional scene changing with time. The effect, as inventors LJM Daguerre and C Bouton proclaimed, could 'imitate aspects of nature as presented to our sight with all the changes brought by time, wind, light, atmosphere.'

To display such dioramas, with the various contrivances required to control the direction and colour of the light from many high windows and sky-lights, required a large specialist building.

The original Diorama opened in Paris in July 1822 and plans for a Diorama in London were set in motion at the beginning of 1823. Taking only four months to finish, the building was set in the centre of John Nash's facade along the east side of Park Square at the south-east corner of Regent's Park, it was opened in September 1823. Today the building is home to the Prince's Trust.

Cast iron excuse

During the Second World War, many thousands of tons of decorative ironwork and railings were removed from London's streets, supposedly for recycling into munitions and tanks as part of the war effort.

It now seems certain that the collection of aluminium pots, pans, railings and other metals was largely a propaganda exercise intended to give blitzed civilians a feeling of having contributed to the war effort and the opportunity to 'hit back' at Germany.

Metals such as aluminium and copper were indeed scarce and were probably re-cycled. But cast iron was of little value and it is now widely accepted that it was frequently - and secretly - dumped.

Decades after the war, Canning Town Dockers recalled towing barges down the Thames estuary to dump vast quantities of scrap metal and decorative ironwork.

They claimed that so much was dumped at certain spots in the estuary that ships passing the area needed pilots to guide them because their compasses were so strongly affected by the quantity of iron on the seabed.

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