CAREFUL planning was a key ingredient in Controlled Demolition's approach to the demolition of Birmingham's Bull Ring.
The site, not great in size at 100 m by 80 m, presented a mixture of abutting structures built at various times since the turn of the twentieth century.
While the variety of buildings on the site presented problems, it also gave the company an opportunity to demonstrate several different methods of current demolition practice.
The job has put Controlled Demolition firmly in the spotlight. Its £1 million contract with The Birmingham Alliance - a partnership between property developers Hammerson, Henderson Investors and Land Securities - is part of the £400 million Bull Ring project, which the Alliance claims is Europe's largest current inner-city regeneration project.
'This is a high-profile job,' says Controlled Demolition's commercial director Darren Palin. 'Our work so far is just the start of a massive redevelopment programme in Birmingham's city centre. We are now tendering for the second phase of demolition work which will involve clearing the main Bull Ring market area.'
The site currently being cleared by Controlled Demolition for phase one of the project is on the periphery of the Bull Ring area. Although it has not escaped examples of the same 1960s concrete architecture that now blights the appearance of the Bull Ring shopping centre, it also contains structures built much earlier.
Controlled Demolition has so far removed an 11-storey '60s-built reinforced concrete office building, a four-storey reinforced concrete car park, the Ship Ashore pub and two masonry and steel railway bridges. A masonry goods yard office building has also been demolished, although its Grade II listed facade has been removed for reconstruction elsewhere (see box).
The last structure currently being demolished is a heavy reinforced concrete railway goods warehouse, designed and built to take the weight of freight trains which discharged their loads into the warehouse below via a series of trap-doors.
'The arrangement of the structures on the site has lent itself to demolition in reverse order of construction,' says Mr Palin.
'We have been able to start at the top and work our way down and across the site without any major difficulties. But some phases have required special consideration due to various constraints. For instance, the cantilevered edge section of the car park had already been deemed unsafe and propped to prevent it from collapse before we arrived on site,' he says.
'Small breaking machinery was used to take the structure back one bay at a time until it was a safe distance from a nearby road. Long- and medium- reach machines could then be used to complete the job,' says Mr Palin.
The St Martin's House office block adjacent to the car park was the first structure to be tackled by Controlled Demolition. The building was fully scaffolded and surrounded by debris-netting to contain dust and falling material before asbestos removal and soft-stripping of all fixtures and services was carried out.
'Mini-excavators fitted with breaking tools were used to demolish the structure floor by floor, from the roof down to the sixth storey. A CAT 245 long-reach machine fitted with a 27 m boom was then used to pull down the rest,' says Mr Palin.
'It took one week for each of the top five floors to be removed, whereas the remaining work was completed in just one week. Such is the effectiveness of using long-reach machines.'
The Ship Ashore pub, which had previously been fire-damaged and consisted of an RC and masonry two-storey structure supported on single storey columns, was then demolished.
'This work was carried out over a weekend period due to the height of the structure and its close proximity to the Park Street site boundary. Soft-stripping of the interior and asbestos removal was completed before the weekend work, which was carried out with traffic management in operation,' says Mr Palin.
Two railway bridges that carried railway goods yard sidings over Park Street were demolished during two 48-hour road possessions in March.
A soft strip was carried out to remove all non-structural material before the steel beams and masonry abutments were demolished to leave just the warehouse structure standing on the site.
The eastern boundary of Controlled Demolition's work is formed by Birmingham's old Moor Street station, which is Grade-II listed and has been superseded by a new station located further to the east.
A masonry retaining wall supporting the ground on which the old station stands - at the same level as the goods yard - also forms one of the walls of the warehouse below.
Controlled Demolition first has to prop the masonry before demolition of the warehouse can begin, says Mr Palin.
'There is a degree of uncertainty over the contribution the warehouse is providing towards the stability of the retaining wall so the props will be installed as a precautionary measure,' he says.
'We will also underpin part of the old station using mass concrete to mitigate against the risk of undermining its foundations above the warehouse.'
Demolition of the warehouse has also been given special consideration due to the unusual nature of its construction.The building was constructed around 1914 using a Hennebique method, devised in France for erecting structures from a series of standardised precast concrete parts.
'The warehouse is a heavy structure designed to take the weight of trains overhead and consists of reinforced concrete slabs on top of beams spanning at close centres from cross-beams and square columns,' says Mr Palin.
'The slabs are being saw-cut to separate the beams and weaken the structure before traditional techniques can be used to demolish the roof and then the columns down to the cobble stones.'
Mr Palin says Controlled Demolition has been carrying out a full recycling operation since it started demolition work at the Bull Ring.
'This contract is a good example of the extent to which we can protect the environment by recycling demolition materials. About 90 per cent of the material produced has been recycled and only plastics and asbestos have been taken to landfill,' he says.
'All concrete arisings have been crushed and recycled on-site and delivered to road contractors working around the Birmingham area. Some of the crushed concrete may stay on site for use by Balfour Beatty, which is due to start constructing new roads through the site after we have left,' says Mr Palin.
All steel and scrap metal is being salvaged from the site, as is a substantial quantity of bricks and cobble stones. All timber taken from the structures is being sent away for use in manufacture of chipboard.
Since 20 March, Controlled Demolition has been co-operating on site with the University of Birmingham Field Archaeology Unit, says Mr Palin.
'This is an aspect of demolition we are familiar with. Some parts of this site, which is close to Birmingham's original markets and St Martin's Church, are being cleared to ground level for the first time in nearly a 100 years,' he says.
'A team of archaeologists from the University will be working on eight trenches in search of mediaevel deposits and we will work with them and help them out for as long we share the site.'