Case Studies

Demolition, asbestos removal works and installation of piling mat – Cromwell House, 1–3 Fitzalan Place, Cardiff CF24 0ED

Fast-expanding hotel chain easyHotel obtained planning consent to demolish the vacant Cromwell House at 1-3 Fitzalan Place in the centre of Cardiff to make way for a new eight storey and 120-bedroom hotel, its first ‘super budget’ venue in Wales. Cromwell House is a 5-storey detached office building with basement car parking. To the front is Fitzalan Place which is the main arterial route into Cardiff from the east. The Cromwell House site is in Cardiff city’s leisure areas near Cardiff Street Station, Cardiff Bay, bars, restaurants, movie theaters and attractions, including the Doctor Who Experience at the BBC Roath studios.

Dorton Group secured the contract through competitive tendering. The scope of works included:

• Provision of a fully intrusive asbestos refurbishment and demolition survey and report.
• Schedule of condition of existing public pavements, roads and party walls and infrastructure.
• The disconnection of all utilies and services including the payment of all statutory authority fees and licenses.
• The removal of all asbestos contaminated materials.
• Removal of all previous tenants’ furniture, fixtures and fittings.
• Soft strip and demolition of the 5-storey detached office building with basement car parking. Demolition included the basement car park, all ground bearing slabs, lift pits and stairwell pits, including associated foundations.
• Demolition arisings were to be segregated, with suitable concrete arisings crushed to 6F2, and re-used on site for the installation of a piling mat.
• Design, supply and installation of temporary support works for the stabilisation of retaining walls along the front and rear elevations to the major highway Fitzalan Place and at the rear to Newport Road Lane.
• Design, supply and installation of perimeter ply hoarding, ‘freestanding’, fixed to posts supported by ballast boxes, for ease of re-alignment during future piling operations.
• Attendance of a Structural Engineer to plot pile cap positions.
• Installation of a piling mat and stable base for the piling rig along the perimeter of the proposed new buildings. The piling mat was to be placed on geofabric on well compacted sub-grade material laid in maximum 150mm thick layers with particular attention paid to ‘weak zones’. The ground had to be excavated in maximum 1.80m sections with the piling mat laid in the same sequence as the work proceeded to offer temporary support to the retaining walls in accordance with the Engineers drawings and specification.
• Six number plate bearing tests to British Standards were carried out at locations spread over the entire site area. The results were adequate for future construction operations – maximum applied sresses were very high in the region of 620kPa+ and in average yielded minimal settlement in the region of only 12mm.

The demolition and piling mat works faced complexities due to six main factors:

1. Delayed disconnection/ termination of the underground power supply cable due to an embargo on pavement works over the approaching Christmas and New Year holiday period. Protection measures had to be implemented utilising crash decks over the service route with adequate barriers and with all works in close vicinity stopped. A crash deck also had to be designed and installed over the adjacent electric sub-station under the supervision of the relevant statutory authority.
2. Due to constraints regarding operating space, the building had to be reduced ‘top down floor by floor’ and the site area cordoned off with full height scaffolding, close boarded at ground level with steel hoarding panels to the entire site perimeter and clad with monaflex sheeting. A complete exclusion zone was put in place around the entire site area which was only relaxed for the following demands. a) access and egress for emergency puposes. b) lorry movements in and out of the site. c) monitoring of site safety regimes necessary to check that the safe system of work was effective.
3. On each floor level a series of staggered drop holes had to be formed to allow the removal of rubble from floors above and directed into the basement. A protective barrier was erected around each drop hole to prevent any trip hazards. A structural Engineer was employed to determine floor loadings for the safe placement of mini rigs on each floor level. Temporary support was installed on each floor level in accordance with the Engineers recommendations under the direction of a specialist temporary works supervisor. The rubble on each floor level was cleared systematically and regularly to prevent the overloading of any area at any stage.
4. The city centre location meant that Dorton Demolition & Excavation Limited had to employ very strict measures in reducing and suppressing noise, dust and vibration. Noise, dust and vibration monitoring equipment was installed at appropriate locations and readings were monitored and managed at all times to ensure safe levels were not exceeded.
5. Very deep excavations with the lift pit ground bearing slab approximately 3.00m below existing ground level and its concrete base a further 2.00m deep.
6. The extreme weather that battered Britain. The UK was covered in weather warnings as Storm Deirdre battered the country in mid-December. Seven amber warnings were issued by the Met Office, covering almost the entire UK apart from London and the South East. Travel was disrupted after freezing rain was reported and roads were closed because of fallen trees.

The complexities were, however, adequately and efficiently managed. The project team undertook comprehensive planning, careful risk management and implemented and maintained open communication at all times. The project was delivered safely, with no incidents or injuries recorded, within programme and on budget.

Since handover of the site, piles have been successfully sunk with no obstructions encountered.