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Case Study - Silent Bank Job in Grade 1 Listed Building

The conversion of a property in the centre of London into a residential property involved the careful removal of a heavily reinforced concrete basement vault - the property had previously been a Bank of England holding vault!

The fact that it was a Grade I listed building imposed many restrictions on the method of removal and diamond sawing and drilling proved to be the only acceptable way of completing the job on time and to the full satisfaction of the client.

It is quite common nowadays for many of the older buildings in the major cities in the UK to be renovated and refurbished for private residential use. A recent example was the conversion of a Grade I listed building in the centre of London in which was housed a former Bank of England holding vault. This posed particular constraints on the work, especially when it came to the deconstruction and removal of the heavily reinforced concrete bank vault within the basement.

The walls and roof of the building were built during the 16th and 17th centuries and the concrete walls and ceilings of the vault were added much later and were tied in to the existing structure in the majority of areas. The structural engineer in charge of the project insisted that all work carried out on the building should be non-percussive in order to preserve the structural integrity of the original building – this applied even to fixing holes. The only method that was approved was diamond cutting since this gives the advantages of minimum vibration and noise and also reduces dust and debris. Gnat UK, a specialist diamond drilling and sawing company and DSA member were called in to carry out the work. Gnat has been in the diamond drilling and cutting trade for over 20 years and own one of the largest fleets of robotic machines in the UK including 3 of the latest Husqvarna machines.

Gnat were given 6 weeks to complete the job and they used a combination of track sawing and stitch drilling to remove the walls, floor and ceiling. The walls and ceilings were 350 mm thick and the floor was nearer 700 mm thick. All were heavily reinforced, especially the floor which had in fact been designed to resist diamond drilling!

Blocks approximately 1 metre square were cut out and removed using a 3-phase electrically powered Brokk 90 remote controlled robotic machine modified for lifting. They were transported away to another holding area, using the Brokk, where they were drilled and hydraulically burst into manageable sized sections to assist removal from the tight confines of the basement area.

Hilti machines were used for the sawing and drilling – LP 32 track saws and DD 500 drill rigs. These provided the high power needed for an arduous task such as this. A number of suppliers were used for the consumables but in general Hertfordshire Diamond provided the 900 mm diameter saw blades and Golz the 107 mm diameter drill bits.

The job was completed successfully with 2 days to spare and that included a hold up following the discovery of asbestos on site. Gnat’s operatives are trained in asbestos awareness and they alerted the main contractor when they came across some suspect thermoplastic tiling. Work was suspended for a week for this to be dealt with by a specialist company.

The main structure was carefully monitored throughout the work and no movement or damage was caused and the occupant of the office on the other side of the party wall, an ex - Prime Minister, was blissfully unaware of what was occurring only a few metres away.

Mike Hill, Gnat UK’s Project Director, has been invited to a meeting with the American client who was “absolutely delighted that the works had gone so well” to discuss the next phase of works due to begin later this year.

Contact us to see how we can help you! Gnat UK Ltd

Hilti Track Saw tackling heavily reinforced bank vault walls