This project involved the conversion of a Grade I listed building in the centre of London, housing a former Bank of England holding vault in the basement.
The deconstruction and removal of the heavily reinforced vault posed particular constraints on the work - 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 into 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 to preserve the structural integrity of the original building – this applied even to fixing holes.
Diamond Cutting & Drilling
The only method approved was diamond cutting since this gives the advantages of minimum vibration and noise and reduces dust and debris.
Gnat was given just six weeks to complete the job using a combination of track sawing and stitch drilling to remove 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!
Isolation and Removal
Blocks approximately 1-metre square were cut and removed using a 3-phase electric Brokk remote-controlled robot modified for lifting. These were transported away to another holding area, drilled and hydraulically burst into manageable-sized sections to assist removal from the tight confines of the basement area.
Hilti Track Saws and Drill Rigs were used for the sawing and drilling. These provided the high power needed for an arduous task such as this. Several 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.
Completion on Schedule
The job was completed successfully with two days to spare, including 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 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. 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!