Tower Crane & Scaffolding Erected, Demolition started
14th August 2007
Tower crane erected
A tower crane has been installed in the centre of the site. This will be used for lowering demolition materials from the highest level to the street, a method that produces much less noise and dust than conventional methods where material is handled floor by floor down the building.
This crane will remain in place until November when the demolition of the two buildings will be approaching street level.
Scaffold erection
Kempson House is now encapsulated within a sheeted scaffold allowing demolition of the upper parts of the building to commence. The sheeting helps to contain noise and dust from the demolition process.
Bishops House scaffolding follows shortly behind. The scaffold has been cantilevered out from the building at 2nd floor level to enable preparatory operations for the temporary works to support the highway, necessary when the new basements are created at a later stage in the project, to be carried out concurrently with the demolition of the upper parts of the buildings. With the cantilevers completed, the footway in Bishopsgate has been re-opened to pedestrians and the carriageway is operating at full width.
Demolition started
A substantial amount of the fixtures, fittings, internal walls and doors have been removed from within the two buildings. Metals, timber, and rubble elements are being stripped separately such that each can be recycled, and where this is not practicable then the mixed waste is being sent to a sorting centre, where all that can be is sorted for recycling.
The upper levels of Kempson House have been stripped of the building services plant that was mounted there, and demolition of the structure has commenced. This will be a progressive operation starting from the top, breaking up the concrete structure floor by floor.
Breaking operations will be carried out by machine. Inevitably this operation is relatively noisy. The hours during which breaking will be carried out will comply with the voluntary quiet periods suggested in the City of London's Code of Practice. These are 10:00 - 12:00 and 14:00 - 16:00 hours.
To lay the dust during the breaking and clearing operations we will be using fog water sprays. These create a fine mist of water particles damping surfaces and laying dust as it is created. Under some weather conditions this fine mist itself can appear to be smoke or a dust cloud blowing from the top of the building.
The arisings from the demolition are being craned down and will be loaded into road transport between the two buildings. Hard materials are being taken to an off-site crushing plant where the prepared for recycling.
Temporary piling commenced
Whilst then new basements and foundations are constructed in 2008, it will be necessary to support the surrounding highways. Two methods will be used in differing parts of the site:
The first requires the construction of closely spaced bored reinforced concrete piles which will then be propped with steel sections as the excavation of the basements progresses downwards.
The second requires the installation of vertical steel kingposts founded in reinforced concrete piles. As the excavation then progresses downwards, the king posts will be propped with steel sections and panels of reinforced concrete "skin" wall will be cast between the kingposts, each panel below the previous.
Both methods use a powered auger to bore for the construction of the piles. This has commenced work in the corner at the junction of Camomile and Outwich Streets.
Archaeology
The Planning Permission for the tower is conditional upon an investigation being executed into the archaeology beneath the site.
The Museum of London Archaeology Service have been employed by our Client Heron Properties to carry out this investigation. Much of the potential archaeology on the site has been removed with the construction of the existing buildings in the 1960s and 70s but two areas are believed to remain undisturbed between the foundations. The basement slabs in these areas are being cleared and the foundations propped so that the archaeologists can commence their investigations from the basements whilst demolition proceeds at upper levels.
Services diversions
EDF have installed new high voltage cables within a service tunnel located underneath Houdsditch and have energised a new temporary transformer located in the closed footway on the west side of Outwich Street. This will maintain local capacity whilst the substations contained within basements of the existing buildings are removed and later rebuilt as part of the project.
Completion of the cable installation will allow them to tidy up the areas at the junction of Outwich Street and Houndsditch, though they have further excavations to excavate for low voltage cables at the Houndsditch/bishopsgate junction and in Camomile street.
National Grid (gas) and Thames water have further works to execute around the site which will involve a number of excavations.