Demolition, Temporary Piling and Services Diversions
9th Ocotber 2007
Kempson House demolition
Kempson House, on the eastern part of the site has now been demolished down to 3rd floor level. The lowest three floors are being enclosed in a sheeted scaffold. The building will then be demolished to street level, which will be achieved by the end of the month.
90% of the materials arising from demolition are being recycled, with timber and metals being separated on site, whilst rubble is transferred to a waste transfer station where it will be crushed and reused.
Bishops House demolition
The roof top plant rooms to this building, facing Bishopsgate, have been removed and demolition is progressing down towards the 8th floor. Much of the east and west facades are formed of pre-cast concrete panels which are being lifted off whole.
Now that demolition is in hand, the building will come down about one and a half floors per week.
Temporary piling
Temporary king post piles consisting of a steel tube grouted into a bored pile some 9 m long have been installed for most of the Camomile Street frontage, together with parts of Outwich Street and Bishopsgate frontages. These will form part of temporary king post and reinforced concrete skin walls to support the surrounding streets whilst the new basement is constructed. In other parts of the perimeter contiguous piles - reinforced concrete bored piles at close centres - are being installed for the same purpose.
The rigs used to install the king post and contiguous piles are moving from area to area as and when demolition operations above allow safe access.
In order to install the king post piles along much of the frontage in Bishopsgate , it will be necessary to occupy the footway with piling rigs. We have therefore arranged with TfL that from Monday 15.10.07 for 6 weeks the southbound slow lane in Bishopsgate will be closed to vehicles so that pedestrians may use this whilst piling rigs occupy the footway.
Skin wall construction
The construction of the temporary skin wall between the kingposts along Camomile Street has commenced. The operation involves excavating a trench about 1.2m deep between a pair of kingposts set at 2.5m centres and then promptly casting a reinforced concrete wall panel between the posts. The king posts are then propped. Excavation and construction of the adjacent wall panel then proceeds.
Once the upper 1.2m panels have been completed, the operation moves to a lower level and panels between 1.2 and 2.0m below street level are constructed and propped. Four levels of panel will be needed to support the height of the existing basement. This piecemeal pattern of construction ensures that the ground beneath the highway is supported at all times.
Archaeological investigations
Whilst the superstructures of Kempson and Bishops houses are being demolished, the Museum of London Archaeology Service is busy in the basements cutting two trenches between the foundations of the buildings. The profile of the Roman ditch that lay outside the City wall is appearing.
No significant finds have appeared to date, but the geometry and location of the ditch will enable one more piece to be slotted into the maps of the City's history.
Services diversions
Having commissioned the temporary transformer located on the closed section of footway in Outwich Street, EDF have de-commissioned their chamber in the basement of Kempson house and will shortly do similar to the chamber in Bishops house. This operation will involve another excavation at the Bishopsgate/Houndsditch junction.
National Grid (gas) and Thames Water still have further works to execute around the site which will involve a number of excavations, but we do not yet have timetables from them for this work.