Demolition and construction

Track possession times will be limited to a maximum of 5 hours per night (00.30 – 05.30 hrs). This is a key constraint to the works, limiting a large proportion of the heavy structural works to only be carried out during track possessions, at a time when ambient noise levels will be at their quietest.

The overall programme for demolition and deck construction will be 21 months, and will be divided into two primary stages at the eastern & western ends of the site.

Construction Activity	Date
Complete rail service diversions	Month 5
Commence demolition works	Month 4
Commence foundation for first section of deck	Month 6
Complete first section of deck over track	Month 9
First phase of raft complete	Month 14
Temporary station open for access to station	Month 18
Raft Structure complete	Month 24
New station complete	Month 33
Commercial offices complete (shell & core)	Month 38
Commercial offices complete (Cat A)	Month 41
Residential building complete	Month 36
Project Completion	Month 41

Demolition Methodology

The demolition works at South Kensington Station will fall into three sections as follows:

Demolition of adjoining buildings at 20-34 Thurloe Place
Demolition of structures within the station environment
Demolition of the existing station, shops and arcades

Night-time work

Approximately 250 full track possession periods at night (between the hours of 00.30 – 05.30) over an 18 month period will be required for foundations and raft construction. Track possessions will be required for all works to be undertaken alongside or over the railway, which is virtually all work prior to deck completion. Thereafter, almost all of the works to be undertaken under the raft, such as station finishes, will also require full track possessions. However, the latter night-time works will not be as significant in terms of noise, as once the deck is in place it will act as a noise barrier for the works to be carried out underneath.

Construction Methodology

The major long-span beams over the railway will be launched using bridge-construction techniques, which will avoid the need for repetitive oversailing of the railway. Piling rigs will operate from deck level above the station.

Erection of New Deck Structure

The works will comprise the erection and installation of steel deck beams across the existing railway cutting, installation of secondary beams, precast decking structure and insitu concrete topping.

It is proposed to launch the deck beams (using bridge-building techniques), once erection of the first beam, using a mobile crane, is complete. These preparatory deck construction works will take approximately 2-weeks of night-time work.

A total period of 52 weeks will be required to construct nine bays of deck. Each bay will take 4 weeks to be erected. Breaks will occur in the sequence of works for foundation and canopy removal work. The works sequence for each bay will be:

One 1-week period to install primary beams, (these will be launched by sliding at night, but will be prepared during the day).
A further 1-week period for secondary beams (to be craned at night for rail safety reasons with preparatory works to be carried out during day-time periods).

Preparatory Work to Install Pile Casings

Piling will be carried out during the day, although some preparatory work to install piles casings at platform level will be required during Engineering Hours. These works will involve night-time lowering of steel casings using mobile cranes, operating from deck level through pre-formed holes in the deck structure at each pile location. The casings to the underside of the concrete deck will then be mechanically fixed using bolted steel fixings.

It is envisaged that these works will require 5-6 nights over the duration of 2-week period, during which a mobile crane will operate for approximately 50% of the time.

Demolition of Existing Station and Retail Units

The above works will involve demolition of the existing structure to street level and demolition of the existing station concourse slab over the railway.

Demolition of the deck structure will be carried out in two stages, bay by bay. The first stage will involve the breaking out the concrete slabs to the structure.

The second stage will involve the cutting and removal of beams spanning over the trucks, attended by a tower crane, or visiting mobile crane, for a period of up to 4 weeks (15-20 nights) over the duration of a 12 week period.

These works will need to be carried out at night to comply with LUL operational requirements.

Construction Traffic Impact

Trip distribution estimates of construction traffic show that during demolition there will be an average of 6 vehicle trips per day for approximately 10 months in total carried out over the duration of the construction period (peaking between 11-13 trips during material transportation). An average of 11 vehicle trips per day over a 32-36 month period, (peaking at 24-26 trips) is expected during construction of the Shell and Core.

A large number of movements (4,000) are expected over the entire demolition and construction period.

Noise

With respect to the night –time works, it is anticipated that there will be a core period of about a year, during which the night-time noise levels at residential properties (circa 25) immediately facing onto the site will exceed the target levels, albeit in some case by a small margin, for about half the night-time possession periods (170-180 nights). Though with modifications in plant and use of acoustic sheds it should be possible to reduce this proportion to about 25% of the periods involved. Nevertheless, specific noise compensation measures will need to be considered for the affected buildings.

Source: Environmental Statement, submitted on behalf of London Underground, Stanhope and Hutchison Whampoa in 2003 application