A forest of booms - Lee Group's high reaches at work
By Lindsay Gale27 July 2011
Lee Group has begun work on an 8 acre site in the heart of the city of London, where it is demolishing two office buildings that cover 6 acres of the site, Eastgate House and the former Royal Band of Scotland building on Leman Street, in Aldwych on behalf of Berkeley Homes. The site is being redeveloped for residential occupancy and is attracting a lot of attention from the many passers-by in this busy part of the UK's capital city because of an unusual sight - the presence of four large high reach demolition excavators working together in a confined space to bring the structures down.
Lee was awarded the contract at the very end of 2010, with the demolition scheduled to commence at the end of March 2011. Both buildings had been fully soft stripped and decommissioned in 2009, meaning that Lee was able to commence demolition immediately it came on site. The seven storey Eastgate House is the first to be brought down and once its demolition is complete, Berkeley First, the construction arm of Berkeley Homes, will come on site begin construction on its footprint while Lee moves on to demolish the RBS building, while retaining the façade and other structural features, which will require careful planning and coordination. Three Hitachi high reaches (670, 650 and 470 models) began the demolition process, joined by the largest high reach in the Lee fleet - a Komatsu PC800LC with a reach of 43 m (141 ft) The machines commenced work from the former car park of the building - the only available open space on the site, which was a rectangular space no more than 42 m2 (450 ft2 in area. In fact, initially there was insufficient room for all four to work simultaneously, so the Hitachi 470 was used as a backup, with the three larger machines performing the initial demolition. Lee Group site manager Jason Williams told D&Ri that especially initially, they attracted a lot of attention, with up to 40 people at time watching them work and taking photographs of them in action. Certainly it is very rare for this number of large high reaches to be seen working together on one small site.
The initial completion date for the project was November 2011, but the phasing of the work changed following the award of the contract. Lee currently expects the project to take nine months to complete, but there is a possibility of some additional work that it may be contracted to carry out that might extend this period. Work can be carried out from 8.00 am through to 6.00 pm Monday to Friday, with Saturday working allowed from 8.00 am to 1.00 pm.
All occupants of nearby businesses and accommodation are being kept fully informed of the plans of the project - given it is part of a general strategy of urban renewal in the district, Lee reports that they fully accept that there will be a disturbance to their daily lives while the demolition is on-going and this is the cost of the improvements the redevelopment will bring.
Given the location of the site, efficient dust control is an essential. Lee was on site well before work commenced and identified that the space between Eastgate House and the RBS building was, in effect, a wind tunnel that would carry dust through to nearby occupied buildings. Therefore Lee erected a scaffold structure incorporating screening material at the rear of the site to minimise dust effects, In addition, a number of DustBoss units run continuously during demolition work, and all four high reaches make use of dust suppression systems at the end of their booms. One issue of the site is that there is only a single source of water on site, making water management a major issue.
Eastgate House consists of a five bay deep reinforced concrete structure and the inner three bays away from surrounding streets were brought down using the high reaches. The lower floors were then demolished by smaller machines. Currently Lee is bringing the outer two bays down using 3 tonne mini excavators and manual demolition working down the remains of the structure floor by floor. Once at ground level, the floor slabs are broken up using breakers and the basements cleared and then filed by processed demolition waste. A scaffold structure with monoflex sheeting has naturally been erected on the street side of the building to protect adjunct buildings and passers-by from falling debris. This type of protection will also be erected on the street side of the RBS building when work reaches that stage.
Debris is processed, with the steel rebar removed, by excavator-mounted concrete crushers. Once the demolition has progressed further to allow an area for a stockpile, this fill will be excavated and passed through a mobile crusher but currently there is no mobile crusher on site, It is expected that the demolition of the two buildings will generate around 80,000 tonnes of waste, the bulk of which will have to be removed from site. Currently some 20 loads a day leave the site but once demolition progresses further, there will be a greater volume of traffic movements on and off the site, in the order of 100 loads per day if Lee is to meet the schedule, but again the view is that this will be accepted without difficulty.
This makes the demolition work being carried out at the time of D&Ri's visit a critical phase of the project, since to achieve this level of traffic movements, Lee has to quickly clear an area sufficiently large to accommodate a number of vehicles on site simultaneously,
Although Eastgate House forms the first phase of the project, work has in fact also started on the RBS building, with 13 tonne excavators working on its roof. This was identified as being thicker and therefore heavier than originally thought and the high reaches with their 2.5 tonne tools could only process this heavier roof slab slowly. It was therefore decided to use a floor-by-floor approach on this phase of the RBS building demolition.
Currently 12 excavators and other equipment are operating on the site with a workforce totalling 45. This includes a team of five who are constantly engaged in dust suppression duties.