G&S — Site Visit — Woolwich Arsenal Crossrail Station
On the 16th November 2016, ten graduates and student members of ICE visited the Woolwich Arsenal Crossrail station for a site visit.
Background
The Woolwich station is on the south-east portion of the Crossrail/Elizabeth line that ends at Abbey Wood. The proposal for construction of a station at Woolwich was recognised by the House of Commons Select Committee in March 2007, as it was not part of the original Crossrail route. The construction of the station box was completed in February 2013. Balfour Beatty was awarded a £70m contract by Crossrail Ltd to fit-out the Woolwich Station and Portals in September 2014.
Scope of Works
The scope of works comprises new build ticket hall, plant rooms and back of house areas for the new station at Woolwich Arsenal and fit out of surrounding portals. The station consists of a sub-surface box station, 256m long and between 22.4m and 26.6m wide, which comprises a public entrance and back of house areas in the West Box, emergency escape, plant, and back of house areas in the East Box and a 241m long island platform area connecting the two Boxes 20 metres below ground level. A number of Systemwide interfacing contracts are in place which has an influence on works by the C530 contract.
Site Induction
The site visit briefing session was a great opportunity for the graduates and student to learn about the site specific safety systems, project programme and meet the Balfour Beatty team on site. All the site visitors were inducted and provided with the appropriate PPE (hats, boots, hi-vis jackets , trousers, gloves and goggles) during the session.
The site consists of two boxes (East & West) which are connected through the platform. The West box is where the ticket-hall area will be while the East box is only back-of-house rooms for the MEP facilities and staff.
We got explained the current activities on site; mainly MEP installations, screeding works and steel angles installations.
MEP Installations
Regarding the MEP what was very interesting is that the MEP design governs the Architectural design, since the purpose of the rooms is to fit the the mechanical equipment and not people. For example, we went into the fans rooms (necessary for the pressurisation design) and we were told that the size of the room is designed just to accommodate the fans.
Screeding works
As for the screeding works, we went on the roof where we got explained the sustainable approach of the design, where the roof will be brown. Also, we talked about the drainage system , which is inseparable with the inclinations. To achieve the required inclinations as per the design, the contractor (Balfour Beatty) thought initially to do it by adjusting the screed height accordingly and the works proceeded on this basis. However, after the completion of about 5% of the roof screeding works, the engineers realised that the slab is not designed to accommodate such a heavy screed loading (as the height at the edge of the roof slab needed to be 700mm at the highest point). So, an alternative solution was adopted. The built screed has to be broken and an inclined installation to be placed on top of a 50mm screed, which has the benefit of a lightweight system.
Steel angles installation
Also, the installation of the steel angles was a very interesting package. The angles , called head-restraints, are required to hold in place the secondary concrete walls. These walls are secondary as there is a gap between them and the soffit above, which allows the slab to deflect. This gap is 50mm and as a result the walls are behaving as vertical cantilevers. The angles are connecting the walls with the soffit and their role is to hold the walls in place in case of a blast or a high wind pressure.
We also had the chance to go at the platform level and saw the rail tracks which belong to another Crossrail contract.
The Tunnel Boring Machines (TBMs) Mary and Sophia were used to tunnel 2.6km from Plumstead to North Woolwich, called the Thames tunnel section. TBMs Mary and Sophia are named after the wives of Isambard Kingdom Brunel and Marc Isambard Brunel.
Final thoughts
The site visit at the Woolwich Arsenal Crossrail Station was a very successful and useful one. The feedback from the graduates and students was positive and we look forward to more site visits by the G&S Committee in 2017.
