The London Underground, the oldest in the world and the largest in Europe, comprises 11 different lines and 270 stations. Of these the Victoria Line is a deep-level underground route that was built in the 1960s providing interchange between The Tube tunnels and the Victoria mainline station terminus. The Victoria Line is the busiest London Underground line with more than 100 million passengers per year. The £741 million Victoria Station Upgrade (VSU) project was commissioned in order to relieve congestion at this busy interchange, upgrade the busiest station on London Underground and one of the UK’s strategic transport infrastructure assets. The upgrade required new entrances, a complex network of high level interchange tunnels, escalators and elevators, new ticketing offices and corridors, all to facilitate the high flow of passengers.
The complex network of passenger tunnels required various changes in section profile, so the secondary lining consisted of numerous geometries and profiles across the extent of the project. After a series of lengthy negotiations involving some of the best known European competitors in the field of steel moulds for in-situ casting, the main contractor (BAM Nuttall and Taylor Woodrow Joint Venture) entrusted CIFA with the entire steel formwork supply contract. The company from Senago secured the contract by proposing an innovative and highly-flexible technical solution that could be transformed on site to accommodate the changing profiles. The solution was based on flanged formwork built using various radii with minimum deflection tolerances coupled with a single carriage with a dual longitudinal length configuration and a variable height with different configurations. As explained by Giovanni Esposito, the Underground Area Manager for Europe, CIFA provided a formwork of 3 elements, with a total length of 5 m, that could be adapted to the 7 sections of the network and were transported by a long (≈6.85 m) motorised carriage travelling on rails.
The added difficulty in moving the equipment among the narrow connection curves of the tunnels was overcome by creating a particular system that allowed for the carriage to be shortened "semi-automatically" (≈3.50 m) by removing the longitudinal extensions, thus configuring it for the transport of just one element of forms. The problem of the different heights was overcome using telescoping legs with removable-flange trunks and supplementary external lifting cylinders.
These solutions allowed for the pre-assembled carriage to be lowered in the shaft in a reduced configuration, as well as for each 1.67 m ring of the formwork (weighing about 4.60 tonnes each) to be transported to the first and narrowest opening (PAL22). After having completed the transport phase, the carriage was extended semi-automatically in the vicinity of the first tunnel and was loaded with the 3 rings (tot. weight approx. 14 tonnes). The casting phase then commenced for the various sections, with adaptations being made to the regularity of the profiles, which were in-line with the tolerances specified by the designer.
An equally effective system was established for the casting of PAL10 escalator incline on a slope of 30°: A system of pulling cables fixed to a 7.5 tonne winch and an anti-tipping counterweight allowed the carriage to operate safely for both the transportation and positioning of the casting moulds. One particularly challenging aspect of the work was the transition sections – i.e. those between the horizontal upper and lower chambers and the 30° inclined escalator barrel. The complex three-dimensional change in geometry resulted in these transitions having multiple radii in both the horizontal slope and inclined planes, which resulted in a multifaceted trapezoid shape with a variable cross-section. The adaptable shuttering system developed by CIFA allowed TWBN to construct the transition sections using the same traveller and bespoke shutters simply fitted to it on site.
Along with the clever formwork design, the developed solution included a procedure for handling the geometric and structural details of each piece of formwork as well as transporting and positioning the formwork to complete the casting. The solution was implemented on site using a forklift secured using cables connected to a winch located in the upper chamber, which allowed safe passage of the formwork through the upper transition and down the escalator incline. The formwork, designed by Giovanni Esposito of CIFA, was symmetrically adaptable allowing it to mirror itself and so be re-used for the upper and lower transitions. Guided by the experience of Product Manager Luigi Scudellaro, the CIFA Tunneling technicians were on site to oversee the success of this solution. These works have served to highlight the uniqueness of CIFA's products, which is further evident in the statement by Miles Ashley, Programme Director of LU Crossrail & Stations, who said: "This was truly the first time that this system has ever been used to cast an inclined chamber, and it turned out to be a brilliant example of engineering being used to solve the problem of completing a casting on a steep slope.”
Vast majority of the works have been completed to the satisfaction of the client, through constant support provided by CIFA’s consulting service. The final stages of the works are currently underway and proceeding on schedule. The Taylor Woodrow BAM Nuttall JV team includes amongst others Menelaos Lydakis (Tunnels Sub Agent) and Tony Carrol (Tunnels Foreman). To view original press release click here or visit www.cifa.com 41/15
