Tunnel formwork in Algiers with record-breaking dimensions
With a length of 144 m and a width approaching 23 m, the "Place des Martyrs" metro station boasts some very impressive dimensions. In addition, the entire 1.7 km long extension of the Algiers metro system runs under historic ground. For this project, an international team of PERI engineers designed economically optimized tunnel formwork solutions, tailored to meet the varying requirements.
The northernmost, most central as well as closest-located point to the harbour area of the extensive metro expansion measures is the "Place des Martyrs" station. The arch-shaped stop is 144 m long and 23 m wide – and will be one of the largest subway stations in the world after completion. The construction project is part of the ambitious infrastructure development plan designed to expand the current almost 9 km long, single-line metro network in the Algerian capital to a total of 55 km in length and featuring three lines over the next 10 years. The modern metro system will help to reduce the daily traffic jams and increase the mobility of the city's residents. With a population of more than 3 million inhabitants, Algiers is also the most important transport hub in Algeria.
Two cross-sections – one formwork carriage
"Place des Martyrs" features two different cross-sections. The imposing arch width of 23 m in the middle section, tapers in the northern and southern directions resulting in 16.50 m widths respectively. PERI engineers developed a formwork carriage construction on the basis of the VARIOKIT engineering construction kit in order to be able to cost-effectively realize both cross-section variants whilst using the same system components and formwork segments. Furthermore, special attention was paid to the design of the bracing during the planning phase as the concreting cycle length of 5.10 m is relatively short.
Based on the VARIOKIT modular construction system, the PERI formwork carriage solution is ideally suited to meet all project requirements: user-friendly as it can be hydraulically operated with a control panel, cost-effective due to the rentable system components, and it can be quickly assembled or adapted by means of standardized bolted connections. Supplementing the VARIOKIT formwork carriage construction is a PERI UP working scaffold. This has been optimally adapted to match the cross-sectional geometry of the arch and ensures the rapid and safe execution of the waterproofing and reinforcement work in advance of the tunnel formwork carriage.
The VARIOKIT modular concept
VARIOKIT is designed to accommodate the known load combinations of the tunnel, bridge and high-rise building construction. With standardized, rentable system components and site-compliant connection means, supporting formwork can be cost-effectively realized and geometrically adapted to suit the structure. For the construction of traffic-related structures with low usage, in particular, the rapid availability of materials as well as the quick and easy assembly results in enormous time and cost savings. Moreover, PERI VARIOKIT project solutions together with the corresponding equipment options can be tailored to fulfil the respective project requirements.
Currently, the African metro project includes the construction of the twin-track tunnel along with the development of two metro stations. To the north of the "Tafourah" end station, located close to the palatial Grand Post Office, Line 1 is being extended by a total of 1.7 km with the addition of the "Ali Boumendjel" station (Emir Abdelkader Place) and the "Place des Martyrs" station. Construction work is being carried out within the city centre which features numerous mosques and palaces as well as under the historic old town (Kasbah) which is a UNESCO World Heritage Site. This has presented a major challenge for all project participants.
Comprehensive tunnel formwork solutions
The formwork and scaffolding solution for the entire construction project was developed by a team of PERI engineers from Algeria, Portugal, Spain and Germany. A total of four tunnel formwork carriages are being used: in addition to the VARIOKIT formwork carriage construction for the "Place des Martyrs", a second project formwork carriage with a 9.30 m radius is being utilized for the realisation of the "Ali Boumendjel" intermediate station. Two other project-specific tunnel formwork carriages are being used for the construction of the 1,450 m long tunnel with its 4.50 m radius. This means that almost 10 m reinforced concrete tubes are being formed and concreted using mining techniques on a daily basis.