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Incremental launching forming machine for the world´s longest underwater tunnel

HONGKONG/CHINA, May 29, 2013 - With the help of PERI know-how, the longest underwater tunnel in the world is currently under construction in China. Two hydraulically-operated shuttering machines are being used for the efficient realization of 33 tunnel elements by means of the incremental launching method. Each standard element is an incredible 180 m long and weighs over 70,000 t.

In southern China, a very ambitious transport project is currently being realized: a 35 km long road connection across the Pearl River bay which is aimed at allowing Hong Kong to grow both physically and economically with Macau as well as Zhuhai on mainland China. One part and, in a sense, the central element of this mammoth project is the 6 km underwater tunnel – the longest in the world. Then, in the western area of the approach flight path for Hong Kong International Airport, Chek Lap Kok, the six-lane carriageway is positioned 45 m below the surface of the stretch of the water which in turn is the most important shipping route between the Pearl River and South China Sea. Two artificial islands form the transitions between the tunnel and bridge structures.

The longest underwater tunnel is under construction

With the help of two hydraulically-operated Peri formwork machines, the world´s longest underwater tunnel is currently under construction in China. | photo: Peri GmbH

Impressive field factory

In an impressive field factory near the site, two production lines are being used to produce a total of 33 tunnel elements. The dimensions are enormous as each of the reinforced concrete tubes for the standard sections is 180 m long, 38 m wide, 11.40 m high and weighs 72,000 t. With the help of the two PERI forming machines, 22.50 m long sections are constructed one after the other each time using the incremental launching method. Altogether, eight such segments form one tunnel element. Completely extended hydraulically in a dry dock, these reinforced concrete "prefabricated parts" are sealed at both ends with waterproof bulkheads, then positioned at sea level by means of a lowering basin and prepared for being towed out. Pontoons stabilize the tunnel sections during towing operations to the final position in the open sea.

Project-customized Peri Engineering

Per production line for two tunnel tubes and a centrally-positioned service gallery, the hydraulically-operated Peri formwork solution consists of six main structural components: slab formwork, two external and three internal sets of formwork. In addition, two different sets of stopend formwork ensure correctly positioned accommodation of the sealing between the individual 22.50 m long segments as well as at both ends of each 180 m element. Together with the 50 m long truss girders in the centre, the internal formwork forms a horizontal moving device in order to return to the concreting position after each operation and thus retract into the prefabricated reinforcement cages. For ensuring efficient construction throughout, the shoring construction and portal crane are likewise important components of the Peri overall concept.

Construction of the underwater tunnel

The finished tunnel tubes with lengths of 180 m are moved from the field factory into a dry dock, sealed with bulkheads and lowered gradually to reach sea level. Pontoons stabilize the tunnel sections during towing operations to the lowering point in the South China Sea. | photo: Peri GmbH

Monolithic tunnel without anchors

The advantage of the Peri process engineering is that the bottom plate, external walls and slab can be constructed monolithically and, in particular, without anchors. As a result, thousands of tie points can be saved which minimizes the danger of leakage and improves work operations. Around 30 hours are required for concreting a complete segment with approx. 3,600 m³ of concrete being formed. With the help of the two Peri shuttering machines, close to one million cubic metres of concrete will be processed to create "prefabricated components" which are then joined together on the seabed to form a tunnel structure. The HZMB tunnel has been designed to ensure an exceptionally long service life of 120 years – placing enormous demands on all the construction materials used and requiring site personnel to achieve the highest level of quality standards, all within a tight construction schedule.

Ambitious transport project

When including all access structures, the Hong Kong-Zhuhai-Macao road link has a total length of 50 km. Apart from the 6 km long tunnel crossing, two suspension bridges serve to ensure the unimpeded passage of cargo and passenger ships. The bridge and tunnel constructions have been designed to withstand earthquakes of up to 8.0 on the Richter Scale as well as wind speeds of 200 km/h. Construction costs amount to around 7.6 billion euros. The new route will be open to traffic in 2016 and will shorten the journey time from Hong Kong to Zhuhai from four to just one hour.

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