Quay walls usually incorporate sheet and tubular piles, but contractors have completed an innovative concrete-based design at the container terminal of East Port Said.
Max Soudain reports from Egypt.
In just over a year's time, the new East Port Said container terminal is expected to open, marking completion of the first phase of an ambitious scheme to develop a new sea transport 'mega hub' in the eastern Mediterranean.
Approaching the site by boat on the newly-dredged shortcut from the east branch of the Suez Canal, the only indication of things to come is the brilliant white concrete deck of the new 1,200m-long quay wall gleaming in the desert. But soon huge dock cranes will be running up and down the quayside, loading and offloading cargo from massive container ships.
Planning began in 1997 and in 1999 the Egyptian Ministry of Transport awarded the build, operate, transfer contract for the container terminal to Suez Canal Container Terminal (SCCT), an international joint venture of Europe Combined Terminal Company, from the Netherlands, and Danish shipping firm Maersk Sealand, together with Egyptian investors.
SCCT awarded the construction contract to the Racon consortium (Italian contractor Rodio and Egyptian firm Arabian International Construction). The Maritime Research & Consultation Centre in the Ministry of Transportation awarded the design and engineering supervision of construction of the quay wall to Cairo consultant Hamza Associates.
The main design challenges were the extremely weak underlying soils, predominantly soft clays, and variable hydrological conditions caused by on-going dredging of the canal to allow the big ships to dock. The site had previously been considered 'unconstructable' by several consultants, says Hamza Associates chairman and founder Dr Mamdouh Hamza.
The first step was to characterise the ground through a multi-stage site investigation.
Unusually, all the bidding contractors joined forces before tendering began to obtain the best site investigation - 'the first time this has happened in Egypt, ' says Hamza. 'This meant the soil risk was transferred to the winning contractor, so we managed to eliminate Clause 12 [claims for unforeseen ground conditions].'
UK consultant Geotechnical Consulting Group supervised site investigations. Cone penetration testing was carried out, along with insitu vane tests, standard penetration tests and high quality sampling from boreholes using hydraulic piston sampling and rotary coring. High quality laboratory tests on these high quality samples provided calibration for the insitu tests and the input parameters for 3D finite element analyses (carried out using the Flac3D package).
Ground conditions comprise 5m of hydraulic fill and dredged silty sands and clays overlying, 8.5m of beach deposits (sand with broken shells) and the Nile Delta Clay - 15m of plastic clay with occasional sand layers followed by 30m of very plastic clay. Basal beds of alternating thick layers of sand, sometimes cemented, and stiff laminated clay lie about 60m down.
Despite initial concerns over the bearing capacity of the thick Nile Delta Clay deposits, soil properties were better than first thought, with clay strength 60% higher than previous estimates.
'The site investigation proved very successful, ' Hamza says.
Conventional design of quay walls usually incorporate sheet piles and tubular piles, he adds, but the higher strength of the clay meant that a different approach could be taken.
The design had to take into account not only the operating loads from berthing and loading and unloading enormous super tankers but also, in the short term, the effects of forming the 16.5m deep berthing channel in front of the quay.
The resulting quay wall is a concrete structure with a free height of 20m on the canal side and a 35m-wide deck. The main support is provided by transverse rows of four, 3m wide, 1m thick and up to 63m deep barrettes founded on the basal beds. The rows are 7m apart and barrettes are spaced at between 10m and 11m in each row.
A continuous 1m thick, 35mdeep diaphragm wall provides support along the front face and a similar 10m-deep structure runs along the back. The diaphragm walls comprise 3m long primary panels and 4m long T-shaped secondary panels, the 'T's connecting with the outer barrettes of each row.
Using concrete rather than steel allowed local materials to be used, saving about £16M, says Hamza.
Construction of the wall began in January 2000, 200m back from the water's edge. The first stage was to install sand drains across the area to reduce pore water pressure and to set up the dewatering system to keep excavations dry during construction. Next, a working platform was built by excavating up to 2m, replacing it with sand fill and crushed stone topping.
Guide walls, up to 1m deep, were then built for the walls and barrettes, with both being formed using hydraulic grabs under bentonite slurry. The Tshaped wall panels are fitted with steel stop ends to link with the primary panels. All the barrettes and the walls were then trimmed down to 0.5m below ground level and the longitudinal and capping beams cast.
A key element of the design is the removal of 5m of soil from inside the quay wall, reducing earth pressure on the structure and balancing the operating loads of the cranes. This reduces the effects of heave and lessens deformation of the structure.
The deck is designed to allow for the effects of the ground conditions, temperature variation and earthquakes. It is formed by precast elements laid on 3m high and 0.8m wide beams connecting each row of barrettes and connected to the wall capping beams by a cast insitu slab.
All dredging and coastal work is now complete. Construction of the container terminal will begin soon, with cranes arriving next year and the first ships due to dock in the first quarter 2004.