A diaphragm wall solution for a quay at a new container terminal in East Port Said has tamed 'unconstructable' ground.
Max Soudain reports from Egypt.
Abrilliant white concrete deck stretching more than a kilometre gleams out from the desert as the Suez Canal prepares to meet the Mediterranean.
Soon it will be covered with huge dock cranes busily loading and offloading cargo from massive container ships.
When it opens in just over a year, the new East Port Said container terminal will mark completion of the first phase of an ambitious scheme to develop a sea transport 'mega hub' in the eastern Mediterranean. A vast expanse of untouched land, mainly desert, offers room for expansion and associated industrial development.
The US$310M scheme will be built in phases, largely dependent upon the success of the container terminal. The port is 1.3km east of the east branch of the Suez Canal (or Port Said Bypass) and 1km from the coast on a newly formed channel from the Mediterranean.
Future plans include extension of the quay wall from 1.2km to 7km and construction of northern and southern basins with liquid and dry bulk terminals and a further 5km of quay walls.
New road and rail links from Port Said, funded by the Egyptian government, are part of the first phase of the project. These include a road bridge at Kantara and rail bridge at El Ferdan crossing the Suez Canal.
Electricity, water and wastewater systems are also being built up.
Planning began in 1997 and in 1999 the Egyptian ministry of transport awarded the build, operate and transfer contract to Suez Canal Container Terminal (SCCT). This is a joint venture of Europe Combined Terminal Company of 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 and consultation centre in the Ministry of Transport awarded the design and engineering supervision of the quay wall to Cairo consultant Hamza Associates.
The firm devised the project masterplan and designed and supervised construction of the quay wall, the coastal engineering and dredging elements .
Container ships up to 350m long with 50m wide beams and draughts of 15m will be able to berth at the quay wall.
The main design challenges arose from the extremely weak soils, predominantly soft clays, and the variable hydrological conditions caused by dredging of the canal to allow the big ships to dock. Hamza Associates chairman and founder Dr Mamdouh Hamza says the site had previously been considered 'unconstructable' by several consultants.
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 results. 'This meant the soil risk was transferred to the winning contractor, so we managed to eliminate Clause 12 claims for unforeseen ground conditions, ' says Hamza.
Site investigations were supervised by UK firm, the Geotechnical Consulting Group.
Cone penetration testing with piezocones was carried out, along with high quality sampling from boreholes using hydraulic piston sampling and rotary coring, insitu vane tests and SPTs.
Results, combined with laboratory tests, were used to check design calculations and to determine engineering properties for 3D finite element analyses (carried out using the Flac3D package). Three continuously sampled boreholes were also logged to record a detailed picture of the soil fabric.
Ground conditions comprise 5m of hydraulic fill and dredged silty sands and clays from construction of the east branch of the Suez Canal, 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 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 to be very successful, ' Hamza says. 'Afterwards we knew everything about the ground.'
Conventional design of quay walls usually incorporates sheet piles and tubular piles, he explains, but the higher strength of the clay meant that a different approach could be taken.
Design had to consider not only the enormous operating loads of the 12 massive quayside cranes and 36 gantry cranes but also, in the short term, the effects of forming the 16.5m deep berthing channel in front.
Settlement calculations had predicted 47mm of vertical movement without dredging, which in fact caused heave in the structure to give a total settlement of only 8.5mm.
The quay wall is a retaining-bearing 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.
A continuous 1m thick, 35m deep diaphragm wall provides support along the front face and a similar 10m deep structure runs along the back. The walls have 3m long primary panels and 4m long T-shape secondary panels, the latter connecting with the outer barrettes of each row. Hamza says using concrete rather than steel allowed local materials to be used, saving about US$26M.
Construction of the wall began in January 2000, 200m back from the initial dredging channel. First, two well-point dewatering lines were put down, 13m from the seaward edge and 17m from the land side, to lower groundwater level. Four rows of sand drains running along the wall area were then installed to reduce pore water pressure. Next, a working platform had to be built. Up to 2m was excavated, replaced with sand fill and topped with crushed stone.
Guide walls, up to 1m deep, were built for the walls and the barrettes. In both cases they were formed using hydraulic grabs under bentonite slurry. The T-shaped 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 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 heavy cranes. This reduces the effects of heave and deformation of the structure.
The deck is designed to allow for the effects of the ground conditions, temperature variation and even earthquakes. Precast elements are 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.
The wall and the surrounding ground is heavily instrumented to monitor movements of the structure during construction, dredging and operation of the terminal. On the wall surface, surveying points measure vertical and horizontal movements; vibrating wire strain gauges monitor axial strains and stresses in the barrettes at four levels; sliding micrometers monitor axial deformation with depth; and inclinometers measure horizontal movement on the barrettes.
For the ground, surface settlement points measure vertical movement across the wall, multiple point deep extensometers measure the distribution of vertical movement with depth at the front and back of the wall, horizontal movement is measured by inclinometers and groundwater pressure by multiple point vibrating wire piezometers.
In the aggressive environment, reinforcement corrosion is also a concern. An anode ladder system is used to monitor the penetration of chloride ions and an embedded reference electrode system measures the potential of the reinforcement.
Dredging by a joint venture of Boskalis, Ballast Nedam, Jan DeNul and Hyundai began in March 1999. Work involved forming the inland channel from the sea, running roughly parallel to the east branch of the canal; the berthing channel at the quay wall site; a ship turning circle and a short cut to the east branch to the south.
All dredging and coastal work, including construction of a 2.3km long breakwater, coastal protection and dredging of an approach channel, is now complete. Construction of the container terminal will begin soon, with the first ships due to dock in the first quarter of 2004.