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Saturday, October 31, 2009 |
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A mega marine project at the Cape Town Container Terminal
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Source: Graham Moore
The increasing size of container ships visiting the Cape Town Container Terminal has necessitated the dredging of the berth to a depth of -15.5m Chart Datum in order to accommodate the larger vessels. In addition, to ensure that the integrity of the existing container berth quay wall was not compromised and in order to cater for the larger berthing forces, a piled structure needed to be constructed alongside the existing container berth.
Civil marine specialist, Civil & Coastal, in conjunction with our JV partner, has been on site since late 2007 undertaking this berth deepening and quay refurbishment of the Ben Schoeman Dock for client Transnet. Currently
valued at over R900 million, this four year project is due for completion in 2013.
As construction is in a working port, the project is being undertaken in four phases to facilitate uninterrupted mooring of container vessels.
The scope of work includes:
• Dredging the Ben Schoeman basin;
• Piling;
• Precast concrete;
• Ground anchors;
• Quay furniture; and
• Scour protection.
The dredging operation has progressed successfully and is 95% complete. The instability of the existing quay wall led to the decision to install ground anchors in the underlying rock layers to prevent rotation of the wall.
The new piled structure being constructed alongside the existing container berth consists of a row of 150 number 914mm diameter piles, which are being driven parallel to the existing quay at intervals of 6 850mm. The piles are vibrated into the sea bed with a vibratory piling hammer, and once the piles hit hard rock, a pile socket is drilled using a Wirth pile top drill rig. Rebar is then inserted into the pile casing and concrete tremmied into the piles.
Due to construction restraints the need for a precast construction yard was identified. We have set up a precast yard in the harbour and are manufacturing our own precast for this project. Precast panels are placed on top of the row of piles and span between the piles and the existing deck. Once the precast is placed we then perform in-situ concrete casts tying the structure together.
Once the new deck is cast, the installation of new quay furniture follows including bollards, fenders and crane rails. In the areas up against the new quay, scour protection in the form of grout blankets are installed on the sea bed.
Where the ground conditions are not conducive to conventional methods a split deck option will be implemented creating a completely separate structure from the existing quay. 84 number 1 422mm pile against the quay wall will act as a pin preventing the quay wall from slipping out.
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