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Fighting the elements

Beating harsh weather conditions was a key factor in the design and construction method used to deliver a long jetty in India's Gujerat state, reports Kris Birkett.

Monsoons and hostile sea conditions have battered a jetty building project nearing completion in the Gulf of Cambay at Gujerat in India. Faced with a meteorological onslaught between mid-May and mid-September every year, the project team minimised exposure to the elements by developing a largely land-based piling operation.

To overcome very shallow inshore coastal waters, the jetty has to extend 2.4km from the shore to deep waters beyond the inter-tidal zone. The piled concrete structure, for client Chemical Port Terminal Company - a consortium of chemical, petro-chemical and fertiliser industries - is designed to handle 1.8Mt of liquid cargo a year, delivered by tankers of between 6,000t and 40,000t dead-weight.

Work was let to main contractor Kvaerner Construction under a £50M design and build contract. The project includes delivery of marine structures, berthing and mooring dolphins, with interconnecting walkways, telecommunications, gas detection and fire-alarm systems. There is also a 30m by 17m service platform and a control building at the end of the jetty, with eight marine loading and unloading arms.

To accommodate high tidal ranges and extreme wave conditions caused by the south west monsoon winds, the mooring point of the structure stands 20m above low tide. Wrapped in extra layers of corrosion resistant plating, the driven steel piling penetrates 24m into the seabed.

Three columns of piles support the jetty decking. Transverse pile capping beams were pre-cast as open troughs for in-situ cast reinforced concrete. The deck itself is made of solid precast longitudinal tie beams. Steel pipe trusses flank a raised concrete roadway. Pipe has so far been laid in just one, leaving scope for expansion in handling capacity.

Construction started in September 1997. High cost of marine plant and its vulnerability to the weather drove the contractor to operate as much as possible from shore. For the first 1.6km across shallow waters, more than 450 concrete bored piles were installed by locally-based sister company, Kvaerner Cementation India, using a walking gantry system. A temporary steel road deck was slung between two of the pile columns to allow trucks to deliver precast deck units and construction materials as work extended out to sea.

To speed the project, 370 steel piles up to 60m long were driven into the seabed for the deep-water end of the project, installed by Singapore-based Antar-Koh from a floating barge.

India's high import and customs duties encouraged the Kvaerner team to seek out indigenous supplies wherever possible, guided by the long-established onshore experience of Cementation India as main civils sub-contractor. However, steel for the deepwater piling was shipped from Japan and Germany.

In all, around 3,000 pre-cast deck units and 400 steel trestles were fabricated onshore. The driven piling, between 18mm to 32mm thick, was assembled and prepared from 12m lengths of tubular steel in a huge fabrication yard on site. Sixteen lines of pipework each extend over 2.4km from the loading arms to the onshore storage facility.

With the structural work completed, the final systems are being installed ready for handover before May - and the start of another monsoon summer.

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