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Piling on the pressure

PILING & DEEP FOUNDATIONS CONTRACTS

FOUNDATION CONTRACTOR Bauer Malaysia had to work 24 hours a day, seven days a week to meet a tight deadline on a power station after a major foundation design change five months into the 16-month contract.

The Manjung Power Station is a coal-fired facility in the Manjung Perak district of Malaysia, 260km north west of Kuala Lumpur. The plant is being built on a newly reclaimed 3.25km 2island. It will have three 700MW generators and be supplied annually with 6Mt of coal, delivered to a new deep water jetty.

Client is the Malaysian National Power Supply, with consultant Powergen. Bauer Malaysia was subcontracted to carry out foundation work by the contractor, a consortium of ABB and Alstom Power Plant.

Five months into the contract, it was decided to change from driven to bored piles. Despite this, the schedule was not extended. Bauer had to complete piling and stone column construction in only eight months, with an output of 100 piles a week.

Foundations comprised 3,300, 800mm to 1200mm diameter bored piles to a maximum depth of 74m; 262,000m of stone columns up to 20m deep; and 27,000m 2of 600mm thick cut-off wall. Other subcontractors installed 16,500m 2of1000mm thick diaphragm wall.

Site geology is 8m of loose, unconsolidated sand, over alluvial clayey silt with traces of organic fragments, mainly marine clay to 35m, underlain by medium dense to dense fine to coarse quartz sand to 80m.

Excavation of the bored piles was done in two steps. Temporary casing was installed through the loose sand and then bentonite slurry used to stabilise the borehole walls through the clays and dense sand to final depth.

The work necessitated huge resources. At its peak, Bauer had 50 pieces of equipment on site, including eight BG drilling rigs, 33 crawler cranes, seven excavators, four vibro hammers and eight deep vibrators and 525 people were employed in piling and stone column construction.

Bauer averaged weekly rates of 100 bored piles, 14,400 linear metres of stone columns and 2,040m 2of cut-off wall, to meet the deadline.

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