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Breaking records

Spotlight

Loadtest has created a new world record for static load testing of piles on a new cable-stayed bridge in South Korea, achieving a loading force of 210,000kN.

When complete, the Incheon Bridge will link Incheon Inter national Airport with the New Songdo City. It is being constructed and financed through a Public Private Finance Initiative for concessionaire Koda, a special-purpose company headed by contractor Amec.

The central section of the 12km link is a steel box girder cable-stayed bridge that has five spans, with a centre span of 800m and a clearance height of 74m.

A joint venture company, headed by Samsung Corporation, has the contract to design and construct the bridge. It proposed four preliminary test piles along the route in water between 5m and 14m deep, and Loadtest was contracted to fit these test piles with Osterberg cells (O-cells) to perform a static bi-directional load test.

The piles were constructed using permanent casings installed through the sea bed into the soft rock to depths of between 38m and 48m, with boring carried out down to a maximum level of -56m using reverse circulation drilling. Up to nine levels of strain gauges and three sections of embedded telltales were incorporated into the test piles.

The patented bi-directional Osterberg Cell testing technique involves casting specially made sacrificial jacks (O-cells) within the pile at a specific depth, at which equal capacity exists above and below.

The O-cell derives all reaction from within the soil and/or rock itself.

Working in two directions, upward against skin friction and downward against skin friction and end bearing, the O-cell automatically separates the resistance data.

Load testing with the O-cell continues until one of three things happens: skin friction is fully mobilised, ultimate end bearing capacity is reached or the maximum O-cell capacity or ram travel is obtained.

After the four load tests at the Incheon Bridge had been carried out, loading continued beyond the planned maximum loads.

Three of the tests exceeded the previous world record of 163,000kN set by Loadtest in 2003, with the new world record of 279,000kN exceeding the old one by 116,000kN.

www. loadtest. co. uk

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