Incheon Bridge
The planned causeway and cable-stayed bridge structure to link the Incheon International Airport with the New Songdo City project got off to a record breaking start, with the static load testing of several preliminary piles along the proposed route. Load-testing for the 2.4 m to 3.0 m diameter bored piles, to a planned maximum loading force of 210,000 kN was completed early 2005.
Project: Incheon Bridge
Location: Incheon, South Korea
Main Contractor: Samsung Corporation
Foundation Contractors: Daewang E & C Company
Located 10 km south of the Yeongjong Bridge, which has been in operation since November 2001, this signature bridge project will be constructed and financed through a Public Private Finance initiative. The concessionaire, KODA Development Co., Ltd. (KODA), a special purpose company, with 51% AMEC and 49% Incheon City ownership, will operate and maintain the bridge for 30-years period, after which time it would be transferred to the Korean Authorities. The total bridge length, including cablestayed bridge, approach bridges and viaduct bridges is approximately 12 km. The steel box girder cable-stayed bridge has five (5) spans, with a maximum center span length of 800 m and a clearance height of 74 m for ship passage. The bridge has a 33.4 m wide road deck to accommodate three (3) lanes of traffic in each direction.
A joint venture company, headed by Samsung Corporation has been awarded the contract for this project; including detailed design and construction. In order to reduce the construction period, the contractor has adopted a fast-track procedure, in which construction begins on one phase after it is approved, while the design work and construction planning is still in progress for the next phase.
Four preliminary test piles were proposed along the route in water between 5 – 14 m deep. These test piles were to be fitted with Osterberg cells (O-cells) to perform the static bi-directional load test as trying to achieve these loads with kentledge or anchor piles is impractical. Construction of the piles was with a permanent casing through the sea bed and into the soft rock, at 38-48 m, boring was carried out down to a maximum level of –56 m using reverse circulation drilling. Up to 9 levels of strain gauges and 3 sections of embedded telltales were deployed. An additional advantage of bi-directional testing is that concreting up to the top of the pile is not necessary, and for this project the concrete was brought up to the level of the sea bed.
Bi-directional load test arrangement:
In order to achieve the test loads required, the only method available was the use of the patented bi-directional Osterberg Cell testing technique in which specially made sacrificial jacks (O-cells) are cast within the pile itself at a specific depth at which equal capacity exists above and below.
The O-cell® is a hydraulically driven, calibrated, sacrificial jacking device installed within the foundation unit and derives all reaction from within the soil and/or rock system 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. By virtue of its installation within the foundation member, the O-cell® load test is not restricted by the limits of overhead structural beams and tie-down/anchor piles.
Load testing with the O-cell® continues until one of three things occurs: skin friction is fully mobilised, ultimate end bearing capacity is reached or the maximum O-cell® capacity or ram travel is obtained. Each O-Cell® is specially instrumented to allow for direct measurement of the O-cell's expansion. By also measuring the top of shaft or pile head movement and compression, the downward movement is determined.
O-cells range in capacities from 0.7 MN to 27 MN. By using one or multiple O-cells on a single horizontal plane, the available test capacity can be increased to more than 220 MN. By utilizing multiple cells on different planes, distinct elements within a shaft or pile can be isolated for testing.
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