FOUNDATION DESIGN for South Korea's new Taegu football stadium has been carried out by WS Atkins.
Taegu Stadium is part of a comprehensive development programme across South Korea to provide top-level facilities for the 2002 football World Cup finals which it is co-hosting with Japan.
Sited about 10km south-east of the city, the stadium will seat 70,000 spectators beneath a lightweight steel roof comprising two crescentshaped steel frames covered with PTFE fabric.
Each steel frame, which spans 280m, is supported on reinforced concrete towers at each end of the stadium.
Taegu City is funding and managing the project, with site supervision by LG Engineering. A joint venture of four major Korean construction firms led by the Samsung Corporation is building the stadium.
Work began in late 1997 and is due to finish in mid-2001. Seoul-based architect Idea Image Institute is providing architectural services as well as the structural design of the stadium itself.
WS Atkins was responsible for the design of the roof, the towers and foundations.
Ground conditions consist of up to 4m of made ground comprising medium dense to very dense silty sandy gravel which is underlain by a thin layer of very dense residual soil.
Bedrock consists of a slightly metamorphosed non-fissile mudrock which is highly weathered at the top.
A number of foundation options were considered, including raft foundations cast directly on rock, vertical bored piles, raked bored piles and barrettes, as there was uncertainty about the suitability of the bedrock as a founding stratum. There was also great concern about its ability to resist the large component of horizontal thrust acting on the tower foundations.
And as South Korea has a moderate seismic risk, the regional earthquake coefficient of 0. 12 was used in design.
Additional ground investigation revealed that the bedrock at each tower location was in a better condition than anticipated. As a result, it was decided that the most efficient foundation design would be a raft founded on the fresh to slightly weathered rock, although additional measures were required to resist overturning forces at foundation level.
To minimise deflection of the roof support towers, particularly during extreme load cases such as high winds, it was also decided to use an 'active tie-down system'using prestressed rock anchors.
While use of permanent rock anchors is not unusual in Korea, especially in Seoul where buoyancy forces in deep basements are frequently resisted by anchors, David Puller and Christopher Palanque ofWS Atkins said the working load at Taegu of 150t was unusually high for South Korea.
Each anchor comprised 12, 15. 2mm strands with a fixed anchor length of 8. 5m and free anchor lengths varying between 13. 5m and 17. 5m. Double corrosion protection was provided over the free length using individual strand encapsulation as well as a single corrugated PVC sheath. A single layer of corrosion protection over the fixed anchor length was provided by a corrugated sheath.
Sheath leakage tests were carried out at every anchor location following installation.
Before working anchors were installed, a trial anchor was load tested to failure. This was designed to test all stages of the process including the manufacture of individual anchor components and the drilling, grouting and stressing.
Long-term anchor performance has been monitored using three permanent load cells installed at each of the four tower bases. Initial survey readings with the most of the roof dead-weight acting, indicate deflections in the region of12mm, which is below predicted values.