Underwater bridge base building is on schedule

SITE preparation and foundation works are on schedule for the Tsing Ma suspension bridge.

Subcontractors in the Anglo-Japanese joint venture are placing base concrete in the Tsing Yi tower footings and piers on the Tsing Yi island side of the project.

Major excavation for the anchorages and foundations of the two towers has been completed.

On the Ma Wan side, a portion of the batch plant has been commissioned, and form work has started on the first land-side pier between the anchorage and the tower.

The Ma Wan Tower requires underwater site preparation, unlike the Tsing Yi tower. Special concrete caissons were built on a submersible barge, and the barge was sunk until the caissons floated off. The caissons, which are floating in the water nearby, arehollow. When the site for the caissons is complete, they will be sunk and pumped with concrete to within seven metres of the top. This space will take the tower legs.

Joint venture partners Mitsui-Costain are conducting form work operations, including the bending of reinforcing steel.

The slip-forming process for each of the two 206-metre towers is expected to start in mid-April. Each tower base has four concrete placement ''lifts'' to facilitate the process.

By the end of this year, both towers should be in place and the 1.15-metre-diameter main suspension cables will be spun out of 37,000 strands of 5mm wire during 1994 and 1995.