LIFELINE UPGRADE FOR A WHARF IN SOFT GROUND

摘要

A section of the existing wharf and reclamation of the Kings Wharf in Suva, Fiji has been selected for an upgrade to serve as a lifeline wharf in the event of an earthquake. The reclamation is retained by a 16 m deep sheet pile wall, tied back near the top and supported at the toe by a rock bund. The wharf deck is supported on 760 mm diameter prestressed hollow core piles and is connected to the reclamation by a series of bridging decks. The geology consists of a large depth (40 m) of soft soils. With excessive horizontal movements known to have occurred during construction, and with the knowledge of marginal stability from limiting equilibrium slope stability analyses, more sophisticated modeling was applied to better understand the stability concerns. The finite difference computer program FLAC was selected for this purpose. The objectives were to assess the stability of the existing wharf configuration under both static and seismic loading, and evaluate a proposed soil-cement improvement. The cement treatment is to be applied to a soil block 30-40 m deep and 14.5 m wide, immediately behind the existing sheet piles. The FLAC analyses showed that the cement treated block did address the deep-seated stability problem. However this also highlighted the effects of shallower movements in the rock toe bund causing structural distress to the piles. The soil-cement improvement was a necessary rehabilitation measure for limiting the displacements in the deep soft soils. Additional measures (reduction in rock bund height and infilling the hollow core piles) to address more structurally orientated shortcomings were also necessary.