| Popis: |
Two case histories involving harbour works in a deltaic environment are described in the paper. The mechanisms underlying delta formation and development are outlined first; they involve climate changes, geological processes and human effects. The history of the Llobregat delta, the location of the case histories, is presented. The first case concerns the design and construction of a vertical caisson breakwater. The incorporation of storm wave loading, the description of the geological setting and the bases for stability evaluation are discussed. Special attention is given to the stability of the structure during the construction period when stability issues are more critical. The use of the envisaged observational method was hampered by the limited monitoring data available resulting in a modification of the planned approach. The second case refers to the reconstruction of the Prat quay after a major failure caused by the flow liquefaction of the hydraulically-deposited backfill. Post-failure investigation and analyses identified the need for reducing the liquefaction potential of the backfill and enhancing the undrained shear strength of the foundation clay; preloading was the main ground improvement method selected. The observational method was used to steer the construction activities to ensure an adequate margin of safety. The paper closes with some general considerations of the role of geology, observational method and judgement in the cases reported. |
