Investigations of the Residual Settlement of Reclamation Dikes and its Prediction Mmethods for the Introduction of Performance Based Design to the Maintenance of Reclamation Dikes

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In the case of Ariake reclamation dike (Saga Pref.), because there was no local difference in both the soil layer composition and the soil properties of the foundation ground, a local difference was not recognized for the residual settlement behavior due to the wave dissipating concrete block establishment. But a local remarkable difference was seen for the ground subsidence in the drought in 1994. On the other hand, in the case of Yokoshima reclamation dike (Kumamoto Pref.) because both the soil layer composition and the soil properties of the foundation ground greatly varied in the area, the difference in the local settlement tendency was remarkable.The following main results about the mechanical properties of Ariake clays were obtained : (1)The Hvorslev's strength parameters of Ariake clays were naturally dependent on grain size distribution. (2)The irreversibility ratio (∧) of Ariake clays was in the range of 0.6〜0.8 and was independent on both grain size distribution and plasticity index. (3)The compression index (C_c) of Ariake clays was strongly dependent on the natural void ratio. (4)The consolidation yield stress (p_c) obtained from the consolidation test using constant rate of strain loading was higher than that obtained from the consolidation test using incremental loading.It was concluded that the consolidation deformation analysis by elasto-plastic finite element method (FEM) was the most suitable as the residual settlement prediction method. However, considering the influence such as groundsubsidence at a drought, the complexity of the soil properties of the foundation ground and the reliability of the soil test data, and so on, the need and utility of the continuous field observation were strongly suggested after the maintenance of the reclamation dike.