大水深護岸の変形解析

Abstract

This paper is concerned with the predicted performance of an offshore airportfill to be built on the bed of soft alluvial clay underlain by very thick strata of ple-istocene clays. Coupled stress-flow analysis using the method of finite elements areperformed, with emphasis on predicting the behaviour of the seawall and the nearbyabutment for the access bridge. Elastoplastic and creep properties of the Quaternaryclays is considered in the analysis procedure in a consistent way, through the im-plementation of a plane-strain elasto-viscoplastic constitutive model. The predictedperformance emphasizes the importance of the long-term consolidation of the pleisto-cene clays, in terms of post-construction deformation, as compared with the behavi-our of the overlying soft alluvial clay that is treated partly with columns of denselycompacted sand (SCP) and more extensively with vertical sand drains (SD). It isshown that the vertical stress tends to concentrate into the SCP-treated region ad-joining the more compressible SD-treated region, and that such stress concentrationaccounts for the peak occurring in the profile of compression of the pleistoceneclays along the axis of the access bridge. It is also shown that the initially over-consolidated pleistocene clays undergo yielding in their upper part, along with thegradual dissipation of excess porewater pressures, and that the front of yielding pro-gresses downwards with time. Such delayed yielding is shown to be predominantwell after the end of construction and is accompanied by the delayed, laterally out-ward deformation of the pleistocene clays. This behaviour of the undersea clays iscontrasted with the behaviour of the crest of the sea wall and the abutment footing, both of which exhibit the inward lateral movements with time, in general accord-ance with the settlement profile of the undersea soils along the axis of the accessbridge.