Assessment of Lateral Soil Movements under Embankment Loads

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The performances of lateral soil movements under embankment loads are reviewed, and the following conclusions are drawn. (1) The lateral deformation of peaty deposits is accompanied by a substantial degree of partial drainage, even during the embanking stage. (2) The distribution of lateral displacements with depth under the toe of an embankment differs significantly, in accordance with the layered nature of the subsoils. The situations discussed include the marine clay beds overlain by peat or medium dense sand or dry clay crust. (3) The lateral deformability of relatively weak soils, such as peat or organic clay, increases markedly with increasing intensity of embankment loading. Therefore, the lateral-deformation monitoring is very effective for stability control of embankments on such soft foundations. The same thing cannot be expected, however, for relatively strong soils such as overconsolidated clay deposits; this is because they tend to undergo eventual failure without noticeable signs of imminent failure.A new analysis procedure for the soft clay foundation treated with vertical sand drains, is developed. The key idea of the analysis procedure lies in subdividing the treated zone into a special class of finite elements named macro-elements, so that the local water flow towards the sand drains as well as the overall "plane-deformation" of the treated zone may be analyzed in a simple but workable manner. Computationally, this is made possible by adopting the eigen-function of a classic sand-drain problem as the shape function of a basic macro-element, and by taking its spatial average as the unknown pore-water pressure of that macro-element, in combination with the unknown nodal displacements of that element. The validity of the proposed macro-element method is examined and confirmed against the measured performance of a test embankment on a thick bed of marine clay.