Interpretation of the mechanical behavior of embankments having various compaction properties based on the soil skeleton structure

Abstract

After the Hanshin Awaji Earthquake disaster, the seismic resistance of embankments was evaluated, and design principles were changed from specification-based to performance-based. However, compaction properties and the mechanical behavior of compacted soil were not sufficiently considered in the Manual of Highway Earthworks on Embankments.The first objective of the present study is to reproduce the mechanical behavior of three embankment materials having different compaction properties. A series of triaxial compression tests and oedometer tests is carried out. The mechanical behavior is reproduced by the SYS Cam-clay model and the influence of compaction on the mechanical behavior is interpreted based on the soil skeleton structure. The second objective is to evaluate the seismic stability of the embankment, which depends on the compaction properties of the embankment material, using GEOASIA, a soil–water coupled finite deformation analysis code.The primary conclusions are as follows. (1) Through the triaxial tests, the maximum deviator stress increases as the degree of compaction, Dc, increases. However, the trends in the increase differ depending on the material. (2) Based on one-dimensional consolidation tests, the compression curve is approximately a straight line with a large vertical effective stress. In the present study, a greater maximum dry density corresponds to less compressibility and a lower compression curve. (3) The mechanical behavior of each material is reproduced by the SYS Cam-clay model using one set of material constants for each material and representing the differences in Dc by different initial conditions for the structure and overconsolidation. An increase in Dc causes the decay of the structure, as well as the accumulation of overconsolidation. In the case of material A, the decay of the structure and the loss of overconsolidation occur quickly, whereas in the case of material C, the decay of the structure is slight and the loss of overconsolidation is moderate. (4) The seismic response analysis reveals different deformations of the embankment for different materials, even for the same Dc. The seismic stability of the embankments was increased by increasing Dc. Materials, such as material A, that have fast decay of the structure and fast loss of overconsolidation produce embankments with high seismic stability.