Case study on progressive displacement method constructed in the south coastal area in Korea

When embankments or dykes are built on weak marine clayey soils, it is necessary to ensure that stability is considered during construction and in use also. An embankment shall also be practically free from settlement to limit maintenance costs. One way of satisfying these conditions on stability and permissible settlement is to replace the compressible weak soil with gavel or blasted rock. Replacement can be performed by excavation and backfill, or by progressive displacement. Progressive displacement method leads to lower costs comparing to other ones during construction as well as maintenance. Many geotechnical engineers in Korea, for these reasons, have been adopted progressive displacement in the designing of reclamation of soft marine clay in the costal area. However, there are many limitations still unknown. Most of these limitations, especially concerning about the determination of the replacement depth, are related to the thickness of soft layer. Other factors are related to the material properties such as cohesion and unit weight of marine clay, internal angle of resistance and unit weight of blasted rock, geometrical properties of the embankment such as slope, height and width, the rate of construction. laboratory testing method for seeking of optimum soil parameter, and in-situ boring techniques, etc. There are some kinds of theoretical and experimental equation to determine the replacement depth, but they do not fit to all kind of soil conditions. This paper presents the experimental results to determine replacement depth on the basis of in-situ boring datum obtained from constructed site located in the south coast in Korea. Then, numerical simulations, using CRISP FEM code, are performed.