Steel or concrete walls are installed at the toe of an embankment on loose and saturated sand for the reduction of embankment settlement caused by liquefaction. For example, the partially floating sheet-piles (PFS) method is a steel wall structure consisting of partially floating sheet-piles and end-bearing sheet-piles for embankment reinforcement. Although this structure has gaps between the floating sheet-piles, the behavior of liquefied sand in the gaps is important for the application of this structure on coastal embankments. However, the behavior of liquefied sand near underground structures is not clear. In this study, a series of experiments were conducted to confirm the behavior of liquefied sand near and between underground structures. Twelve experimental tests were conducted by changing the size of the gaps between the structures and weight of the embankment. These experiments allowed the displacement and direction of movement of liquefied sand near underground structures during an earthquake to be determined for each condition. The relationships between the embankment settlement and the conditions (gap size, weight of the embankment) were also quantified. For example, the larger the gap became, the greater was the displacement of the liquefied sand, and thus, the greater was the embankment settlement. In addition, the author proposed a 2D numerical analysis model to evaluate the deformation of 3D underground structures with gaps between walls.
As many coastal embankments are constructed on loose and saturated sand, there is a risk that they will be damaged by liquefaction of the foundation during an earthquake. As a countermeasure, steel or concrete walls are installed at the toe of the embankment to reduce the embankment settlement. Because this underground structure has the same cross section along the embankment direction, 2D finite element method (FEM) was often used to design the specifications of the walls (Fujiwara, 2017).
Nowadays the partially floating sheet-piles (PFS) method, a steel wall structure consisting of partially floating sheet-piles and end-bearing sheet-piles, is proposed as one of the river embankment countermeasures against soil settlement due to liquefaction and consolidation, as shown in Fig. 1. In the case of the 2016 Kumamoto Earthquake, according to a field survey, damage was suppressed on a river embankment where the PFS method had been applied (Otani, 2017).
