2.2.3. Incheon Region

The Incheon region soil analyzed from four sites shown in Table 1 had the specific gravity, plastic limit, liquid limit, and plastic index of 2.693–2.713 (avg. 2.703), 12.48–22.74% (avg. 16.48%), 24.86–38.34% (avg. 30.62%), and 11.84–16.78% (avg. 14.15%), respectively. The sand particle content,

silt particle content, and clay particle content for the Incheon region soil were 4.59–8.78%, 79.38–84.41%, and 10.79–14.42%. The activity with a range of 1.04–1.22 and average of 1.13 lies in the normal area, as shown in Figure 6. The consolidation properties were analyzed with C<sup>c</sup> = 0.167–0.406 and C<sup>k</sup> = 0.246–0.628 during the oedometer test, and C<sup>c</sup> = 0.204–0.493 and C<sup>k</sup> = 0.380–0.791 during the CRS test, as shown in Figure 7.

**Figure 6.** Physical properties of the Incheon region soil: (**a**) Plasticity chart; (**b**) Activity chart.

**Figure 7.** Consolidation properties of Incheon region soil: (**a**) liquid limit (LL)-compression index (Cc); (**b**) liquid limit (LL)-permeability change index (Ck).

The Incheon region soil had lower liquid and plastic limits than the Busan and Gwangyang region soils. The liquid limit was 30.12% less than that of Busan clay and 25.15% less than that of the Gwangyang clay. The plastic index was less than 17.5 compared to the Busan and Gwangyang clays. The results of the oedometer test show that Incheon clay exhibited a C<sup>c</sup> = 0.31 and C<sup>k</sup> = 0.246–0.628, which were less than those of the Busan and Gwangyang clays. That is, the Incheon region soil clearly showed low plasticity, small compressibility, and large permeability than the Busan and Gwangyang clays.

Furthermore, the Incheon region soil had different physical and compressive properties that were separated by the criteria of LL = 30% compared to the Busan and Gwangyang clays (LL = 60%). The ic-c and ic-d specimens with LL ≥ 30% had large fine particles, large compressibility, and small permeability compared to the ic-a and ic-b specimens with LL < 30%. Therefore, the Incheon region dredged soil can be separated reasonably using the criteria of liquid limit (LL = 30%). The clay with LL < 30% was named the Incheon-L marine clay and the clay with LL ≥ 30% was named the Incheon-H

marine clay. Engineering properties of the marine soft soil were classified by liquid limits and are summarized in Figure 8.

**Figure 8.** Engineering properties for the classified marine soft soil by liquid limits.
