## 3 Materials and Equipment  
### Materials and Laboratory Testing  
The materials used in the experiment were clays, sands, crushed gravels, and composite geotextiles. The clay was sourced from near the Gunsan Train Station, South Korea. Geographically, Gunsan is situated near the coast, approximately 200 km southwest of Seoul (see Figure 1). Table 1 shows the properties of the clay sample obtained from the laboratory testing for soil classification. The soil was then classified in the Unified Soil Classification System (USCS) as inorganic clay (CL). The compaction test (Korean Standard, KS F 2312) showed that the clayey soil had an optimum moisture content (OMC) of 14.5% and a maximum dry unit weight of 17.75 kN/m\({}^{3}\). The clayey soil used during the experiment had two normal moisture contents (NMC): 30% (NMC 1), during the mold model test, and 35% (NMC 2), during the box model test. The soft clay will, therefore, be referred to as the NMC clay in the rest of this paper. The particle-size analysis (Korean Standard, KS F 2302) of the clayey soil is shown in Figure 3, wherein 97% is finer than 74 mm (No. 200 sieve). Another material used in this experiment was sand. The sand was tested as the basis for comparison because it has proven to be an effective backfill material and is also a desirable embankment material [5]. In this experiment, both loose sand and dense sand were used. For the mold model test, loose sand was directly placed in the mold, without compaction, while dense sand was compacted by hammering the sides of the mold. However, compaction in the box model test was different. The air pluviation method [10] was conducted using the sand sample. The falling height, when the sand was dropped, varied from 10 to 100 cm. The relative density of 50% was then obtained at a falling height of approximately 34.6 cm, with a corresponding unit weight of approximately 14.42 kN/m\({}^{3}\). Hence, to achieve dense sand in the box model experiment based on the results of the air pluviation method, the sand sample will be poured into the box with a constant falling height of 80 cm. The properties of sand used in this study are tabulated in Table 2. The sand had a specific gravity, Gs, equal to 2.715. The sand was classified, using the USCS, as poorly-graded sand (SP), whose particle sizes were finer than the No. 20 sieve, but were generally retained in the No. 40 sieve (see Figure 3). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **USCS** \\ **Class.** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Specific** \\ **Gavity, Gs** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Percentage** \\ **Passing** \\ **\#200 Sieve** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Liquid** \\ **Limit, LL** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Plastic** \\ **Limit, PL** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Plasticity** \\ **Index, PI** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Max Dry Unit** \\ **Weight, kN/m\({}^{3}\)** \\ **Weight, kN/m\({}^{3}\)** \\ **Content (OMC)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Optimum** \\ **Moisture** \\ **NMC 1** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Normal Moisture** \\ **Content (NMC)** \\ \end{tabular} } \\ \hline \multirow{2}{*}{
\begin{tabular}{c} **CL** \\ \end{tabular} } & \multirow{2}{*}{**2.637**} & \multirow{2}{*}{**97\%**} & \multirow{2}{*}{**45.0\%**} & \multirow{2}{*}{**23.6\%**} & \multirow{2}{*}{**21.4\%**} & \multirow{2}{*}{**17.75**} & \multirow{2}{*}{14.5\%} & \multirow{2}{*}{30\%} & \multirow{2}{*}{35\%} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Clay Properties. Figure 2: The flow diagram of the experimental study. Crushed gravel is also used in this experiment to reinforce the clayey soil. The crushed gravel was classified, using the USCS, as poorly graded gravel (GP). A specific gravity test was done for the gravel sample based on AASHTO T 85 and ASTM C 127.