## 2 Materials and Methods
### Compacted Specim Preparation  
The compaction moisture content, 46.5%, was determined by [PERSON] and [PERSON] [21] through trial tests based on the relative compaction of the clay. The clay with no polyurethane was compacted with an initial void ratio of 1.06, while the polyurethane-clay was compacted with the same effort and had an initial void ratio of 1.44. Hence, a third compacted clay specimen was molded with an initial void ratio of 1.44. The difference in the initial void ratio of the first compacted clay with compacted polyurethane-clay was attributed to the difference in specific gravity of the two loose specimens, clay and  
\begin{table}
\begin{tabular}{c c c c c} \hline
**PU Content** & **Dried Clay** & **PU** & **Dried Clay and PU** & **Water** \\ \hline
0\% & 68.26 kg & 0.00 kg & 68.26 kg & 31.74 kg \\
3\% & 66.22 kg & 2.04 kg & 68.26 kg & 31.74 kg \\ \hline \end{tabular}
\end{table}
Table 1: Sample mix proportions [21].  
polyurethane-clay. Table 2 shows the soil index property of the two loose specimens. It can also be observed that the grain size of polyurethane-clay is larger than that of clay. The difference in grain size between polyurethane-clay and clay also affect its resistance to volume changes, such as shrinkage, as inferred by [PERSON] and [PERSON] [22].  
The compaction efforts applied to both compacted clay specimens can be linked to a study by [PERSON] and [PERSON] [29], which predicted the hydraulic conductivity of compacted clay based on the applied compaction effort. This connection is relevant, since the study used the same type and origin of clay specimens. Similarly, [PERSON] and [PERSON] [21] found that the hydraulic conductivity of a compacted clay specimen with an initial void ratio of 1.06 matched the hydraulic conductivity estimated in the study of [PERSON] and [PERSON] [29]. Consequently, the estimated compaction effort for the compacted clay specimen with an initial void ratio of 1.06 and for the compacted polyurethane-clay was determined to be 600 kN-m/m\({}^{3}\), corresponding to the standard Proctor compaction effort.  
To differentiate the three compacted specimens, the following designations were adopted: the compacted clay with an initial void ratio of 1.06 is referred to as the compacted clay layer (CCL), while the compacted clay with an initial void ratio of 1.44 is termed the clay layer (CL). The polyurethane-clay specimen compacted with the same effort as CCL but having the same initial void ratio as CL is referred to as the compacted polyurethane-clay layer (CPCL). Table 3 summarizes the compaction efforts applied to the specimens, all molded within cylindrical acrylic molds with an inner diameter of 66 mm and a height of 20 mm. The three specimen types--CCL, CL, and CPCL--were also utilized in the study of [PERSON] and [PERSON] [22]. Their findings revealed that incorporating polyurethane into the loose specimen increased the grain size, which improved resistance to shrinkage compared to specimens without polyurethane, regardless of the initial void ratio. Among the three specimen types, CPCL exhibited the greatest shrinkage resistance, as inferred by [PERSON] and [PERSON] [22].