# Effect of Fines Content on the Compression Behavior of Calcareous Sand
## 2 Materials and Methods  
### Test Materials  
The calcareous sand used in this study was sourced from an island reef in the South China Sea. Prior to testing, the calcareous sand was cleaned and dried. Then, it was sieved using nine different sieve layers: \(<\)0.075 mm, 0.075-0.01 mm, 0.1-0.15 mm, 0.15-0.25 mm, 0.25-0.355 mm, 0.355-0.5 mm, 0.5-1 mm, 1-2 mm, and 2-5 mm, to obtain calcareous sand particles of different sizes (see Figure 1). The large particle group of in situ calcareous sand (particle size \(>\) 2 mm) retained some skeletal forms of marine organisms, containing numerous irregular particles with branch-like and angular shapes. As the large particle group constituted less than 5% of the total mass, to minimize random errors, the study followed established practices by removing calcareous gravel larger than 2 mm, and focused on particles smaller than or equal to 2 mm. The particle size distribution curve of the remaining material is shown in Figure 2. The calcareous sand used in this study was unconsolidated granular material, with its detailed physical parameters provided in Table 1. The sample contained almost no fine particles smaller than 0.1 mm, with a uniformity coefficient of 2.5 and a curvature coefficient of 0.96, classifying it as poorly graded sand.  
Figure 1: Calcareous sand particles with different grain sizes (same magnification).  
The original calcareous sand was crushed into fine particles with diameters ranging from 1 to 75 \(\upmu\)m, and its particle size distribution curve was determined using the hydrometer method (Figure 2). Subsequently, pure sand and the crushed fine material were uniformly mixed in varying dry weight ratios of 10:0, 9.5:0.5, 9:1, 8.5:1.5, 8.2, 7:3, and 6:4, resulting in seven soil samples: X-0, X-5%, X-10%, X-15%, X-20%, X-30%, and X-40%. The relative density tests were conducted in accordance with the \"Standard for Soil Test Methods\" (GB/T50123-2019) [27]. The minimum dry density was determined using both the funnel method and measuring cylinder method, with the smaller value (from the measuring cylinder method) selected. For the maximum dry density, the vibrating hammer method was used, employing a 250 mL compaction cylinder. These tests yielded the minimum and maximum dry densities of the seven soil samples, and the corresponding maximum and minimum void ratios were calculated using Equations (1) and (2) [27]. Table 2 presents the key physical parameters of these seven calcareous sand samples.  
\[e_{\text{max}}=\frac{\rho_{\text{w}}G_{\text{S}}}{\rho_{\text{dmin}}}-1 \tag{1}\]  
\[e_{\text{min}}=\frac{\rho_{\text{w}}G_{\text{S}}}{\rho_{\text{dmax}}}-1 \tag{2}\]  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Test Material** & \(\mathbf{G_{\text{s}}}\) & \(\mathbf{d_{50}}\) (mm) & \(\mathbf{d_{10}}\) (mm) & \(\mathbf{d_{30}}\) (mm) & \(\mathbf{d_{60}}\) (mm) & \(\mathbf{C_{\text{u}}}\) & \(\mathbf{C_{\text{c}}}\) \\ \hline Calcareous sand & 2.78 & 0.69 & 0.32 & 0.50 & 0.81 & 2.5 & 0.96 \\ \hline \end{tabular}
\end{table}
Table 1: Basic physical parameters of the test material.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Soil Samples** & \(\mathbf{f_{\text{c}}}\) & \(\mathbf{G_{\text{s}}}\) & \(\mathbf{d_{50}}\) (mm) & \(\mathbf{\rho_{\text{dmin}}}\) (g/cm\({}^{3}\)) & \(\mathbf{\rho_{\