# Effect of Fines Content on the Compression Behavior of Calcareous Sand
## 3 Results of Compression Tests
At low stress levels, the coefficient of volumetric compressibility is strongly influenced by the fines content, whereas this effect diminishes under higher stress levels. Figure 7b describes the relationship between the coefficient of volumetric compressibility and fines content under vertical stresses of 100 kPa, 200 kPa, 400 kPa, 800 kPa, and 1600 kPa. It is clear that the compressibility of Sample E and F (with \(f_{\rm{c}}\) = 15% and 20%, respectively) is significantly higher than that of other samples. For the calcareous material studied, total compressibility is highest when the fines content ranges from 15% to 20%, indicating that the calcareous silty sand is in a transitional state within this range. Effects of Fines Content on Compression Characteristics of Calcareous Sand at Different Initial Relative Density States  
Test Series II compared calcareous silty sand with a fine particle content of 10% (soil sample X-10%) to clean sand, examining the impact of adding fine particles on the compressibility of calcareous sand at various initial relative densities (low-density \(D_{\rm{r}}\) = 30%, medium-density \(D_{\rm{r}}\) = 50%, high-density \(D_{\rm{r}}\) = 70%). The soil sample X-10% was selected based on the results from Test Series I, which demonstrated that when the fines content reached 10%, the effect of fine particle addition on the compressibility of calcareous silty sand became significantly more evident. Figure 8 presents the variation in the coefficient of volumetric compressibility (\(m_{\rm{\tau}}\)) with axial load for both clean sand and calcareous silty sand (\(f_{\rm{c}}\) = 10%) across three different relative densities. The figure demonstrates that, regardless of whether the sand is clean or mixed, a higher initial relative density leads to a lower volume compression coefficient and reduced compressibility. The results further reveal that, under low- and medium-density conditions, the addition of fine particles increases the coefficient of volumetric compressibility, while under high-density conditions, it decreases the coefficient. Furthermore, the differences in the coefficients of volumetric compressibility among the silty sand Sample K, C, and L (\(D_{\rm{r}}\) = 30%, 50%, 70%) are significantly greater than those among the clean sand Sample I, A, and J (\(D_{\rm{r}}\) = 30%, 50%, 70%). For example, under a vertical load of 400 kPa, the coefficient difference of volumetric compressibility between clean sand Sample I (\(D_{\rm{r}}\) = 30%) and J (\(D_{\rm{r}}\) = 70%) is 0.8 \(\times\) 10\({}^{-5}\)/kPa, while the difference between mixed sand Sample K (\(D_{\rm{r}}\) = 30%) and L (\(D_{\rm{r}}\) = 70%) is 1.8 \(\times\) 10\({}^{-5}\)/kPa. Figure 6: Vertical compression deformation with varying fines contents under different levels of axial load (\(D_{\rm{r}}\) = 50%). This phenomenon indicates that the addition of fine particles amplifies the compressibility differences between samples with varying initial relative densities. Figure 7: Variation of the coefficient of volumetric compressibility with varying fines contents under different levers of axial load (\(D_{\text{r}}=50\%\)).