# Effect of Fines Content on the Compression Behavior of Calcareous Sand
## 3 Results of Compression Tests  
Effects of Fines Content on the Initial Void Ratio and Compression Characteristics of Calcareous Sand  
Test Series I investigated the one-dimensional compression behavior of calcareous silty sand and clean sand at a consistent initial relative density (\(D_{\rm r}=50\%\), medium dense). Figure 4 presents the \(e\)-log \(p\) compression curves for calcareous sand samples with varying fines contents. Figure 5 displays the relationships between the compression coefficient (\(a_{\rm 1-2}\)) and the initial void ratio (\(e_{0}\)) with varying fines contents (\(f_{\rm c}\)). The compression coefficient in this study was examined within a pressure range of100-200 kPa (as shown in Figure 3). Across the fines content range studied (\(0\leq f_{\rm c}\leq 40\%\)), substantial differences in the initial void ratios of the calcareous sand samples were observed. As fines content increased, the initial void ratio gradually decreased from 0.985 to 0.673. This reduction can be attributed to the particle morphology of calcareous sand: the original sand had well-developed angular features and irregular particle shapes that easily interlocked and created voids, resulting in a high initial void ratio. However, as fine particles were added, some of these voids were gradually filled, leading to a decrease in the initial void ratio. As illustrated in Figure 5, the compression coefficient of samples with varying fines content ranged from 0.079 to 0.119. The compression coefficient initially increased and then decreased as the fines content increased. According to the compression classification criteria for soils, Sample A, B, C, and H (\(f_{\rm c}=0\%\), \(5\%\), \(10\%\), \(40\%\)) were classified as low-compressibility soils, while Sample E, F, and G (\(f_{\rm c}=15\%\), \(20\%\), \(30\%\)) were classified as medium-compressibility soils. Notably, the compression coefficient of Sample B (\(f_{\rm c}=5\%\)) was similar to that of the clean sand (Sample A), indicating that the addition \(5\%\) fine particles has a minimal impact on compressibility of calcareous sand. However, the compressibility of Sample C (\(f_{\rm c}=10\%\)) increased by \(18.2\%\) compared to Sample A (as represented by \(a_{\rm 1-2}\)), suggesting that a fines content of \(10\%\) or higher significantly alters the compression coefficient. Figure 6 presents the curves depicting the vertical compression deformation percentages of Sample A-H under varying axial loads as a function of fines content. It is evident that within the considered range of fines content, the calcareous silty sand Sample E (\(f_{\rm c}=15\%\)) exhibits greater vertical strain under all levels of load compared to the other samples. The trend of axial deformation follows a distinct \"\(\cap\)\"-shaped curve, where deformation increases with rising fines content, peaks at 15%, and then gradually decreases. At approximately 15% fines content, the calcareous silty sand enters a transitional phase, during which the sample exhibits the maximum compression deformation. Under an  
Figure 3: Schematic diagram of the relative breakage model. axial load of 1600 kPa, samples with fines contents of 15% and 20% show the maximum compression deformation, reaching up to 5.7%. Particularly at low consolidation stresses (i.e., less than 600 kPa), the influence of fines content on the compression performance of calcareous sand is more pronounced. Figure 4: \(e\)-log \(p\) curves for calcareous sand samples with varying fines contents (\(D_{\rm r}\) = 50%). \(e\)-vol ratio. Figure 5: The relationship between compression coefficient and initial void ratio of calcareous sand with varying fines contents (\(D_{\rm r}\) = 50%). Figure 7 illustrates the variation of the coefficient of volumetric compressibility (\(m_{\rm{\tau}}\)) for Sample A-H as a function of fines content (\(f_{\rm{c}}\)) under various axial loads. From Figure 7a, it is observed that the coefficient of volumetric compressibility of each sample decreases with the increase in axial load.