# Effect of Fines Content on the Compression Behavior of Calcareous Sand
## 6 Conclusions  
In this study, the one-dimensional compression behavior of clean sand and calcareous silty sand with varying fines contents was investigated. The effects of fines content and initial relative density on compression and particle breakage characteristics were examined. Additionally, the intrinsic mechanisms of how fines content affects the compressibility behavior of calcareous sand were analyzed from a microstructural perspective. The main conclusions are summarized as follows:  
1. Under identical initial relative density conditions (\(D_{\text{r}}=50\%\)), the initial void ratio of calcareous silty sand samples decreased progressively with the increase in fines content. The compression coefficient (\(a_{1\cdot 2}\)) of these samples ranged from 0.079 to 0.119, showing a pattern of initial increase followed by a decrease with the increase in fines content, indicating a transition from low-compressibility soil to medium-compressibility soil, and eventually back to low-compressibility soil. 2. Under the same gradation and density conditions, the addition of 5% fines had minimal impact on the compressibility of calcareous sand. However, when the fines content reached 10% or more, the compression coefficient underwent significant changes. 3. In the initial stages of adding fines, the relative breakage of calcareous sand significantly increased, especially the Br value of silty sand Sample C was three times that of clean sand Sample A. 4. As fines content increased, the volumetric coefficient (\(m_{\text{v}}\)) of calcareous sand samples showed a tendency to initially increase and then decrease. This behavior is attributed to two factors as follows: first, the reorganization of particle arrangement influenced by inter-particle contact, and second, the volume reduction caused by particle breakage. As fines content rises, the microstructure of calcareous silty sand shifts from coarse particle-to-particle contact to fine particle-to-particle contact. The threshold fine content (\(f_{\text{c-th}}\)) reflecting changes in the compressibility of calcareous silty sand is approximately 15-20% at medium-density (\(D_{\text{r}}=50\%\)). 5. The addition of fine particles exacerbates compressibility differences between calcareous sands with varying relative densities. The threshold fines content (\(f_{\text{c-th}}\)) for calcareous sands with different relative densities also varies. In comparison to medium-density samples, \(f_{\text{c-th}}\) appears earlier in high-density samples and later in low-density samples. **Author Contributions:** Conceptualization, S.H. ; data curation, S.H. ; formal analysis, S.H. ; methodology, S.H. ; funding acquisition, X.G. ; investigation, S.H. ; software, S.H. ; project administration, S.H. and X.G. ; resources, S.H. and X.G. ; supervision, S.H. ; validation, S.H. ; visualization, S.H. ; writing--original draft, S.H. ; writing--review and editing, S.H. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by National Natural Science Foundation of China (51778575). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The raw/processed data needed to reproduce these findings cannot be shared publicly at this time, as they are also part of ongoing study. **Conflicts of Interest:** The authors declare no conflicts of interest. **Nomenclature**