# Experimental Study on Shear Creep Characteristics of Residual Soil with Different Stone Content
## 7 Discussion  
The deformation and strength of the residual soil are closely related to its soil and stone structural characteristics, which can be observed through macroscopic particle displacement and fragmentation. The role of coarse particles in providing a skeleton framework and the embedding role of fine particles undergo significant changes with varying stone content  
Figure 11: Stress–strain isochronous curve point of 50% stone content specimen.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Consolidation Pressure/kPa** & **Stone Content\%** & **Instantaneous Strength/kPa** & **Long-Term Strength/kPa** & **Reduced Factor** \\ \hline \multirow{4}{*}{200} & 10 & 140 & 69.5 & 0.49 \\  & 30 & 161.5 & 82 & 0.53 \\ \cline{1-1}  & 50 & 184 & 104 & 0.57 \\ \cline{1-1}  & 70 & 198 & 112 & 0.57 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Long-term strength of the sample.  
in residual soil. Consequently, the transient shear strength and long-term strength of the soil are also affected. To analyze the impact of particle gradation on residual soil strength, the uniformity coefficient and curvature coefficient of the coarse-grained soil are employed. It is determined that when the uniformity coefficient (Cu) exceeds 5, and the curvature coefficient (Cc) falls within the range of 1-3, the soil sample exhibits well-graded properties. In cases where the gradation is satisfactory, a higher uniformity coefficient implies a more pronounced compaction effect and a more evenly distributed and rational force transmission. Figure 12 displays the uniformity coefficient and curvature coefficient of samples with different stone contents. It is evident that, although the uniformity coefficient of each stone content specimen exceeds 5, the curvature coefficient of specimens with 10% and 30% stone content is equal to or less than 1. This indicates an excessive presence of fine particles in these specimens, which hinders the formation of a well-compacted skeleton structure.  
The grading condition of residual soil directly affects its strength characteristics. As the stone content increases, the instantaneous shear strength shows a linear increase, while the long-term strength exhibits a smaller value below 50% stone content and a larger value above 50% (refer to Figure 13). This phenomenon can be attributed to the following factors: in the instantaneous shear test, equal strain loading was applied, resulting in a higher proportion of large boulders on the shear surface. This leads to greater resistance during shear, increased fragmentation of large particles, and, consequently, higher shear strength. During the creep test, step-by-step equal stress loading was employed. In specimens with a stone content below 10% and 30%, the higher concentration of fine material leads to a loose soil structure, resulting in a significant decrease in long-term strength. On the other hand, specimens with a stone content of 50% and above exhibit good gradation and a dense structure, leading to a noticeable increase in long-term strength.  
Figure 12: Uniformity coefficient and curvature coefficient with different stone content.  
Overall, the long-term strength of residual soil is more influenced by gradation effects than its instantaneous shear strength. In future studies, advanced analysis methods such as fractal theory can be utilized to analyze the influence of residual soil gradation on its long-term strength.  
Furthermore, studies have indicated that the long-term strength and instantaneous shear strength of 70% of the samples exhibit only marginal improvements compared to 50% of the samples, with insignificant growth. Existing research has found that, with an increase in stone content, the cohesion of the sample initially increases. However, beyond a certain stone content value (some suggest around 60%), the cohesion starts to decrease [29]. At higher levels of stone content, such as 80, the soil may become non-cohesive, resulting in a reduced shear strength [30].