# Study on Compaction Characteristics and Compaction Process of an Unsaturated Silt Based on PFC3D
## 4 Research on the Rolling Compaction Process
### Analysis of the Compaction Results  
#### 4.3.1 Relationship between the Compaction Effect and Rolling Times  
Figure 10 shows the relationship between the number of static rolling and the degree of compaction. It can be seen that the whole rolling process can be divided into two stages. The first stage is the initial rolling stage. Under the rolling action of the roller, the friction force and the liquid bridge force are overcome between the particles, the large and small particles are filled with each other, the porosity decreases rapidly, and the compaction degree of the model is improved obviously, such as during the first and second rolling. The second stage is the re-grinding stage. When the rolling model is compacted to a certain extent, the porosity is small, the particles are relatively stable, and it is not easy to move and fill. Under the rolling effect of the roller, the compaction degree of the sample is further reduced, but the compaction degree does not change significantly. When analyzing the contact force chain between particles, it is necessary to set up a shear plane to analyze the contact force chain inside the model. Figure 11a-e shows the distribution of the particle contact force chain under different rolling times. Table 4 shows the numerical change in the contact force chain between the particles. Figure 10: Relationship curve between the compaction degree and rolling times. \begin{table}
\begin{tabular}{c c c c} \hline
**Grinding Wheel Weight/N** & **Exciting Force/N** & **Vibration Frequency/Hz** & **The Gait of March/m\({}^{*}\)-s\({}^{-1}\)** \\ \hline
505 & 928 & 30 & 0.1 \\ \hline \end{tabular}
\end{table} 
Table 3: Roller discrete element simulation parameter table. From Figure 11 and Table 4, it can be seen that before the rolling operation, the distribution of the contact force chain between the particles is relatively uniform, and the value of the contact force chain is maintained at 2.52 \(\times\) 10\({}^{5}\) N. With the continuous rolling, the contact force chain between the particles gradually tends to be dense, from the blue with a lower value, to the red with a higher value, and the closer to the bottom of the model, the denser the contact force chain is. After the second rolling, the growth amplitude of the contact force chain gradually decreases, from 0.39 \(\times\) 10\({}^{5}\) N in the third rolling, to 0.09 \(\times\) 10\({}^{5}\) N in the seventh rolling. Considering the changes in the compaction degree and contact force chain, after five times of rolling, the compaction degree of the compacted soil and the thickness of the rolling layer change with the increase in rolling times, but the overall change amplitude is very small, and the contact force chain between the particles is also in a relatively stable state. If the rolling is continued on this basis, the saturation of the soil sample will likely increase due to excessive rolling, which will promote the development of the soil sample from dry to wet, and reduce its bearing strength. Therefore, the reasonable rolling amount obtained by discrete element simulation is five times. \begin{table}
\begin{tabular}{c c} \hline \hline
**Rolling Times** & **Contact Force Chain Size/N** \\ \hline
0 & 2.52 \(\times\) 10\({}^{5}\) \\
1 & 6.84 \(\times\) 10\({}^{5}\) \\
2 & 1.06 \(\times\) 10\({}^{6}\) \\
3 & 1.35 \(\times\) 10\({}^{6}\) \\
4 & 1.74 \(\times\) 10\({}^{6}\) \\
5 & 1.98 \(\times\) 10\({}^{6}\) \\
6 & 2.14 \(\times\) 10\({}^{6}\) \\
7 & 2.23 \(\times\) 10\({}^{6}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Table of the contact force chain changes under different rolling times. Figure 11: Distribution diagram of the contact force chain under different rolling times. (**a**) Not rolled. (**b**) Rolled once. (**c**) Rolled three times. (**d**) Rolled five times. (**e**) Rolled seven times. 4.3.2.