# Study on Compaction Characteristics and Compaction Process of an Unsaturated Silt Based on PFC3D
## 5 Conclusions  
In this paper, the discrete element software, PFC3D, is used to simulate and analyze the static triaxial test, and the rolling compaction process simulation and engineering field measurement are carried out to obtain the best rolling compaction process of soil samples under the best water content. The following conclusions are drawn:  
1. This article relates matrix suction to water content and uses matrix suction to approximate the water content state of soil samples. By comparing the results of the discrete element simulation triaxial compression test with the indoor triaxial compression test, the microscopic parameters of the unsaturated soil model were calibrated, and the accuracy of using matrix suction to characterize the water content state was verified. The feasibility of using Hill contact simulation of unsaturated soil was also confirmed. 2. During the simulation of the rolling process using the PFC3D software, it was found that the relationship between the number of static rolling and the degree of compaction is proportional. The change in compaction degree in the whole rolling process can be divided into two stages: the first stage is the initial rolling stage, and the compaction degree of the model increases rapidly in this stage. The second stage is the re-grinding stage. The particles are relatively stable, and the increase in compaction degree is not significant. The reasonable rolling times are preliminarily determined to be five times, according to discrete element simulation. 3. Through PFC3D software simulation, the changes in compaction degree under different rolling process combinations under the optimal moisture content conditions were analyzed. The results showed that compared with static compaction, both strong and weak vibration compaction can significantly improve the compaction effect of the roadbed compaction model. The larger the amplitude of the roller vibration, the \begin{table}
\begin{tabular}{c c} \hline
**Compaction Combination** & **Degree of Compression** \\ \hline Static rolling 1 time + Weak vibration 2 times & 90.8\% \\ Static rolling 1 time + Weak vibration 3 times & 92.2\% \\ Static rolling 1 time + Weak vibration 4 times & 94.6\% \\ Static rolling 1 time + Weak vibration 5 times & 95.3\% \\ Static rolling 1 time + Strong vibration 3 times & 93.2\% \\ Static rolling 1 time + Strong vibration 4 times & 96.4\% \\ Static rolling 1 time + Strong vibration 5 times & 94.3\% \\ Static rolling 1 time + Weak vibration 2 times + Strong vibration 2 times & 96.6\% \\ Static rolling 1 time + Strong vibration 2 times + Weak vibration 2 times & 98.1\% \\ \hline \end{tabular}
\end{table} 
Table 5: Variation of the compaction degree for different compaction combinations at 15% moisture content. more obvious the improvement of this compaction effect. For the combination of strong vibration and weak vibration compaction, the compaction effect of strong vibration followed by weak vibration is stronger than that of weak vibration followed by strong vibration. 4. Taking the unsaturated silt roadbed of the Dezhou-Qihe section of the Jingtai Expressway as the research object, the rolling test of a cement-modified unsaturated silt roadbed under the optimum moisture content was carried out using a field test to determine the optimum rolling compaction combination under this moisture content. According to the field test data, it can be seen that when the water content is 15%, the best compaction combination is static rolling once + strong vibration twice + weak vibration twice, which is consistent with the discrete element simulation results and has a certain guiding role in the construction of the project site. Conceptualization, Z.M. ; Methodology, Z.M. and K.L. ; Software, K.L. and D.S. ; Validation, D.S. ; Formal analysis, W.L., Y.W. and S.L. ; Investigation, W.L. ; Data curation, Y.W. and S.L. ; Writing--original draft, K.L. ; Writing--review & editing, K.L. ; Visualization, D.S. ; Supervision, Z.M. ; Project administration, Z.M. ; Funding acquisition, Z.M.