## 5 Conclusions  
The compaction characteristics and California Bearing Ratio of weakly expansive soil were studied. The pore size distributions of samples with different compaction degrees were determined by NMR; at the same time, the effect of freeze-thaw cycles on the pore size distribution and CBR value was studied.  
1. Based on compaction tests conducted on Jiamusi weakly expansive soil with different moisture contents and compaction energies, it was found that the moisture content corresponding to the maximum CBR value was greater than the optimal moisture content. At the same degree of compaction, the CBR values of the samples with moisture contents above and at the optimum were higher than the CBRs of the samples with lower moisture content. According to whether the moisture content was less than, equal to, or greater than the optimal, three different straight lines could be fitted to describe the change in CBR with compaction. As the number of freeze-thaw cycles increase, the CBR value decreases slightly. After 12 freeze-thaw cycles, the CBR values of the samples with 19% moisture contents and 90% compaction degree decreased by 16%, and the CBR values decreased by 10% for the samples under 100% compaction degree with 16.4% moisture contents.
2. The mechanism affecting the CBR was analyzed at the macroscale and microscale. From the macroscale perspective, the bearing strength of expansive soil is mainly affected by the expansion and dry density. If the moisture content is slightly greater than optimal, Jiamusi weakly expansive soil has a small expansion strain after immersion (less than 0.83%) and large CBR value. However, too much moisture makes the dry density too low, resulting in a small CBR value, even when the expansion is small. From the microscale perspective, soils with small expansions have more micropores according to the results obtained by NMR. After the freeze-thaw cycles, for the soil with K = 90% and w = 19%, the expansion increased by 65%and the CBR decreased by 10%; the expansion increased by 86% and CBR decreased by 16% for the soil with K = 100% and w = 16.4%. The freeze-thaw cycles decreased the CBR value, because they increased the pore volume. Soils with larger pore volumes experienced greater expansion after being soaked in water.
3. When subjected to freeze-thaw cycles, soils with different compaction degrees behave differently. When N\({}_{\text{FT}}\ <\ 4\), there was little change in the pore size distributions and void ratios of the dense soil. Until N\({}_{\text{FT}}\geq 4\), the pore structure of the soil varied significantly. Space was provided for the adjustment of the soil particles when the soil was loose, causing the pore size distribution to vary in the early freeze-thaw cycles, whereas the void ratio remained constant. For the dense sample, after 12 freeze-thaw cycles, the void ratio and pore size distribution still did not reach a stable state, while the pore size distribution reached a new equilibrium state for the loose sample after eight freeze-thaw cycles.
4. This study investigated the road performance of weakly expansive soil as an embankment filler under the most unfavorable conditions (e.g., water immersion and freeze-thaw cycles). As suggested from the results, it can sufficiently satisfy the requirements. Compared with the optimal moisture content, the content corresponding to the maximum CBR value can result in higher strength that is better maintained over 12 freeze-thaw cycles.  
The paper was written by [PERSON] under the guidance of [PERSON]. The formal analysis and pre-literature research were carried out by [PERSON] and [PERSON]. The laboratory tests were carried out by [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
This research were funded by the financial support of the National Key R&D Program of China (Grant No.2019 YFC1509901).  
The authors declare that they have no conflicts of interest.