# Research on the Compactness of Lunar Soil Simulant Based on Static Cone Penetration Test
## 5 Conclusions  
In this study, the variation curve of the compactness of the lunar soil simulant with depth was obtained through layered measurements. Static cone penetration tests were carried out on the lunar soil simulant under different overall compactness levels, and models of the relationship between the cone tip resistance, the normalized cone tip resistance, and the compactness were obtained. A formula for establishing the relationship between compactness and normalized cone tip resistance was established, making it possible to predict the variation in the compactness at different penetration depths. The main conclusions are as follows:  
(1) The uniformity of the lunar soil simulant samples is affected by their overall compactness. The higher the overall compactness, the more uniform the simulant becomes. The difference in compactness between the top and bottom layers of the sample is smaller at higher compactness levels. The lunar soil simulant samples with lower overall compactness exhibit poorer uniformity.  
(2) The cone tip resistance of lunar soil simulants increases with an increase in the penetration depth, and eventually reaches a stable state under different compactness levels. The normalized penetration resistance first increases and then decreases as the penetration depth increases. Each overall compactness level of the lunar soil simulant has a specific, stable value and a specific peak value of the normalized cone tip resistance.  
(3) The compactness of lunar soil simulants increases with the increase in the normalized cone tip resistance. The correlation coefficient obtained between compactness and normalized cone tip resistance in functional model was 0.989. Thus, the compactness of real lunar soil can be predicted using this functional model. The relationship between compactness and the normalized cone tip of real lunar soil can provide strong support for relevant research and practices in in situ lunar surface testing.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Types of Lunar Soil Simulants** & **CUG-1A** & **CUMT-1** & **LSS** & **JSC-1** & **GRC-1** \\ \hline Median Particle Size/\(\upmu\)m & 70 & \textasci{-}100 & 105 & 119.7 & \textasci{-}260 \\ \hline \end{tabular}
\end{table}
Table 7: The median particle sizes of different types of lunar soil simulant [6; 27; 28; 29].  
(4) The cone tip resistance of the lunar soil continues to increase with the increase in penetration depth. Large-sized static cone penetration probes receive greater cone tip resistance, while small-sized probes are more likely to penetrate into highly dense lunar soil and are more suitable for use in the lunar surface environment. Therefore, future research directions include static penetration tests and mechanism studies of small-sized probes, static penetration tests of different types of lunar soil, and research on the prediction of the physical and mechanical parameters of lunar soil.  
Conceptualization, L.D. and X.F.; data curation, Y.Z. and S.X.; formal analysis, Y.Z. and S.X.; funding acquisition, H.G. and L.X.; investigation, H.G. and X.F.; methodology, H.G. and L.X.; supervision, H.G., X.F. and L.D.; writing--original draft, Y.Z.; writing--review and editing, H.G., X.F., S.X., L.X. and L.D. All authors have read and agreed to the published version of the manuscript.  
Financial support was received from the Nation Key R & D Program of China (2023 YFB3711300).  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
The authors declare no conflicts of interest.