# Research on the Compactness of Lunar Soil Simulant Based on Static Cone Penetration Test
## 4 Discussion  
For actual lunar exploration, it is necessary to predict the compactness of lunar soil at certain depths based on the results of static cone penetration tests. Therefore, converting the curve of the normalized cone tip resistance varying with compactness in the above research into a curve of the compactness varying with the normalized cone tip resistance is more in line with the actual needs of lunar exploration. The normalized cone tip resistance at 58%, 68%, 78%, and 86% compactness was calculated using Equations (7) and (8) to be 93.7, 209.6, 487.1, and 1338.5. The purpose of this article was to predict the compactness of lunar soil simulant based on its normalized \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Data Processing** & **58\%** & **68\%** & **78\%** & **86\%** & **Fitting of All Points** \\ \hline Before Normalization & 0.97 & 0.99 & 0.98 & 0.97 & 0.95 \\ After Normalization & 0.95 & 0.99 & 0.90 & 0.97 & 0.97 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The correlation coefficient of the fitted curve corresponding to the cone tip resistance of the lunar soil simulant with compactness. cone tip resistance. Therefore, four calculated values were used to fit a new curve showing the variation in compactness with normalized cone tip resistance. The curve equation is  
\[D=10.59\ln(Q)+10.86,R^{2}=0.989 \tag{9}\]  
According to the mineral composition classification of the lunar soil, CUG-1A is a typical low-titanium basaltic lunar soil simulant. Among the numerous lunar soil simulants, CUMT-1 developed by China University of Mining and Technology [23], GRC-1 developed by the U.S. Army Engineer Waterways Experiment Station [24], the LSS-type developed by NASA's Glenn Research Center [25], and JSC-1 developed by NASA [26] are all typical low-titanium basaltic lunar soil simulants. Figure 9 shows the variation curves of the compactness with the normalized cone tip resistance of different types of lunar soil simulants. Among them, the cone tip angle of the static cone penetration test probe for the LSS lunar soil simulant is 30\({}^{\circ}\), while those for the remaining lunar soil simulants are all 60\({}^{\circ}\). It can be seen from the figure that the compactness of different lunar soil simulant is positively correlated with the normalized cone tip resistance. When the normalized cone tip resistance increases from 93.7 to 1338.5, the compactness of the CUG-1A lunar soil simulant increases from 58% to 86%. Observing the fitting curves and their varying trends for CUG-1A, JSC-1, and GRC-1, it can be concluded that the compactness of all three lunar soil simulants is around 80% at a normalized cone tip resistance of around 750. When the normalized cone tip resistance is less than 750, the compactness is at a low to medium level. At this point, the compactness of CUG-1A is higher than that of JSC-1 and GRC-1. When the normalized cone tip resistance is greater than 750, the compactness of CUG-1A is medium to high. Here, the compactness of CUG-1A is lower than that of JSC-1 and GRC-1. As the normalized cone tip resistance increases, the compactness of the CUG-1A lunar soil simulant also gradually increases, showing a relatively low sensitivity to the normalized cone tip resistance, and eventually becomes lower than that of the majority of the remaining lunar soil simulants shown in the figure. Figure 9: The variation curves of the compactness of different lunar soil simulants with the normalized cone tip resistance [6; 27; 28; 29]. Since there are several types of low-titanium basaltic lunar soil simulants with little difference in their mineral composition, it can be stated that the differences in the normalized cone tip resistance are not caused by mineral composition. By comparing the variation in the compactness curve of different lunar soil simulants, the LSS simulant has the lowest normalized cone tip resistance due to the small cone tip angle of the probe.