# Research on the Compactness of Lunar Soil Simulant Based on Static Cone Penetration Test
## 3 Results and Analysis
### Variation in Normalized Cone Tip Resistance with Penetration Depth  
The overlying pressure on the lunar soil simulant varies at different depths, which has a certain impact on the experimental results. Therefore, cone tip resistance is normalized to eliminate the influence of the overlying pressure and more accurately analyze the variation in cone tip resistance with penetration depth. [PERSON] et al. (2012) proposed the following normalization formula for the cone tip resistance and penetration depth:  
\[Q=\frac{q_{c}-\sigma_{v}}{\sigma_{v}^{\prime}} \tag{3}\]  
\[\sigma_{v}=\gamma z \tag{4}\]  
where \(Q\) represents the normalized cone tip resistance; \(q_{c}\) denotes the cone tip resistance; \(\gamma\) is the unit weight of the lunar soil, varying according to the compactness; \(z\) is the penetration depth of the probe; \(\sigma_{v}\) is the total overlying stress of the lunar soil at this depth; and \(\sigma_{v}^{\prime}\) is the effective stress. In this study, the water content of the lunar soil simulant is less than 1%, allowing the assumption that \(\sigma_{v}=\sigma_{v}^{\prime}\).  
The curves of the normalized cone tip resistance with the penetration depth after normalization are shown in Figure 6. For the lunar soil simulant with an overall compactness of 58%, the normalized cone tip resistance first increases, then decreases, and then increases again as the penetration depth increases, showing an overall growth trend. For the other three groups, the normalized cone tip resistance first increases and then decreases as the penetration depth increases.  
Figure 5: The variation curves of the cone tip resistance with the penetration depth under different overall compactness.  
As the overall compactness increases, the growth rate of the normalized cone tip resistance of the lunar soil simulant with the penetration depth also gradually increases. The normalized cone tip resistances of the four groups of the lunar soil simulant reach their maximum values at penetration depths of 60 cm, 58 cm, 56 cm, and 55 cm, in sequence. The penetration depth at which the normalized cone tip resistance of the lunar soil simulant reaches its maximum value becomes shallower as the overall compactness increases. Before the normalized cone tip resistances of the four groups of lunar soil simulant reach their maximum values, the value of the normalized cone tip resistance increases with compactness at the same penetration depth.  
The maximum values of the cone tip resistance and the normalized cone tip resistance for the lunar soil simulant with different compactness levels are shown in Table 4. As the overall compactness increases, the maximum value of both the cone tip resistance and the normalized cone tip resistance gradually increases. By comparing the curves of cone tip resistance and normalized cone tip resistance under the same compactness condition (overall compactness levels of 68%, 78%, and 86%), it is found that the cone tip resistance reaches its maximum value when the penetration depth is 60 cm, but it is impossible to determine its change trend at depths greater than 60 cm. However, the curve of normalized cone tip resistance with penetration depth shows a clear peak at depths of less than 60 cm. Therefore, this peak value can be used as the characteristic value of the normalized cone tip resistance for this compactness.