## 5 Results and Discussion
### CSNS Site  
The rocks exposed at the surface of the 400 mu (266,800 m\({}^{2}\)) site, known as the SIA (Site Installation Area), are mainly composed of unconsolidated Quaternary sediments, Cretaceous granite, and Sinian gneiss. The potential geotechnical issues for this RI consist of slope instability and uneven foundation settlement. After dividing the 400 mu area (the SIA) of the CSNS site into 12,086 sub-units, we calculated the _EGSI_ value for each sub-unit. Using the standard mining method, we used the _EGSI_ value and the size of each sub-unit to divide the SIA into engineering geological suitability zones per the natural breaks (Jenks) method in ArcGIS [50]. An example of this approach for the CSNS site is shown in Figure 4, guided by the _EGSI_ index. We used the ArcGIS software to quantify the factors that might affect the area's stability and suitability, such as potential geohazards (mainly landslides), suitability zonation, basement stability, standard penetration, weathering thicknesses, unconsolidated Quaternary sediment layer thicknesses, rock lithologies, and slope gradation (Figure 4). ArcGIS is a registered trademark of ESRI (Environmental Systems Research Institute) (ArcGIS (TM) [51]). This zoning map incorporates various influencing factors of the potential RI site; these factors provide actionable advice for designing and constructing the RI. As shown in Figure 4, the engineering geological suitability of the south-central and southeastern parts of the SIA is better than it is for the northern part of this study area. Based on this information, we see that the northern half of the SIA is more unstable than the southern half because of the presence of thick, highly weathered and/or unconsolidated Quaternary sediment layers that are highly fractured or have low mechanical strength. The southern half of the SIA resides on exposed bedrock and is more stable from a geoengineering perspective. However, the combination of steeper slopes and the soft, fractured rocks located near the line accelerator indicates that this part of the RI could be threatened by the instability of the high-cut slope (Figure 4b). Taken together, the stability of the foundation and the disaster susceptibility of the installation area determine the engineering geological suitability. Based on these data, we recommended that the CSNS ring accelerator and the target zone device (middle position in Figure 4a) should be placed in south-central and southeastern parts of the site, rather than the northern part of the SIA. This recommendation was implemented during the construction of this part of the RI [34]. The CSNS borehole weathering shells are shown in Figure 5a. In the southern part of the site, the thickness of the weathered crust is small, extending to a depth of ~10 m. In the auxiliary area, which is located in alluvial soil, the Quaternary unconsolidated sediment layer and completely weathered granite layers are thicker and are visible throughout the entire borehole. The rock core index (_RCI_) increases with depth (Figure 5b) and generally corresponds to the different weathering zones. The _RCI_ of the underground cores throughout the entire CSNS site ranges from 0 to 30, and the _RCI_ value of the borehole that samples fracture zone in the main device area is 10. The _RCI_ of the Quaternary alluvial and completely weathered granites is about 0, while the _RCI_ of the strongly weathered granite, slightly weathered granite, and fresh granite are 0-3, 8, and 13, respectively. The _RCI_ values of the rock layer are generally less than 30 at depths less than 100 m.  
The _RCI_ results for the linear accelerator section of the site show distinct variations with depth and fracturing degree (Figure 4c). The two red regions highlighted in Figure 4c represent moderately weathered and slightly weathered granite with low _RCI_ values; these zones are consistent with the actual fracture distribution in the area, as revealed by drilling (such as borehole ZZZK94).