## 2 Materials and Methods  
Field observations, in situ experiments, and laboratory tests were conducted to determine the geotechnical parameters necessary for designing the soil nail support system in the sandstones of the Cakraz Formation. Various images of the study area at different stages are shown in Figure 3.  
Figure 3: Various images of the study area at different stages: (**a**) boring; (**b**) pressure meter; (**c**) pull-out test equipment on a soil nail; (**d**) data logger for strain gauge reading; (**e**) pull-out test readings. Figure 2: A schematic related to the principles and building of the model. Three boreholes were drilled at different depths to obtain geological, engineering geological, and geotechnical data. The boreholes (BH-23: 35.0 m, BH-24: 30.0 m, and BH-19: 20.0 m) were located near the soil-nailed support structure (Figure 4). The weathered rock mass was classified according to the six-grade weathering system suggested by the ISRM [21] (Table 1). In order to determine the mechanical properties of the studied weathered rock based on the profile given above, a standard penetration test (SPT) was conducted on the top of the landform, particularly in residual and completely weathered sections. Additionally, pressure meter tests were also carried out in all the existing boreholes to obtain the deformation parameters of the rock and soil masses. Unconfined compressive strength tests and triaxial compression tests were conducted to determine the mechanical properties of the soil layers. Additionally, the uniaxial compressive strength of the rock was determined using uniaxial compression tests, and point load tests were performed when UCS samples were unavailable. Physical properties (e.g., unit weights and porosities) were also evaluated for both rock and soil sequences in accordance with the ISRM [22] and ASTM [23] guidelines. Numerical models were generated via the finite element method using the obtained geotechnical parameters. Horizontal displacement values and safety coefficients were identified through finite element analysis using the Mohr-Coulomb constitutive model. \begin{table}
\begin{tabular}{c c c} \hline
**Weathering** & **Degree of Weathering** & **Typical Features (kN/m3)** \\ \hline Residual Soil & W6 & All rock material is converted into soil. The mass structure and material fabric are destroyed. There is a large change in volume, but the soil has not been significantly transposed \\ Completely Weathered & W5 & All rock material is decomposed and/or disintegrated into soil. The original mass structure is still largely intact \\ Highly Weathered & W4 & M
\begin{tabular}{c} More than half of the rock material is decomposed or has \\ disintegrated into soil. Fresh or discolored rock is present either \\ as a continuous framework or as core stone \\ Less than half of the rock material is decomposed or has \\ disintegrated into soil. Fresh or discolored rock is present either \\ as a discontinuous framework or as core stones \\ Disoloration indicates weathering of rock material and \\ discontinuity surfaces. All rock material may be discolored \\ by weathering \\ Fresh Rock & W1 & No visible signs of rock material weathering. There is perhaps \\ slight discoloration on the major discontinuity surface \\ \hline \end{tabular}
\end{table} 
Table 1: Weathering grades and typical properties of rocks [21]. Figure 4: Map showing the locations of boreholes (the blue boundary with a dashed area indicates the project area). The performance of the soil-nailed wall system was assessed based on numerical analysis results, inclinometer measurements, and soil nail pull-out tests in which strain gauge sensors were employed. Nail behavior and the load transfer mechanism from nail to soil were evaluated using strain gauge sensors placed on the nails subjected to pull-out tests. During soil nail pull-out tests, only the displacement at the tip of the soil nail can be measured under tensile load.