## 3 Results and Discussion
### Performance of the Soil Nail System
#### 3.2.2 Soil Nail Pull-Out Tests Employing Strain Gauge Sensors  
The soil nail pull-out test is another method used to evaluate system performance. This test determines the interaction between the soil and nail via measuring bond strength. Figure 14 shows a picture of the soil nail pull-out test being applied. The ultimate bond strength is influenced by shear stresses along the soil-grout interface, which depend on tensile force application, injection properties, and geological conditions. The mobilized unit length is defined using the tensile value Q [3]. \[\text{Q}=\pi\text{qD}_{\text{DH}}, \tag{1}\]  
Figure 13: Inclinometer results. \begin{table}
\begin{tabular}{c c c} \hline \hline \(\mathbf{u_{x}}\) & **Section 1–1’** & **Section 2–2’** \\ \hline Preliminary Design & 2.22 & 1.53 \\ \hline Field Measurement & 0.23 & 0.39 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Comparison of preliminary-design horizontal displacement versus field measurements. where q is shear strength mobilized at the grout-soil interaction surface, and D\({}_{\text{DH}}\) is effective drilling hole diameter. The relationship between tensile force and the shear stress at the interface is expressed as follows:  
\[\text{dT}=\pi\text{D}_{\text{DH}}\text{q}\text{dx}=\text{Q}\text{dx} \tag{2}\]  
At any reinforcement distance (x), the tensile force (T) equates to the following:  
\[\text{T}(\text{x})=\int_{0}^{\text{x}}\pi\text{D}_{\text{DH}}\text{q}\text{dx} =\int_{0}^{\text{x}}\text{Q}\text{dx} \tag{3}\]  
At the point where the length of the soil nail reinforcement root (Lp) is subjected to tension ends, the nail force is as follows:  
\[\text{T}(\text{L}_{\text{P}})=\text{T}_{0}=\text{Q}\text{L}_{\text{P}} \tag{4}\]  
The nail pull-out capacity (T\({}_{\text{max}}\)) is expressed as follows:  
\[\text{R}_{\text{P}}=\text{T}_{\text{max}}=\text{Q}_{\text{u}}\text{L}_{\text{P} }=\pi\text{q}_{\text{lult}}\text{D}_{\text{DH}}\text{L}_{\text{P}} \tag{5}\]  
where Q\({}_{\text{u}}\) is the tensile capacity per unit length (pull-out resistance per length), and q\({}_{\text{lult}}\) is the ultimate bond strength. Within the scope of the in situ test, two soil nail pull-out tests were conducted. The first of the pull-out tests (PT1) was carried out on a completely weathered sandstone unit, and the second (PT2) was conducted on a moderately weathered sandstone unit. In PT1, 28 mm ribbed reinforcement was used, and a 40 mm diameter ribbed reinforcement was used to increase the cross-sectional area. Both tests had a free length of L = 2.00 m and a root length of L = 4.00 m, with a drill diameter of 127 mm. In the experiments, strain gauge sensors and comparator clocks were used to measure the amounts of displacement and extension. The strain gauges were placed at certain points on the ribbed rebars in the experimental setup (Figure 15). Each strain gauge sensor was secured to soil nail reinforcement using a stabilizer guide and welded to ribbed reinforcement from both ears, allowing for free movement within the sensor (Figure 16). The loading program recommended by the FHWA [33] was used to determine which soil nail pull-out test procedure to use (Table 6). The design loads (DLs) in the pull-out tests were determined using bond strengths obtained from the literature. In experiments PT1 and PT2, the DL values were determined to be 120 kN and 320 kN, respectively. Figure 14: Setup of the soil nail pull-out test. GeoSense [34] was used to explain the values measured via the strain gauges used within the scope of this study and convert the raw data. Micro-stress change (\(\Delta\mu\epsilon\)) could be calculated using frequency unit (Hz) and linear digit (B) values obtained from a handheld computer (a data logger) using Equation (6).