## 1 Introduction  
Soil nails are rigid reinforcement elements placed on specific slopes to provide temporary or permanent stability in soils or weathered rock environments [1]. These reinforcement elements are placed within the borehole after the drilling is completed. Following the installation of a soil nail, a cement grout mixture is injected to ensure good resistance to adherence stress (bond strength) via load transfer between the cement-grouted soil nail and the soil/weathered rock.  
In situ observations and field practices emphasize the importance of evaluating the support system's performance after soil nail installation and grouting.  
Retaining wall monitoring is a widely used method of ensuring long-term stability. Inclinometer measurements are particularly useful for assessing retaining wall deformations, and many researchers have applied this method to soil-nailed support systems [2; 3]. Furthermore, in situ soil nail pull-out tests also provide reliable data on nail performance and soil nail adhesion stress during the construction of soil-nailed walls [4; 5; 6; 7; 8; 9; 10; 11; 12; 13]. It is well known that some environmental effects may change the behavior of a soil nail. The roots of plants basically have a positive effect on soil strength. Vegetation reduces runoff water on the surface of the soil. However, if the vegetation layer on the soil's surface is damaged, then the soil will be exposed to meteorological conditions and weathering effects, which can easily decrease shear strength and cause slope erosion [14; 15]. The engineering geological properties of weathered residual soil also change with time [16]. Nail force is affected by time and excavation [17]. This leads to an increase in nail force. As the shear strength of the soil decreases, there is an increase in the displacement and interaction between the soil and nails. During the excavation phases, nail forces tend to increase. Groundwater also has an adverse effect on fully grouted rock bolts during the pull-out test: the pull-out strength is lower than under dry conditions [18]. Fluctuations in groundwater levels and weathering effects, especially on the roots of soil nails, decrease the shear strength between soil nails and the soil in the long term. Therefore, groundwater penetration should be prevented or limited in soil-nailed sections. Also, slopes should be protected against weathering agents (e.g., water infiltration). Despite the ISRM's requirements, the height-to-width ratio is lowered by the water-sensitive nature of shale rock [19]. Furthermore, water infiltration increases the deformation of weathered rocks [20].  
In this study, we examined a 200.0 m long soil-nailed retaining wall with a height varying between 8.00 m and 10.0 m constructed in the Tasksi@ region of Sakarya province (Turkiye) within the Cakraz Formation (Figure 1).  
Figure 1: Location maps of the study area.  
Inclinometers were placed behind the retaining wall to monitor horizontal deformation, and soil nail pull-out tests were conducted to determine adhesion stress values. The second phase involved numerical analysis using the Mohr-Coulomb constitutive model, incorporating site-specific engineering geological properties and geotechnical data used in the design. The study continued with a comparison of the deformation data obtained from in situ measurements and numerical analyses. In order to investigate discrepancies in deformation, the engineering geological and geotechnical parameters of the slope were used in sensitivity and parameter analysis. All these parameters were then re-analyzed using the Hoek-Brown constitutive model (Figure 2).