## 3 Results
### ERT-Results  
The ERT survey was conducted to understand the location of underground voids beneath the road structure, probing depths down to 100 m below the road surface. The Wenner-Schlumberger array configuration was employed for the measurements, offering a balanced approach to resolution and penetration depth. The depression observed in the northern lane of the highway is prominently featured in the survey results, positioned centrally in the cross-section and marked with a yellow star in Figure 8, where four ERT measurement lines were strategically positioned across the study area to refine the analysis further. The specific configurations and locations of these lines were as follows:  
Figure 17: A spatial cross-section of the subsidence area across all lanes, illustrating a “winged” depression pattern. The asymmetry, with the western wing elevated above the eastern wing, indicates localized water trapping east of the tilt. Figure 18: The GPR findings are synthesized on a map, showing the subsidence area (blue), water channel (yellow), and core subsidence zone with air voids (white). Line 0211: Conducted along a dirt path north of the northern road, providing a perspective on subsurface conditions beyond the immediate roadway. Line 0208: Performed along the northern shoulder of the north road to assess lateral variations in the subsurface near the edge of the pavement. Line 0210: Positioned on the southern lane of the northern road, extending towards areas near sunset to capture resistivity changes directly beneath the road structure. Line 0209: Located on the southern shoulder of the northern road, extending near sunset, offering complementary data to Line 0210 for cross-verification of the findings. Figure 19 shows the inversion results for these four lines arranged geographically from west (Lod) to east (Modi'in). The analysis allows for distinguishing four groups of soils and rocks based on their resistivity diapason: very low, low, medium, and high. For instance, the \"very low\" resistivity category (up to 6 Ohm-m) includes clayey soils and soft rocks like marl and marly chalk. The second group comprises soil and rock, whose resistivity ranges between 6 and 20 Ohm-m. It typically comprises gravelly soil, eroded limestone, etc. The third group range is 20-100 Ohm-m, usually represented by micro grain stiff limestone and dolomite. The resistivity for the fourth group is more than 100 Ohm-m, known in the site under study as very stiff limestone with a low potential for karst creation. The data for four geoelectrical cross-sections were enhanced by applying scale stretching to emphasize interlayer changes and ensure consistent section normalization. Figure 19: The inversion results for four ERT lines. Observations derived from the geophysical cross-sections in Figure 19 include the following: A. Geological Stratification: the subsurface can be broadly divided into three main layers:  
1. Layer 1: Extends from 0 to 20 m depths and exhibits notable heterogeneity, with folds and synclines suggesting the pathways of ancient streambeds. These features may contain conglomerates or heterogeneous soils, such as alluvium with embedded pebbles or breccias. 2. Layer 2: Spans 20-40 m depths and shows more excellent continuity, particularly in the northernmost and southernmost sections. However, localized heterogeneity is evident along the northern road, particularly around the 340 m mark. 3. Layer 3: Located at depths between 40 and 100 m. This layer shows \"topographic\" undulations, with its depth decreasing from the northern section by approximately 10 m near the southernmost measurement line, reflecting an overall slope in the subsurface layers. B. Discontinuity in Layers: The east-west orientation reveals interruptions in all three layers. These discontinuities likely reflect varying rock qualities within the same geological stratum.