## 4 Discussion  
Integrating InSAR, GPR, and ERT methodologies provided a comprehensive framework for assessing subsidence along Road 431. Validation by borehole drilling further solidified the interpretations derived from these geophysical methods, ensuring accuracy in delineating subsurface features. InSAR Results: The PSI analysis successfully captured surface subsidence's spatial and temporal patterns. Point C exhibited the highest subsidence rate of \(-2.7\) cm/year, indicative of significant localized instability, likely due to voids, soil compaction deficiencies, or altered groundwater conditions. In contrast, Point D, with a minimal subsidence rate of \(-0.6\) cm/year, served as a stable reference, highlighting the spatial variability in ground subsidence. These observations align with borehole drilling data, which confirmed the presence of karstic voids at depths of 45-49 m and severely weathered chalk layers below 49 m, correlating with the low-resistivity anomalies identified in ERT corresponding to the identified subsidence hotspots. However, the InSAR analysis was hindered by decorrelation in high-noise areas, caused by nearby construction and vehicular movement. Despite these challenges, the method's high precision in monitoring surface subsidence proved invaluable as an early warning system for ground instability. GPR Insights: The analysis identified critical subsurface anomalies, including fragmented fill layers and voids within the subsidence zone. Radargrams showed evident depressions (concavities) in the asphalt and granular layers, indicating structural breakdown likely caused by water infiltration and the displacement of fine particles. Stable zones displayed linear stratification, confirming the absence of subsidence. The GPR findings were corroborated by borehole data, indicating air-filled voids and disintegrated fill layers within the affected areas. While GPR's penetration depth was limited in certain soil types, its ability to detect fine-scale variations was instrumental in diagnosing the underlying mechanisms of subsidence. ERT Contributions: ERT complemented the GPR findings by providing a broader perspective on subsurface resistivity distributions. The detection of low-resistivity anomalies at depths of 50-100 m aligned with the voids and disrupted layers identified in the borehole logs. Additionally, delineating groundwater pockets further substantiated the influence of hydrological processes on subsidence. ERT's capacity to penetrate deeper subsurface layers enhanced the understanding of subsidence patterns. The integration of resistivity anomalies with the structural features observed in the GPR and InSAR data highlighted the interplay of geological and hydrological factors driving ground instability. Integration and Validation: The combined application of InSAR, GPR, and ERT demonstrated the success of an integrated geophysical approach in addressing subsidence challenges. Each method offered unique strengths: InSAR excelled in surface subsidence monitoring, GPR provided detailed subsurface imagery, and ERT extended the depth of investigation. Borehole drilling validated the geophysical findings, confirming the presence of voids, cavities, and groundwater-related subsurface heterogeneity. The integration of these methods allowed for a nuanced understanding of subsidence mechanisms, emphasizing the role of water movement, soil erosion, and compaction deficiencies. This synergy underscores the importance of multi-method frameworks in tackling complex geotechnical issues. Implications and Future Directions: While the findings offer robust insights, challenges remain, particularly in mitigating noise interference and interpreting complex resistivity anomalies. Future studies should incorporate real-time monitoring systems and expand borehole investigations to refine subsidence predictions and inform remediation strategies.