Modeling subsurface instabilities for urban infrastructure resilience via novel joint microgravity and geotechnical methods

In urban areas with complex geological formations, such as Petaling Jaya in western Peninsular Malaysia, assessing subsurface conditions is crucial for the safe and efficient design of infrastructure foundations. Traditional methods often fail to address the variability and heterogeneity of soil-rock profiles, which are key to predicting load-bearing capacity and preventing structural failures. This study introduces a novel microgravity-geotechnical approach, integrating Bouguer and residual with enhanced gravity-derivative and gravity anomaly depth-structure modeling as well as borehole data (SPT-N and RQD) to examine subsurface features and structural instabilities. The gravity models highlight significant low-density anomalies corresponding to weathered silty sands, sandy silts, and fractured limestone, while derivative and tilt angle maps reveal curvilinear structures, suggesting tectonic or karstic dissolution processes. These features, along with observed weak zones, exacerbate the risk of uneven settlement, subsidence, and structural damage, which are already evident in the area's infrastructure. Borehole and depth-structure gravity models confirm variability in subsurface materials, with competent layers extending between 18 and 85 m in depth, underscoring the importance of precise foundation siting. Areas with low-density or fractured materials are evidently unsuitable for shallow foundations and require reinforcement, including deep foundation anchoring and specialized piling. The findings of this research provide critical insights for infrastructure design in regions with complex geological features, offering guidance on reliable siting and remediation of failing infrastructure. The approach established in this study can be applied to other terrains facing similar subsurface challenges, promoting safer and more resilient infrastructure development.