Hydro-Mechanical Coupling Analysis of Field Pumping Test in Granite Residual Soil Site

In addressing the challenge that the settlement behavior of granite residual soil in South China during foundation pit dewatering cannot be fully understood due to its unsaturated characteristics, this study proposes and validates an unsaturated fluid–solid coupling calculation method for dewatering-induced settlement analysis. This method is implemented by compiling FISH language code within a finite difference software framework. Validation was carried out by comparing thes simulated groundwater drawdown–time response with the measured drawdown from a field pumping test, demonstrating the improved agreement of the proposed unsaturated coupling approach relative to the conventional coupling scheme. Furthermore, to elucidate the soil settlement mechanisms, a sensitivity analysis of the deformation behavior of granite residual soil during dewatering was performed. The results demonstrate that, compared to the traditional fluid–solid coupling method, the unsaturated fluid–solid coupling method exhibits superior agreement with field dewatering experiments. The sensitivity analysis reveals that the differential settlement observed in the soil surrounding a dewatering well under the same target drawdown is primarily attributed to variations in drainage consolidation time and pore water pressure dissipation. Finally, a normalized analysis correlating the dewatering depth at the well with the resulting soil settlement deformation was conducted, establishing a practical relationship applicable under similar ground conditions and dewatering durations. This analysis provides theoretical guidance for selecting appropriate dewatering schemes during engineering practice.