Sensitivity Analysis of Sediment Deposition Characteristics and Management Efficiency in Deep Drainage Tunnels Based on Invert Geometries Using OpenFOAM

Deep drainage tunnels face significant limitations in field-scale experimentation and high-resolution monitoring due to their structural characteristics, such as large diameters, long distances, and extreme depths. Consequently, the importance of numerical simulations for precisely evaluating sediment behavior within these tunnels is increasing. In this study, we numerically reproduced the processes of sediment transport and deposition under free-surface flow conditions using sedInterFoam, an OpenFOAM-based three-phase flow solver. Initially, the validity of the vertical-velocity and sediment-concentration profiles was established by comparison with prior hydraulic experimental data. Subsequently, the model was applied to a numerical domain based on a conceptual schematic that simplifies the overall structure of the deep drainage tunnel system. For the simulation, a representative cross-section was established with a top width (B) of 0.60 m and a depth-to-width ratio (H/B) of 4. A total of 27 scenarios were configured, using flow rate, inflow sediment concentration, and invert cross-sectional shapes (U-shaped, trapezoidal, and base-type) as design variables, to perform a sensitivity analysis of their impact on sediment management efficiency (η _manage). The efficiency index (η _manage) was defined as the ratio of the sum of the mass discharged at the tunnel outlet (M _outlet) and the mass captured in the sump (M _sump) to the total sediment mass entering the system (M _inflow). The results indicated that, compared with the base section, both the U-shaped and trapezoidal sections facilitated the formation of a continuous low-velocity zone at the center of the invert, resulting in a thick central sediment bed and stable capture performance. Furthermore, the sensitivity analysis revealed that the cross-sectional shape is the most dominant factor influencing variations in sediment management efficiency. These findings provide a quantitative basis for selecting optimal cross-sectional geometries and dimensions during the design phase of deep drainage tunnels. They are expected to contribute to the establishment of proactive maintenance strategies during the operational phase.

 

Keywords: Deep stormwater drainage tunnel, Sediment management efficiency, SedInterFOAM, Multiphase flow

 

Acknowledgement: This work is financially supported by Korea Ministry of Climate, Energy, Environment(MCEE) as 「Technology development project to optimize planning, operation, and maintenance of urban flood control facilities)(RS-2024-00397821)」.