SENSITIVITY ANALYSIS OF GROUNDWATER FLOW AND LAND DEFORMATION DUE TO LEAKAGE AND DRAINAGE THROUGH URBAN UNDERGROUND ARTIFICIAL STRUCTURES

A series of hydro-mechanical numerical simulation is performed first using COMSOL Multiphysics (COMSOL, 2016) to analyze saturated-unsaturated groundwater flow and land deformation due to leakage (i.e., groundwater recharge) from and drainage (i.e., groundwater discharge) into urban underground artificial structures such as water pipes. An urban geologic system, which consists of weathered soil, alluvial sediment, and reclaimed soil in ascending order and has a leaking or draining water pipe above or below the water table, respectively, is considered in this study. A series of sensitivity analysis is then performed with various ranges of the leakage rate, drainage rate, porosity, saturated hydraulic conductivity, Young’s modulus, and Poisson’s ratio of the geologic media to evaluate their effects on saturated-unsaturated groundwater flow and land deformation due to leakage and drainage through urban underground artificial structures. The results of the sensitivity analysis in case of leakage from the water pipe show that the pressure head change is more sensitive to the leakage rate and saturated hydraulic conductivity, while the vertical deformation is also sensitive to Young’s modulus. On the other hand, the results of the sensitivity analysis in case of drainage into the water pipe show that the pressure head change is more sensitive to the drainage rate, saturated hydraulic conductivity, and Young’s modulus, while the vertical deformation is more sensitive to Young’s modulus and Poisson’s ratio. Hydro-mechanical numerical simulation methodology presented in this study can be utilized as a practical integrated evaluation tool to predict various hydro-mechanical phenomena, which can be associated with groundwater flow and land deformation due to leakage and drainage through urban underground artificial structures, within urban underground geologic systems and even to analyze their risk. This work was supported by the Under Ground Safety (UGS) Convergence Research Department Project of the Electronics and Telecommunications Research Institute (ETRI) funded by the National Research Council of Science and Technology (NST), Ministry of Science and ICT (MSIT), Korea.