Investigation on urban groundwater flow and construction of subsurface concrete cutoff walls interaction using a numerical modeling approach (case study: Karbala city, Iraq)

In urban development projects, it is important the interaction of groundwater-flow and subsurface-structures, including cutoff-walls. Using a modeling approach to investigate these interactions can be helpful in planning to implement and strategies to reduce the adverse-effects. In this study, the numerical-code MODFLOW has been used with HFB package to simulate the three-dimensional groundwater-system of an urban area in Iraq, taking into account the geological layering and heterogeneity and the constructed cutoff-walls. These 40-meter-deep concrete cutoff-walls have been constructed with the aim of locally groundwater-level reduction to provide an ability to build the designed constructions under ground-level. For calibration and validation of model, the measured data of groundwater-level in 28 observation wells from February 2016 to September 2018 have been used. The aim is to investigate the interaction between the construction of subsurface concrete cutoff-walls and groundwater-system based on development plans. The results show that in the development of considered phases, an increase or decrease in groundwater-level can occur up to more than one-meter compared to pre-development conditions next to cutoff-walls. For example, under the constructed phase condition, the groundwater level changes are between -0.55 (maximum drop) to 0.44 meters (maximum increase) while with the completion of all phases, these changes are between -0.06 (maximum drop) to 0.14 meters (maximum increase), respectively. Preventing the water entering to the lower parts of constructions and maintaining the stability of adjacent structures are some of the issues, which should be observed considering the technical and managerial solutions suggested in this study.