An Insight in the Mälarbanan Project : A Study of the Hydrological and Geotechnical Aspects of the Mälarbanan Project

Abstract: In “Mälarbananprojektet”, Trafikverket (The Swedish Transport Administration in Stockholm) want to expand the railway. Mälarbanan is at the present a railway that extends between Stockholm and Hovsta. The railroad will be expanded to four tracks from two tracks and the aim of the Mälarbanan project is to separate commuter trains from other trains. As there is limited space on the surface, space underneath the surface must be used. This is why it is important to determine how far below the surface the construction will have to take place, which most likely will require a groundwater drawdown. This thesis focuses on an area with two reference points in Solna. A lowering of the pressure levels normally affects the surrounding in the form of subsidences, also known assettlements​, in the ground. As the area has a clay layer believed to be around 7 m thick, and clay is sensitive to groundwater drawdowns, the drawdown must be minimal. The soil engineers have established that the maximal groundwater drawdowns should not exceed 3.0 m, as anything over 3.0 m may cause extreme settlements in the settlement sensitive clays over the next 100 years. The modelling of drawdown and pore pressure conditions is conducted in a software called ​Visual MODFLOW.​ These different groundwater drawdowns, or scenarios, computed in the settlement calculations are 0 m, 0.3 m, 1 m and 3 m. The calculations have been computed for 1, 2, 5, 20, 40 and 100 years from now. Besides settlement occurring from groundwater drawdown, settlements in the form of primary and secondary consolidation (creep) normally occur from constant loading. This requires a software for settlement calculations that takes creep effects into consideration and the software used in this case was ​GS Settlement​. The parameters necessary for the calculations are obtained by conducting CPT, collecting undisturbed soil samples for fall cone tests and CRS-tests in a laboratory. These methods are supposed to decide how and if the project can proceed.