MODELOWANIE PRZEPŁYWU WÓD PODZIEMNYCH PODCZAS ODWADNIANIA WYKOPU STACJI DRUGIEJ LINII METRA W WARSZAWIE

Abstract

GROUNDWATER FLOW MODELLING DURING DEWATERING OF STATION PIT OF THE SECOND LINE OF WARSAW SUBWAY

Within the Second Subway Line 28 stations will be constructed, 13 of them are localized on the postglacial plateau area and the rest of them in Vistula Valley. At the first stage, central part of subway line of 6 km long, consisting of 7 stations, i.e. Rondo Daszyńskiego, Rondo ONZ, Świętokrzyska, Nowy Świat, Stadion and Dworzec Wileński, has been constructed. The paper presents the example of groundwater flow modeling for the design of the pit station B-10 named Rondo Daszyńskiego. The pit station of the depth of 20 m, will be immersed below the roof of usable aquifer. Preliminary conception of the pit excavation assumed dewatering its inside with the use of cut-off walls to the depth of 10 m below pit bottom. The modeling were performed to answer two following questions: (1) what will be the discharge capacity during dewatering? and (2) will cut-off walls reduce the depression cone to protect subsoil settlement under existing buildings? The numerical modeling of the pit excavation dewatering was performed with the use of FEMWATER numerical program – A Three-Dimensional Finite Element Computer Model for Simulation Density-Dependent Flow and Transport in Variably Saturated Media from the range of GMS (Groundwater Modeling System). The simulation was performed for the case of 10 m depth of cut-off walls and additionally for the depth of 5 and 15 m below the pit bottom. Despite that cut-off wall was taken into account, simulation results indicated considerable discharge capacity and decreasing of piezometric pressure in surroundings. These can be dangerous for groundwater resources and settlement of nearest buildings subsoil. The results of modeling can make the decision to realize the station pit with the lateral injection barrier in the zone between cut-off walls.