Tel Aviv, Israel has the largest economy per capita in the Middle East. In recent years, the increasing demand for improved mobility has resulted in the fast-tracked development of the city’s mass transit system.
The proposed system includes three metro lines (M1, M2, and M3) and three light rail lines (Red, Green, and Purple). The Green Line is a light rail project that belongs to the mass transit network.
In this article, the main aspects concerning two underground stations belonging to this project will be presented as case studies, focusing on the 2D numerical analyses performed with the Finite Element Method-based software PLAXIS 2D (Bentley Systems, Inc.).
The aim of this article is to demonstrate the suitability of 2D FEM analyses in metro station outer boxes structural element design (even in demanding conditions) with specific reference to the Arlozorov West Station and Rabin Station.
The Green Line Project
The Green Line is a light rail line that will connect the southern portions of the Gush Dan metropolitan area. It represents one of the main solutions for mobility development along the Mediterranean coast, facilitating accessibility to university and production areas. The light rail line will have a length of approximately 39km (4.5km underground) and 62 stations of which four are located underground. Two of them are the ones that will be presented in the following as case studies.
Arlozorov West Station
The Arlozorov West Station has an outer box dimension of about 23m x 197m with a depth of approximately 27m. The excavation will be performed with the cut and cover technique, and the permanent structures of the station will follow the bottom-up construction procedures. The diaphragm walls reach the depth of -40m a.s.l. and their thickness is 1.2/1.5 meters. Four levels of steel struts are designed as a support system: circular hollow profiles with a diameter of 914/1219mm and thickness 16/25mm spaced 3/5m. The standard cross section is completed by a temporary concrete slab at bottom excavation level (200cm thick) and a steel truss structure at ground level that acts as a deck to ensure the urban road system operativity during the construction activities (Figure 1).
The following paragraphs present the analysis of section L-L (refer to Figure 2), located between 4-story buildings in the west side and the future Hagag Tower on the east side (currently only the excavation of the tower’s underground floors and its foundations have been executed). The distance between the future tower and the station is 7.5m, and the foundation of the building reaches -7.40m a.s.l. (about 17.5m from surface).
Geological and hydrogeological conditions are coherent with results of the investigations performed in the area: the geology is mainly characterized by stiff and calcareous sand and the Hardening Soil Model has been used in the analyses to provide reliable results in terms of deformations. Groundwater table during construction period is located at +1.5m a.s.l., approximately 9m below ground level.
Different structural elements have been used in the model (PLAXIS 2D – Reference manual), to represent the concrete diaphragm wall and slab structures (plate elements) and steel elements (i.e., struts and steel deck modeled with node-to-node anchors).
The PLAXIS 2D model described above is reported in Figure 3.
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