ABSTRACT
Since its opening, in 2011, Algiers Metro has been the object of several expansion works, presenting nowadays an approximate length of 13.50km and fourteen stations. Extension E, connecting El Harrach Centre to the new terminal of Houari Boumedienne International Airport, is currently under construction and involves the execution of a 9.50km double-track TBM tunnel, as well as nine underground stations and ten ventilations shafts. Located below a busy crossroads of the Algerian capital, the Beaulieu Station, despite initially conceived as a typical cut-and-cover station, was deeply reshaped and is now characterized by a very intricate layout comprised of four open-air excavated bodies (with excavation’s spans and maximal depths of around 25m and 32m, respectively) and two large-diameter (19m) underground galleries. Its geological context, essentially composed of heterogenic quaternary sandy and clayey deposits (water table placed at a 20m depth), the urban environment of the area and the resulting need of an efficient deformation control, in addition to the impossibility of employing prestressed ground anchors, led to the adoption of a solution consisting of pile walls and several levels of robust steel strutting systems, combined, on what concerns the station’s central shaft and due to the need of quickly restoring surface occupation, with a top-down executed roof slab. In turn, the little overburden heights (OH) of the underground galleries excavated by means of the conventional tunneling method (of roughly 10m) and their proximity to nearby vulnerable buildings led to the adoption of an important soil treatment around the galleries, stiff pre-supports and primary linings, as well as of very restrictive excavation procedures, besides other additional measures. A complex ramp system was developed as a way of, apart from providing horizontal access to all excavation fronts in safer conditions, overcoming the imposed schedule constraints. This paper describes the geological and geotechnical site features, as well as the overall conception and executive procedure of such Station.
