METRO ALGIERS LINE 1, EXTENSION "A", HAMMA-HAI EL BADR, GAAMA Facts Project Description Execution of the second section of line 1 of the underground railways in Algiers. The project comprises the execution of four underground railway stations including 4.1 km of tunnels and 16 ventilation structures. Construction started with the driving of five starting pits from which tunnel driving then started simultaneously at several locations using the New Austrian Tunnelling Method (NATM). The tunnels are driven using excavators with gunned concrete infill and inner shell executed in a second step. The tunnel is executed impermeable to press water without drainage with sealing foil and watertight concrete bottom. Three to four tunnel tubes are driven in parallel alternately from starting pits loca

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