In the series devoted to the most popular technologies for underground construction, we have already wrote about the Milan method and the New Austrian method. Another, widely used construction technology for many of the metrostations in Sofia is the so-called open method.
What is open construction method?
The essence of the open construction method consists in the advance development of soils in a pit with slopes or in a pit with reinforced walls, construction of the tunnel or metro station in it, implementation of waterproofing of facilities and backfilling of the structure with vertical planning and restoration on the ground above it. The necessary internal constructions, rails, architectural works and installation of the technological equipment of the control and functioning systems of the metro are performed in the thus constructed bearing structures of the tunnels and metro stations. Mostly massive fortifications with high rigidity are applied, which allows the construction to be carried out in close proximity to existing buildings and facilities without endangering their integrity. In some cases, these fortifications are designed as part of the supporting structure of metro stations and tunnels.
Where it is applied?
The open construction method has been used in the first metro line – the section between "Sveta Nedelya" and "Lyulin" as well as a couple of the stations between “Sveta Nedelya” and “Mladost” neighbourhood . It is also applied in some of the Line 2 stations - "Lion Bridge", "National Palace of Culture", "European Union", "Druzhba" and others.
The construction of the extension of the third line of the Sofia metro on Vladimir Vazov Blvd is planned for 20121 when the section from the recently opened metro station "Hadji Dimitar" to the "Levski G" district will be performed. The Metro stations "Vl. Vazov Blvd.", "Georgi Asparuhov Stadium" and "Trakia" are planned to be built by open method and by the Milan method. They are part of the third stage of the construction of the third metro line, including a new 3-kilometer route with 3 metro stations, which will serve the neighborhoods "Hadji Dimitar" and "Levski G". Station "Bul." Vl. Vazov "will be built entirely in an open way. The tunnels between the stations" Bul. Vl. Vazov "and "Trakia" are planned for construction in an open method in a fortified excavation, and those between "Trakia" and the already operating station" Hadji Dimitar "- by a new Austrian tunnel method.