Since 2005, the companies from GEOTECHMIN GROUP have successfully implemented a number of Sofia Metro Extension projects.

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Our activities in metro construction started by building Vasil Levski Stadium Metro Station, a Start Shaft for tunnel boring machine (TBM) and an underground connection between Vasil Levski Stadium Metro Station and the existing tunnel under Dragan Tsankov Blvd. The project was implemented by Geotechmin OOD, as a subcontractor of the Japanese company Taisei Corporation in the period 2005-2009.

Vasil Levski Stadium Metro Station is situated near the intersection of Dragan Tsankov Blvd and Evlogi Georgiev Blvd. It is entirely underground and 16 m deep. It has monolithic structure with load-bearing diaphragm walls. The metro station was built in full conformity with the relevant requirements on dimensions, architectural design and construction technology.

It comprises a station with two side platforms located at the lowest level and a three-level car park above it. The vestibule is aesthetically connected with the surrounding park area by outdoor amphitheatre stairs. In terms of tunneling technology, Vasil Levski Stadium Metro Station was built using the Milan method.

In the vicinity of the metro station, Geotechmin built a start shaft for vertical access of the tunnel boring machine (TBM). The shaft dimensions are 18/20 m and it is 20 m deep. The structure is made of diaphragm walls and reinforced with 4 rows of metal frames.

The underground connection between Vasil Levski Stadium Metro Station and the existing old tunnel under Dragan Tsankov Blvd is provided by building a 208 m long tunnel section with a longitudinal inclination of 3.75% toward Vasil Levski Stadium Metro Station. The thickness of the soil cover above the tunnel varies from 11 m at the metro station to approximately 7.6 m at the other end of the tunnel. Construction works were carried out according to the New Austrian Tunneling Method (NATM).

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In the period 2010 – 2012, Geotechmin OOD was the main contractor and Geostroy AD was a subcontractor of the project for design and construction of James Bourchier Metro Station and an adjoining tunnel section. The project was funded by the European Regional Development Fund through the Operational Programme “Transport”.

James Bourchier Metro Station belongs to the second line of Sofia Metro and is located under Cherni Vrah Blvd. It is 208 m long and 18.7 m wide. The adjoining tunnel section is 215 m long and 15 m wide.

In terms of construction technology, this metro station is one of the most complicated Sofia Metro projects. This is because it was built at a depth of 27 – 22 meters in the different sections, and because it was executed in compliance with the Employer’s requirement not to interrupt the traffic along the boulevard throughout the construction process.

The structure of James Bourchier Metro Station is entirely underground with three, four or five levels in various sections. The station, which has two side platforms, is located at the lowest level. The car park is built on three levels above the station and on two levels above the tunnel, and it forms a common structure with the station and the tunnel. Its capacity is 615 cars and its total built-up area is 21,400 m2.

Various construction methods were used in the implementation of this project. The excavation works to the bottom slab level were carried out through the Milan method.

A specific characteristic in the execution of James Bourchier Metro Station is the adoption of a pre-stressing technology. It was applied to reinforce the tunnel roof slab and partially the floor slabs in the tunnel and in the station. This method was used for the first time in metro construction in Bulgaria.

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In April 2013, Consortium “Geometro B.P.” with a leading partner Geostroy AD and members Geotechmin OOD and Metroproekt ООD started construction of a metro section towards Mladost-4 Residential District. The section includes Business Park Sofia Metro Station and a 1-km adjoining metro tunnel.

The project was implemented on a “design and build” basis in one of the fastest-growing residential areas in Sofia and connects Mladost-1 Residential District to Business Park Sofia in Mladost-4 Residential District. The so-called “Milan method” was applied in the construction of the metro station and the tunnel, which are entirely underground. A specific characteristic in the implementation of Business Park Sofia Metro Station was the requirement to build special supporting structures in those sections where the tunnel goes under two existing underpasses and beneath the Banishka riverbed.

The interior of Business Park Sofia Metro Station is conformed to the station’s main function – to serve both citizens of Mladost District and Business Park Sofia’s employees. Besides, the metro station offers an underground car park with a capacity to accommodate about 100 cars. The underground section is expected to transport approximately 45,000 passengers per day. Its construction is funded under the Operational Programme “Transport 2007-2013” and co-financed by Sofia Municipality.