Employer: Ministry of Transport, Bulgaria (financing – European Investment Bank and Kuwait Fund jointly with MAK/ADMAK Consortium)
Contractor: Geotechmin OOD
Project implementation period: 2002 – 2006

Description of the project:
Geotechmin OOD started participating in the reconstruction and extension of Sofia Airport by implementing the project “Strengthening of the Iskar River – South of Sofia Airport” in the period 2002 - 2004.

From 2003 to 2006, Geotechmin joined the construction of a New Runway System as a main subcontractor of the Consortium M.A.Al-Kharafi & Sons W.L.L. & ADMAK General Contracting W.L.L. From 2005 to 2006, Geotechmin took part in the construction of Terminal 2 at Sofia Airport as a subcontractor of the Austrian company STRABAG AG.

Two subprojects were executed within the New Runway System project: Civil Works on a New Runway System and Correction of the Iskar River.

The following construction works were carried out without interrupting ongoing airport operations:

• Excavation, backfill and construction of a new runway system including runways, taxiways and roads with a total area of 60,000 m2, construction of two deicing platforms, a drainage system and landscaping
• Correction of the Iskar River
• Landscaping around Terminal 2 and foot pavements

The alignment of the new runway runs 210 meters north of the old one and crosses the Iskar River. Its eastern part falls within the area of a former gravel quarry in which an artificial lake was formed. It reached a depth of 14 m and its water volume exceeded 6 million m3. The lake needed to be drained before building the new runway system. Geotechmin’s experts decided to divide it into two cells by constructing a rock-fill embankment and then to dewater only one cell. Owing to this far-sighted decision, only 1 million cubic meters of water were drained. The dewatering was done by a floating pump station with a capacity of 1,100 l/sec and a piping system for diverting waters to the other side of the embankment. On-site activities continued with cleaning the quarry bottom, construction of subsurface drains, excavation and filling works, laying of concrete.

Geotechmin’s innovative approach was further demonstrated in the second subproject Correction of the Iskar River. The construction works commenced with temporary diversion of the river from the area which needed to be corrected. This was achieved by building an inlet canal for diverting river waters to the lake behind the rock-fill embankment and an outlet canal for subsequent returning of these waters into the Iskar River beyond the correction area. The dewatered riverbed was then strengthened with three different types of lining: a reinforced concrete lining with geogrids (under a bridge which was being built at the same time), lining with RENO mattresses on the riverbed (in the sections immediately upstream and downstream of the bridge structure), and rock lining (for the remaining part of the correction).