The project involved the construction of a back-up pipe for the Northern open sewer under the Plovdiv – Burgas railroad and Eastern ring-road. The construction of the facility was necessary to increase the capacity of the existing sewer, and secure the effective operation of the newly built Northern wastewater pumping station. The project was carried out by Stroitelna Mehanizatsia PLC, and was funded by the Ministry of Environment and Water (MEW), the European Bank for Reconstruction and Development (EBRD), and the Swiss Government.

The project was executed by a Herrenknecht EPB 2400 tunnel boring machine (TBM) and was conducted in six stages between September 2009 and February 2010. The first stage involved the construction of the starting and receiving shafts, which was followed by the installation of the TBM. Next, the TBM constructed a steel pipe tunnel. After the boring stage, the TBM and auxiliary installations were dismounted, and a fibreglass operation pipe was inserted into the steel pipe. Finally, the operation pipe was cemented into the steel jacket pipe, and the pipe entrance and exit were constructed. In total, 52 m of new sewer pipe was installed, with a diameter of 2,400 mm.

The execution of the project was quite technically complicated as the pipe was installed in close proximity to a river, and was required to travel under the railroad and ring-road without disturbing traffic. Yet, despite these challenging conditions, the project was carried out according to plan, and works were completed within the expected time frame.

Present at the opening of the new sewer were Minister of Regional Development and Public Works Rosen Plevneliev, Governor of Plovdiv Ivan Totev, and Executive Director of Stroiltelna Mehanizatsia Stefan Zhelyazkov, who is also Chairman of the Bulgarian Association of Trenchless Technology (BATT).

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Mr Plevneliev expressed his satisfaction at the speed and quality of the project, as well as its innovative use of trenchless techniques.

Similarly, Mr Zhelyazkov praised the project management. “Ivan Totev was smiling but he took his responsibility to personally oversee the execution of the work very seriously,” he said.

Mr Zhelyazkov emphasised that the project caused no interruption to either road traffic or train schedules, bringing this Bulgarian project in line with international engineering and infrastructure standards.