A Unique Combination of Trenchless Technologies

A steel cast pipe with diameter of 1800 mm and length of 40 m was installed only within 8 days under 1^st class road I-V (Stara Zagora – Dimitrovgrad) with a combination of trenchless technologies.

In August 2007 the team of Stroitelna Mehanizatsia JSC, Kazanlak faced the difficult task of installation of pipe with diameter of 1800 mm. As the numbers indicate, a man can walk in this pipe in an upright position.

Until recently the construction practice in our country was unified – pipes with such diameters can be installed only with the conventional method, which is accompanied by redirecting of traffic and road excavation and sometimes by using of minor’s method with undermining and reinforcing of the tunnel.

In that case, however, we had to take into consideration the excessively intensive traffic at the construction section of Trakiya highway road junction, which has to be ready for use only after a month. Moreover, since this pipe was designed for sewerage construction, there were strict requirements of observing the project inclination of 6/1000. These are only 6 mm per running meter.

These circumstances excluded the excavations of the road and the minor’s method would have taken months. The only solution was to use trenchless technology and the only contractor who has the necessary technical equipment and expert knowledge – Stroitelna Mehanizatsia AD.

However, which one of the trenchless technologies should be used in this case?

Microtunneling ensures the project inclination but is extremely expensive and the technical equipment needed for the installation of such diameter can be leased from the producer only after few months of waiting. For now this technology has been applied only once when the metrostation was constructed near the busy road junction at the Rector’s Office of Sofia University St. Kliment Ohridski. The contractor was Microtunnelling Consortium which was founded especially for this project by Stroitelna Mehanizatsia AD, Kazanlak and Raicommerce Construction AD, Sofia. It was necessary that a non-standard solution be searched for.

The latest challenge in the field of the large diameters provoked the technical potential of the enterprise.

After a careful consideration of the existing soil conditions of the terrain, the team of engineers of Stroitelna Mehanizatsia AD proposed application of combination of solutions used with the different trenchless technologies. The same team made the design of the instrument needed for the installation and the instrument itself was manufactured by Mechanical and Welding Departments of Service Division in the company. In order to guarantee the project inclination of the pipe, specialized pipe laser Topcon was urgently delivered from USA (it turned out that the Bulgarian dealers of the production companies do not have such an instrument in stock).

Within eight days the installation was completed successfully. A Horizontal Directional Drilling machine UBI 8A/USA/ with maximum tractive force of 77 tons was used for the implementation of this installation.

The installation was implemented without any disturbance of the intensive traffic to South Bulgaria and the frontier posts to our south neighbouring countries as well as it did not impeded the construction works of the Trakiya highway road junction.

Stroitelna Mehanizatsia AD has undertaken steps to patent the method and the design of the instrument. If this patent gets registered, Stroitelna Mehanizatsia AD will be proud to record the first Bulgarian contribution in the field of the trenchless technologies.

Brief information about the contractor:

Stroitelna Mehanizatsia AD, Kazanlak is an enterprise, specialized in the field of trenchless technologies. In its corporate history the company records the largest drill jobs with respect to diameter and length implemented in Bulgaria. For nine years now the team of specialists has successfully applied trenchless technologies for pipe installation in urban and non-urban conditions.

Stroitelna Mehanizatsia AD is the only company in the country, that implements installation of pipes under deep river beds /length 230 m/. Only under Maritza river, cast gas pipes and cables with total length of near 1000 m are installed.

For the first time during the summer of 2005 the specialists from Stroitelna Mehanizatsi AD installed a steel cast pipe with the unique diameter of 1000 mm under a railway in Plovdiv.

The company has implemented complicated drill jobs on sites in Greece (gas pipeline Aliksandrupolis – Komotini, installed steel pipes with diameter of 1220 mm) and Serbia.

You can find detailed information about our company and activities at the following address: