Trenchless technologies offer environmental solutions for the rehabilitation of bottom discharge pipes of the dams in Bulgaria

29 November 2019

The environmental solutions that trenchless technologies offer for rehabilitation and construction of bottom discharge pipes of dams were in the center of a presentation done by Stefan Zhelyazkov, chairman of the BATT during a Roundtable on “Management and Safe Operation of the Dams in Bulgaria” held today. The event was organized by the State Agency for Metrological and Technical Supervision in partnership with the University of Architecture, Civil Engineering and Geodesy.

In Bulgaria, the bottom discharge pipes of small dams, most built in the 1950s and 1960s, are in worst condition, Zhelyazkov said, pointing out that the causes of their malfunction could be: lack of tightness due to displacements in joints and cracks, as well as reduced or complete lack of conductivity due to the ingress of roots in the pipe, the presence of deposits, inlays or collapses.

Replacing the bottom discharge pipes by excavation technology is very costly and time-consuming as it requires complete drainage of the dam reservoir, partial removal of the dam, including the clay core, installation of a new pipe, and restoring of the clay core and the dam on the whole.

Worldwide, the practice requires the use of "trenchless technology" by which the rehabilitation of pipes is much more efficient because the work is carried out in a shorter time with minimal mechanization and without digging up the dam. In cases where the existing bottom discharge pipe is in relatively good condition - structurally sound but with leaks from the joints, a partial rehabilitation is applied only to the compromised sections. When longitudinal cracks, deformations and large displacements are present, a rehabilitation of the entire facility is applied. If the existing bottom discharge pipe is completely compromised or it is not accessible, a new bottom discharge pipe is built by a combination of trenchless technologies.

Stefan Zhelyazkov presented a video showing the installation of a duplicate bottom discharge pipe of “Topolovo 2” dam, where Stroitelna Mehanizatsia AD, a member of the BATT, applied a combination of trenchless technologies "Horizontal Directional Drilling" and "Pipe Ramming". He explained that the rehabilitation of the bottom discharge pipe of dams by trenchless technology guarantees complete cessation of leaks, improvement of its hydraulic properties and wear resistance, as well as prolongation of its service life by 50 years and more. An additional advantage is that all trenchless operations are carried out as emergency repairs, without the necessity to elaborate a project under the SPA [Spatial Planning Act], which would take a significantly longer time.

In conclusion, Zhelyazkov added that Bulgaria should borrow the world experience by applying an ecological approach to the rehabilitation and the construction of bottom discharge pipes of the dams in the country, as only the trenchless technologies offer.