Innovative Technologies

The modern technologies for construction and rehabilitation of underground pipeline infrastructure enable implementation of the installation and rehabilitation activities with minimum excavation or without such. In Bulgaria, innovative technologies like Horizontal Directional Drilling, Microtunnelling, Pipe Ramming Using a Pneumatic Rammer, rehabilitation using the methods Cured-in-Place Pipe and Spirally Wound in Place Pipe, etc. have been more and more widely applied for over 10 years.
Their first steps were back in the 1970s and at the moment they are widely used in the developed countries and they have been applied in our country for over 10 years. Such a technology was used for the first time in Bulgaria by a water supply and sewerage team in Razgrad in 1998.
Today, the modern innovative technologies provide economically efficient solutions of big and complex problems of the underground infrastructure, with minimum damages incurred on the social life and the environment.
Basically, they can be divided into technologies for installation of new pipelines and technologies for rehabilitation of existing pipelines.

TECHNOLOGIES FOR INSTALLATION OF NEW PIPELINES are used when a new pipeline has to be installed without excavation of the whole section, but only by making small technological pits at a fixed distance.

Frequently used and recognized in our country are some technologies like:

Microtunnelling: It is applied for installation of sewer pipes with diameters from ø 250 mm to ø 2500 mm, when keeping inclination with high precision is necessary. Installation at a curvilinear path is also possible. The technology is similar to the one which is used for the construction of the tunnels of the metro by means of a tunneling shield, but at a reduced scale.

Horizontal Directional Drilling: The technology is suitable for installation of new HDPE (high-density polyethylene) and steel pipelines with diameters from ø 32 mm to ø 1500 mm and lengths from a few meters to more than 500 m, in various soil conditions, including solid rock. The installation is implemented along a preliminary set path and at a depth of up to 25 ÷ 30 m.

Casing Pipe Ramming Using a Pneumatic Rammer: This method is suitable for installation of steel casing pipes with diameters from ø 250 mm to ø 1800 mm and lengths of up to 60 ÷ 70 m in cases of little covering on the crown of the pipe and when it is necessary to guarantee that the danger of collapse of the road surface above the installation path is completely eliminated, for example at railways crossing.

Soil Displacement Hammer (known as "Mole"): The technology is suitable for installation of new pipelines (or pulling of cables) with lengths of up to 25-30 m and pipe (cable) diameters of up to ø 160 - ø 200 mm. It is applied mainly for installation of house connections, road crossings. It is also applied as a part of an installation for trenchless change of existing pipelines using the technology "crushing of the existing pipe and simultaneous pulling of the new one."

Screw drilling: This is a simplified version of "Microtunnelling" suitable for installation of casing and sewer pipes with diameters from ф 200 mm to ф 1000 ÷ 1200 mm and lengths of up to 40 ÷ 50 m, when the requirements for inclination and favourable soil conditions are not so rigid.


Spirally Wound Pipe: A modern technology suitable for rehabilitation of sewerage and other gravity or low pressure pipelines. It is based on the principle of “in-place” pipe production from continuous plastic factory manufactured strip of high stiffness and low weight inside the existing pipe. The process is implemented through the existing manholes, without any excavations.

Cured-in-Place Pipe: One of the innovative technologies for pipeline rehabilitation, which is most widely applied around the world. It is used for rehabilitation of pipelines, deteriorated as a result of corrosion, for old or dislocated seals of the couplings, presence of cracking, crashing of the material. The technology is suitable for pipelines made of pipes from different materials - steel, asbestos cement, cast iron, reinforced concrete, etc. Rehabilitation is implemented as a hermetic liner is installed on the inner surface of the old pipe and it firmly sticks to the existing pipe. The technology guarantees complete elimination of leakages and improving the hydraulic properties of the pipe. It is the simplest modern technology for rehabilitation.


Inspection of underground pipelines
The inspection of underground pipelines is an irrevocable part of the preliminary studies during the rehabilitation of water supply and sewerage networks, as well as concomitant activity during the implementation of the rehabilitation works. It is implemented by means of a special mobile operator station, equipped with modern remote controlled CCTV (closed circuit television inspection) robot-camera. Due to the high resolution of the camera objective, detailed information about the pipeline condition is obtained. This allows a precise location of shifts, unsealed and deteriorated sections of the pipeline. The customer receives a soft copy of the full record with detailed information about the type and the material of the inspected sections, diameters, inclinations and the reasons for the reduced flow capacity of the pipeline and the water losses. After analysis of the information, a professional statement and a complex solution for structural restoration of the functionality of the deteriorated pipeline are provided to the contracting authority.


Application and advantages of TV inspectionт

Application and advantages of TV inspection Possibility for inspection of pipelines with diameters from 100 mm to 1500 mm and lengths of up to 300 m without additional revision shaft. Electronic control of the camera in the pipeline from the surface. Automatic camera objective focusing in the pipeline. Automatic logging (special software) of connections, cracks, obstacles, unregulated water flows and other interventions inside the pipeline. Automatic logging of lengths and inclination of the sections under inspection. Situation visualization on a color monitor: detailed information about the pipeline’s size, material, flow direction, length, inclination, as well as every logged event with exact position, type, dimensions, date and time. Video recording on a DVD. Possibility for an automatic Protocol issuance with detailed information from the inspection, applied to the technical documentation of the equipment. Impossibility for manipulation of the results from the inspection.

There are other modern innovative technologies but they are either applied in combination with the main ones, or at the moment still haven't been applied in the country.


For the contracting authority:

  • short implementation time
  • installation of communications under obstacles, where it is impossible or too expensive to use the conventional technology for installation
  • very small job site - 1 ~ 10% of the size of the conventional
  • minimum mechanization - only a few construction machines
  • minimum excavation works - 3 ~ 5% of those of the traditional technologies
  • minimum risk of damaging the existing communications
  • high rate of safety during work
  • minimum quantity of materials for recovery of the road surface
  • no expenditure for repairs for the next 10 years

For the society, business and ecology:

  • CO2 emissions are reduced - directly up to 3 times, and if we take into account the additional emissions resulting from the traffic jams and alternative routes - 50 times! The expenditure for implementing construction activity is not only direct but also indirect (secondary). Only one example: the quantity of released CO for our model site.
  • the ordinary work of the companies near the job site is not disturbed
  • disturbances of the traffic are avoided
  • minimum noise and pollution levels
  • the normal daily life of the people living in the area is not disturbed
  • there is no large scale excavation of streets and pavements
  • trees and parks are not damaged
  • valuable historic monuments and buildings are not damaged


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