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TAP Crossing of Axios River – a World-class Engineering Feat

04 June 2018

In February 2018, TAP completed a 1,820m-long horizontal directional drill for the crossing of the Axios river, thus achieving a world-class engineering feat regarding such a large volume of directed bore pipe in one length.

The feat

At kilometre point 375 of the pipeline route, near the Greek village of Elaiousa in Central Macedonia, TAP’s contractors and their engineers faced a construction challenge: the crossing of Axios (or Vardar), a river running 380km through the Balkans before flowing into the Gulf of Salonica.

The challenge included constructing a 1,820m-long pipe section, comprising 48'' (or 1.2 meters) line-pipes in diameter, and accommodating the welded pipe stretch in one go. And on top of that, the team had to build this pipe string along a curved section of the Right of Way, within a floatation trench passing below a provincial road.

The preparation

It was a very well-planned and controlled installation process that took over 36 hours and was completed with zero impact on either the local communities or the environment.

The planning and design for the crossing began in July 2017, when the relevant geological investigation and geophysical studies were conducted. This phase enabled the team to create additional bore holes and develop an optimal drill profile that could be enlarged to 62'' in diameter, so as to better accommodate the 1,820-long pipe string.

Drilling and reaming operations took place between mid-November 2017 and mid-February 2018, using the best equipment for horizontal directional drilling, i.e. a 400-tonne rig with reaming tools designed specifically for the project in order to minimise rotation and pull forces.

The protagonists

TAP’s contractor for lots 2 and 3, Bonatti & JP Avax, along with their own drilling contractor, "Horizontal Drilling International (HDI)," provided the expertise and resources to apply best drilling practices for this technically challenging project to be concluded in a most effective and timely fashion.  

 

The reward

For all parties involved in this project, the reward was delivering a job well-done – indeed a world-class construction achievement:

  • Forces recorded during installation were far below the figures predicted: average pull force of only 40 tonnes, with the maximum staying below 80 tonnes, meaning that the job was performed in even better terms than expected.
  • Everyone went home safely, albeit a bit muddy.