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In this article, our HDD expert Charles Stockton explores the circumstances in which contractors are expected to foresee certain situations and potential impacts in HDD projects.

A question I’m often asked to consider by both clients and contractors is, ‘were the conditions encountered a physical condition that would reasonably have been anticipated by an experienced and competent contractor at the time of tender if that contractor had inspected all written information both publically available and made available for the purpose of tendering?’

Initially both parties needed to carefully consider if there was sufficient geotechnical information undertaken during the design to adequately determine the crossing geology.

For short crossings this may mean just one borehole on either side, and as long as there is some consistencies in these investigations, then the formation may be interpolated. If differing geology is located at either side then further investigation including boreholes and or geophysical may be required. But was there time to undertake these additional investigations and were the costs warranted?

For longer crossings boreholes at 150m-250m spacings are required and these boreholes should be approximately 5-10m offline to reduce the risk of frac-out, and drilled to 3-5m below the designed drill profile.

Other material may be available such as geological maps and historical data but it will be these boreholes that become the most reliable source of information for determining the execution methodology.

Contractors should include all borehole logs on their crossing profiles and indicate their interpretations of the formation boundaries, and use this to highlight any areas of potential risk. These risks should then be jointly discussed to understand the probability and consequence for possible impacts to the project schedule and budget.

Both parties will then need to consider if the additional information was made available post-award and was this information correctly assessed to determine if there was a material change to the information supplied at the time of tender. If so was this change correctly identified and addressed?

Finally the contractor will need to maintain accurate drilling logs, photographs and reporting that precisely captures the actual conditions encountered. An experienced third party, such as Stockton Drilling Services, can then determine what effects were due to formation and which were due to mechanical breakdown, poor tooling selection or inappropriate execution methodology.

The drilling logs can then be interpreted to establish whether the formation did differ materially and substantially from the physical conditions that should have been anticipated by an experienced and competent contractor based upon all available data at the time of tender.

Stockton Drilling Services can provide expert advice to both clients and contractors throughout all project phases and has compiled a technical guide to assist in the successful planning and execution of horizontal directional drilling works. The guide covers a wide range of topics including:

  • Current capabilities of HDD
  • Essential factors for a successful HDD
  • Integrity, maintenance and safety
  • Dealing with frac-outs
  • Avoiding damage during installations
  • Shore crossing design
  • Working in urban areas
  • Important elf geotechnical information
  • The future of HDD

Download your free copy of the technical guide at stocktondrillingservices.com.

UK-born Charles Stockton has been a part of the HDD sector in Australasia since 2003. He is the Managing Director of Stockton Drilling Services, a leading engineering consultancy specialising in HDD and other trenchless pipeline installation methods. For more information please visit www.stocktondrillingservices.com or contact Charles on 0400 623 441 and [email protected] to discuss your next trenchless project.

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