Ask the DP Pro

Q How can Contractors Mitigate Risk on Trenchless Pipeline Projects?

THIS RESPONSE FOCUSES on horizontal directional drilling (HDD), probably the most common method of trenchless construction. There are many other methods of trenchless excavation and most of these suggestions work regardless of methodology.

1.Know the industry standards and guidelines for the work being performed as well as for the equipment being used. Guidelines set forth by the HDD Consortium and the CGA are a great place to start. Equipment manuals should also be referenced. The time to learn about these is not in a deposition after something catastrophic has happened.

2.Understand the level of design that went into the plans of the job you are either bidding or have won. Subsurface Utility Engineering (SUE) continues to grow in our industry. For an understanding of the different levels of SUE, ASCE #38- 02 provides a great explanation. If virtually no design or a SUE level D design has been performed, the contractor should have little comfort in the information provided.

3.Consider the use of a private locating company. They use techniques including inductive sweeps to determine if other metallic lines are in the dig area. Ground penetrating radar can also be utilized to find both metallic and nonmetallic lines in the area. Ground conditions can sometime reduce the effectiveness of GPR, but the GPR technician should be able to let the contractor know if poor conditions exist. There is no “silver bullet” to identify hidden utilities, so the private locate technician utilizes a full toolbox of technologies to deliver as much information as possible.

4.Pothole all utilities at the point of crossing and leave the potholes open so that the bore head and back-reamer can be seen safely crossing the exposed facility. Unfortunately, there have been many cases where contractors have tried to find a shortcut around this process. Measuring to the top of a water valve or opening a manhole or handhole to observe the elevation of a utility only provides verification at that point and not at the actual point of crossing.

5.Plan the work and then work the plan. Develop a bore plan based on all the information collected and then follow it. If an unsuccessful shot requires a move, then start the plan again. There have been numerous cases over the last decade where the contractor potholed and then tried to bore through the pothole but was unsuccessful. Instead of reworking the plan, they simply moved 10 feet in one direction and performed the work using the old pothole information. The results of these “blind” bores were utility damages and in a couple of cases, gas explosions.

6.Document, document, document. Photographs and video of the site after locates are complete and prior to the work are invaluable to help prevent damage, as well as to tell the story of the incident if something goes wrong. This includes documenting potholing activities as well as work progress and problems along the way.

7.Perform interference checks as well as calibration of the equipment and document it. If it is not documented and something goes wrong, it will be impossible to prove it was done.

Each item listed is just a brief overview, but if these methods are employed, the worksite should be much safer and the risk of damage to existing utilities will be greatly reduced.

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