By Shane Darville, P.E., CFEI
Horizontal Directional Drilling (HDD) has surged in popularity with the ability to install miles of gas lines, fiber-optic cables, and other pipelines. All the while without having to dig trenches the length of the pipelines. HDD operations can be complicated because the operator has to navigate three-dimensional cable systems. These cables can be sewers lines, water lines, gas lines, and other unmarked pipelines. Combustible gas detectors can alert the operator if a gas pipeline has been punctured. Electrical sensors can detect shorts to the ground if an electrical conductor is exposed by the drill. Sometimes the drill only nicks the conductor, and the electrical sensors fail to pick up the shorts. Also, these current sensors are not able to detect plastic pipelines like PVC used for sewer lines or electrical conduit.
Some of the most serious incidents with HDD are related to cross boring a plastic pipeline. When a plastic line is a sewer line and the cross bore is noticed when the sewer begins to back up. This can also lead to trouble if a plumber runs a root cutter down the sewer line and ruptures the gas line the HDD operator installed. There are times a plastic line is an electrical conduit, and a drill bit nicks the conductors, there is not a detectable short to ground, but over time the conductor deteriorates which can result in an explosion. The figures below show an electrical conductor that was hit by an HDD operation. Our experts traced the drilling pathway through a neighborhood and found exactly where the HDD operator hit the conductor.
Figure 1. Crossing Point Between Existing Electrical Conductor and Fiber-Optic Line Installed by HDD.
Figure 2. Impact Point on the Electrical Conductor.
The experts at Bison Engineering use their knowledge in horizontal directional drilling and this industry to investigate each incident. Bison prides itself, making sure the engineers are familiar with the codes and standards from the National Utility Contractors Association, as well as procedures from the Common Ground Alliance.
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