Horizontal Directional Drilling
If we could see through the dirt and asphalt, city streets and rural roads alike would look like tic-tac-toe boards with all the wires, pipes, and other conduits running beneath them. However, in most cases, the roads have been in place far longer than the tubes that run underneath them, and, with how quickly technology changes, construction workers certainly can’t dig up a section of road every time a new conduit is needed. So, how do those pipes get there? The answer is horizontal directional drilling.
Also called directional boring or HDD, horizontal directional drilling is a steerable method of digging along a prescribed bore path. With proper use of a surface-launched drilling rig, HDD will have minimal impact on the surrounding area, making it ideal for installing pipes, conduits, and cables under roads.
The horizontal directional drilling process begins with the boring of small pilot hole under the road (or other crossing obstacle), using a continuous string of steel rod. Once this steel rod emerges on the other side of the road, a specialty device called a back reamer is attached. Drill direction is reversed and the back reamer is pulled back through the pilot hole, boring it out to the proper diameter so that the pipe can be pulled through. The conduit is generally pulled through behind the reamer to ensure centering of the pipe in the newly created tunnel.
Location and guidance is critical to directional boring. Because the drilling head is underground during the process, it must be precisely guided and controlled to avoid collateral damage. One of three locating methods may be used for drill head guidance; the system used is determined by worksite requirements. Walk-over locating uses a specialized transmitter to relay angle, rotation, direction, and temperature information to the bore machine operator via an electromagnetic signal. Wire-line locating uses a magnetic guidance system to read inclination and azimuth, and also verifies location utilizing wire grids laid on the ground surface. The gyro-based locating system works completely autonomously and offers the most accurate readings over long distances.
The equipment used in directional boring is dependent on a number of factors: the diameter of the pipe being installed, the length of the run being drilled, ground conditions, soil makeup, and the above-ground surroundings. For many HDD applications, drills must be supplemented with excavators, mud reclaimers, and pumps and hoses to supply drilling fluid.
•“HDPE Pipe” – Chapman Electric, Inc.
•“Chapter 12 – Horizontal Directional Drilling” – PlasticPipe.org (PDF)
•“Directional Boring” –Wikipedia