Getting unstuck underground

Horizontal directional drilling is one of the most challenging and complex construction applications and fraught with unknowns. When one of those unknowns conspires to seize your tooling or product deep underground, your chances of recovery range from slim to none.

Chris Brahler, president and CEO of TT Technologies, has been experimenting with and developing a set of techniques that combine pipe ramming with HDD. These techniques have been developed with the help of many well known HDD contractors in the United States, says Brahler. They enable contractors to use the percussive force of a pipe ram to recover drill stem and free pipe that has become stuck underground during a pullback.

These methods are most valuable in the larger diameter bores, where more is at stake, Brahler says. But in some soils, Florida for example, where sand can leach off your drilling fluid, ramming can be helpful even on small bores. Prior to the pipe ramming techniques, the penalties for abandoning a length of large diameter casings could be severe. “They might be leaving a half-million dollars of pipe in the ground and then they’d have to spend a small fortune grouting it” Brahler says. “So we’re seeing a trend where people are taking a proactive approach with rammers on big jobs to minimize the chance of getting stuck.”

Here is a a quick rundown of these techniques:

Bore salvage
A bore salvage operation is designed to back out a stuck product pipe from the ground. Once it has been determined that the pipe is indeed stuck, a pipe rammer is attached to the tail end of the partially installed product pipe with a fabricated sleeve – but with the rammer in reverse so that its percussive force is directed up out of the hole. The free end of the rammer is also attached to a winch to assist in the process and the combined pulling force of the winch and the percussive impact of the rammer back the pipe out of the hole.

Drill stem recovery
The drill stem recovery technique is used to bail out a pilot bore that’s stuck and can be used to push the drill bit forward or back it out of a hole using the same principals as the bore salvage except that you can go in either direction. Again a fabricated assembly is used to connect the pipe rammer to the drill stem except on this assembly a plate is welded to the free end of the assembly and a threaded receptacle is welded to the plate to receive the threaded end of the drill stem. This can be done in the field in as little as two to three hours, Brahler says. Attach the pipe rammer so that the percussive effect is directed back toward the original bore starting point and you hammer the drill stem out of the hole. Or if the drill stem is still attached to the drill rig you can attach the pipe rammer with the percussive force forward and ram the drill stem while the drill rig pulls back.

Pullback assist
When your HDD machine doesn’t quite have enough power to overcome hydrolock or other underground conditions that stop movement of the pipe you can use the pullback assist technique to finish installing your product. Pullback assist can also prevent damage to your product pipe when the pulling forces needed to move the pipe exceed the tensile strength of the pipe.

With pullback assist, you simply attach the rammer to the tail end of the product pipe with the percussive action in the direction of the pullback. You can do this prior to the pullback or as soon as excess resistance is encountered. The rammer can be turned on or off as needed to complete the job.

The quicker you react to hydrolock or other conditions that seize your pipe the better your chances of getting unstuck. For that reason many contractors will hook up a rammer in a pullback assist configuration prior to the start of a job, Brahler says.

Finesse, not brute strength
The perception among drillers is that brute force solves problems, Brahler says. “People who are used to pulling pipe with a line of dozers don’t think that a little 18-inch rammer could do what their dozers couldn’t do, but it can,” he says.

Care should be taken, however, not to overuse a hammer. “If a customer is not paying attention and maintaining his pressures he can get into trouble,” Brahler says. “I know of one operator who pushed the pipe right up into the drilling rig. You have to be very careful and run the hammer at one-third power, just to finesse it, to break the hydrolock. Once you free it up for that 10 or 15 feet, you can turn the hammer off and continue the pullback.”