Threading The Needle: Precision Boring Required For Project At Underground LPG Storage Facility

September 2011, Vol. 66 No. 9

“It wasn’t so much the ground conditions or pitch, but rather the pinpoint accuracy of the line grade we needed to achieve for us to succeed,” Abe says. “When installing smaller material with standard auger boring, it is nearly impossible to steer with the accuracy required for all of these bores. In all likelihood, there would have been a good deal of drifting [with auger boring], something inherent with this method for shorter distances. All of these bores were less than 200 feet.”

Precision-fine boring
After reviewing the specifications and intricacies they would face at each of the three sites, Arvid Veidmark, executive vice president and senior estimator for SSC, recommended an innovative, alternative approach. Months prior, Arvid attended a demonstration facilitated by trenchless experts with Vermeer highlighting a new laser-guided boring system that had the capability to complete smaller-diameter bores with pinpoint accuracy and strict on-grade precision. Although designed primarily for sewer and water projects, the two felt the AXIS guided boring system was just the answer they were looking for.

AXIS is a pit-launched trenchless installation method designed to achieve precise, on-grade accuracy while eliminating some of the difficult steps associated with other installation techniques. The system was designed to install 8- to 18-inch pipe at lengths up to 350 feet though larger diameter and longer length bores have been completed. AXIS is also capable of maintaining the strict tolerance and accuracy required for the types of installations facing SSC as specified in the Plains Midstream job. The system requires an entry pit where the core of the AXIS system is placed, composed of the rack, drill casings, drill head and pipe laser. Located outside the launch pit is the vacuum power unit, vacuum tank and the rack power unit.

Once lowered into the pit, the drill head, with self-contained camera connected to a monitor on the operator console, projects the laser beam on the target. With the camera viewing the laser beam on the target, the operator can accurately monitor the target grade and make adjustments, ever so slightly, along the bore path, if the drill head begins to move off course. Rotation and thrust from the carriage assembly resumes as the first drill casing is pushed through the hole, and the process is repeated with subsequent sections of drill casing until the drill head reaches the exit pit.