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

September 2011, Vol. 66 No. 9

“We had to complete two bores, side by side, within two inches and maintain that same accuracy for 200 feet,” Abe says. “Think of it as a shotgun with two 12-inch barrels extending 200 feet that we needed to keep at least two feet from the irrigation canal, the lifeline to a multi-million-dollar rose garden. I was very thankful to have the accuracy of the AXIS system.”

Equipment staging and footprint was also a consideration for the Veidmark crew as they reviewed the options facing them to select entry and exit pit locations at each of the three sites. According to Abe, aside from the additional space needed to stage the various components of the AXIS system (compared to auger boring or horizontal directional drilling), the area required for excavating staging and receiving pits is minimal.

After determining locations and excavating the launch and exit pit, the SSC crew shored up the walls with metal bracing, set the laser to the desired grade and depth and lowered the leveling frame and rack assembly into the launch pit. The first 6.5-foot drill casing was then placed in the rack carriage and drilling was underway.

“It’s a relatively quick process once everything is in place,” Abe says. “Ground conditions were ideal so that wasn’t a factor. We completed the first two bores without any problems and the second in less than four hours, which is really good. We popped through precisely on target in the exit pit, then disconnected the bit, attached the pulling head and pulled the casing back through.”

Vacuum excavation
Abe explains that the vacuum excavation unit utilized by the AXIS system requires a fair amount of water to facilitate the removal of spoil. However, he goes on to say that the vacuum system ultimately enhances production rates because the need to suspend drilling operations to manually handle spoil within the launch pit is eliminated. The system also helps provide a cleaner pit environment.

Installing the casing was a breeze at two of the three locations -- bores of 200 feet and 180 feet respectively -- as the SSC crew was able to weld the entire length of casing segments together, allowing them to pull the material back through the bore path in one continuous shot. This was accomplished by digging a ditch beyond the exit pit and placing the entire expanse of material within, a strategy that wasn’t possible at the final location due to the position of the large fiber optic cable.