October 2011, Vol. 238 No. 10
Features
Laser-guided System Helps Complete Three Intricate Bores
Plains Midstream Canada selected Specialized Services Company (SSC) to install sleeves at three locations to accommodate a new line being added to the underground infrastructure used to load and unload LPG from tankers and railcars at the Bumstead facility, an underground LPG storage cavern located along the Interstate 10 corridor between Phoenix and Los Angeles.
Project owner Plains Midstream, headquartered in Houston, is involved in crude oil transportation, gathering, marketing, terminaling and storage as well as marketing and storage of liquefied petroleum gas (LPG).
Situated some 2,000 feet below ground at the juncture of a major rail line and tanker truck transit point, the 133-million-gallon facility is composed of three underground salt-dome storage caverns, a 24-car rail rack and three truck racks on the surface with the capability to unload six trucks simultaneously. To expedite the loading and unloading of tankers and railcars more quickly, Plains Midstream installed an additional 6-inch diameter high-pressure gas line.
The project awarded to SSC involved installing six separate 12-inch diameter steel casing sleeves with a 3/8-inch wall thickness at three separate locations. Abe Veidmark, vice president of the auger division for SSC explained the challenges faced by the trenchless installation contractor, and the decision to use an innovative new approach for completing these intricate bores.
“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,” he said. “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, Abe, along with brother Arvid, executive vice president and senior estimator for SSC, recommended an innovative, alternative approach. Months prior, Arvid attended a demonstration where a Vermeer laser-guided boring system is featured 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 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 8-18-inch pipe at lengths up to 350 feet, although 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 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 a 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.
“The only way we would have attempted it using a jack and bore approach would have been to upsize to a 30-inch diameter bore casing, then steer the 30-inch casing back through,” Abe Veidmark said. “It was also such a small footprint that it would have made it difficult to initially set up one of our big rigs there.”
One-of-a-kind Rose Garden
Two of the three installations involved railroad crossings that required strict adherence to very narrow right-of-way tolerances established by the railroad. The first site required SSC to complete two 148-foot bores approximately 10 feet deep, while the third location — two 180-foot shots — called for crossing beneath seven separate sets of tracks, to the terminal site where natural gas is offloaded from the transporting railcars. Positioned close by was a large underground fiber-optic cable that limited the position and excavation depth of the bore pit.
“The location of the reception pit was sort of questionable, but we really didn’t have much leeway because of where the fiber-optic cable was positioned,” Abe Veidmark explained. “This was a situation that reinforced the need for pinpoint accuracy … something that would have been difficult to accomplish using traditional auger boring. We had to hit the target pretty much dead on, stopping within inches short of the cable.”
Although the two railroad crossings presented the SSC crew with accuracy challenges, it was the second leg of this three-fold installation project that the Veidmark brothers had not previously encountered … a one-of-a-kind rose garden.
“When we surveyed the second site to identify where the entry and exit pits should be dug, we discovered an irrigation canal that supplied water to this immense rose garden,” Abe Veidmark said.
“The bore plan specified two bores within relative close proximity parallel to the canal. Come to find out this was no ordinary rose garden, but rather the only one in the world where this special variety of roses is grown. This small plot contained tens of millions of dollars-worth of these rare roses. If we would have tried the traditional auger bore approach, there’s a good chance we could have drifted right into this multimillion-dollar rose garden,” he said.
Staying The Course
Abe Veidmark reiterated the need for precision, comparing the boring process and subsequent installation at each of the three sites to that of a double-barrel shotgun.
“We had to complete two bores, side by side, within two inches and maintain that same accuracy for 200 feet,” he explained. “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 multimillion-dollar rose garden. I was very thankful to have the accuracy of the AXIS system.”
Equipment staging and footprint was also a consideration for SSC’s crew as they reviewed the options facing them to select entry and exit pit locations at each of the three sites. 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 under way.
“It’s a relatively quick process once everything is in place,” Abe Veidmark said. “Ground conditions were ideal so that wasn’t a factor. We completed the first two bores without any problems, the second in less than four hours, which is really good. We popped through precisely on target in the exit pit, and disconnected the bit, attached the pulling head and pulled the casing back through.”
He noted that the vacuum excavation unit used by the guided boring system requires a fair amount of water to enable the removal of spoil. However, he said 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 described as a breeze at two of the three locations – bores of 200 feet and 180 feet (54.9 m) 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 AXIS-created 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.
“At the third location, since the fiber (cable) was in direct line with the bore path, we were limited to pulling back the steel casing in increments of 10 feet,” Abe Veidmark said. “This required us to weld each segment together in the pit, repeating the process until the entire 150-foot shot was complete. We were also required to pressure test each weld, which slowed the process down quite a bit.”
With the exception of a few minor learning-curve glitches that were quickly rectified by the AXIS system experts at Vermeer, the six bores were completed on-target, online and on-grade.
“The capability to maintain the target so precisely and the confidence to know that you will hit your end target exactly where intended is a huge advantage for the system,” Abe Veidmark said. “The cost is another advantage. I would have been very nervous to attempt this with just a traditional auger because of the 12-inch diameter. You just don’t know for sure where it’s going to go.”
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