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

September 2011, Vol. 66 No. 9

“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 says. “Accuracy was of paramount importance. It was also such a small footprint that it would have made it difficult to initially set up one of our big rigs there.”

Railroads, right-of-ways and a 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 at 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 explains. “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 significant accuracy challenges, it was the second leg of this three-fold installation project that the Veidmark brothers, despite their extensive experience in trenchless construction, 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 says. “The plan specified two bores within relative close proximity parallel to the canal. We came to find out this was no ordinary rose garden, but rather the only one in the world where this special variety of roses are grown. This itty-bitty plot contained tens of millions of dollars-worth of these roses. If we would have tried the traditional auger bore approach, there’s a good chance we could have drifted right into this multi-million-dollar garden of roses.”

Abe reiterates the need for precision, comparing the boring process and subsequent installation at each of the three sites to that of a double-barrel shotgun.