Challenging Fiber-Optic Installation in Idaho

Challenging Fiber-Optic Installation
As the need for trenchless construction with less disruption and minimal footprint has grown, so has Meridian, Idaho-based Track Utilities.

In addition to the company’s headquarters in Meridian, the trenchless specialist also has locations in Jerome and Chubbuck, Idaho, and Libby, Mont., and specializes in turn-key utility installations within a trade territory encompassing nearly half of the western United States. In 2010, Track Utilities increased HDD capacity with the addition of several new Vermeer horizontal directional drills and skilled directional drill operators. The strategic move has allowed the company to engage several large trenchless projects simultaneously.

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With a growing population and demand for energy steadily increasing, longtime Track Utilities customer Idaho Power is demonstrating its commitment to providing nearly half a million customers with abundant and affordable electricity most efficiently. The Boise-based energy provider is making significant investments in improving infrastructure and maximizing energy generation.

Just one of many examples is a project recently completed by Track Utilities that will enhance the transmission network extending from its Shoreline hydroelectric power plant to four nearby substations within the Boise metro area. The intricate and challenging infrastructure upgrade involved installing more than 25,000 ft of new fiber-optic cable through some tough drilling conditions that included rock, a river crossing and an underground maze of existing utilities.

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The Case for Trenchless
Having completed many underground jobs in Boise and the surrounding area, the underground pros with Track Utilities were very much aware of the challenges they faced in advance. Track Utilities directional drilling manager Jeff Sorenson and project manager John Hilton worked in concert with engineers from Idaho Power in devising a drill plan to link the four substations with the riverside hydroelectric plant. The result was a “connect-the-dots” diagram that would affect the pulse of Idaho’s capital city. Selecting the most effective and efficient installation method with the least intrusive impact was the first order of business.

“There were many factors that led us to choose HDD,” says Sorenson. “The first major obstacle was a river crossing, followed by a slight uphill elevation en route to the first of four substations; all of which are located in the heart of midtown Boise. The majority of the bores affected both residential areas and several businesses in the mid and eastern parts of the city. Disruption was a big concern, and we knew that by using HDD we would be able to minimize the footprint and inconvenience to residents and businesses would be minimal. It kept us from having to tear out a lot of asphalt, sidewalks, streets, etc., unnecessarily.”

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And then there was the cobble. Both Sorensen and Hilton, who orchestrated the mechanics of the job, have extensive experience with the tough stuff. It wasn’t that the conventional open-cut trenching approach would have been incapable of handling the cobble; but given the importance of minimizing footprint and lessening intrusiveness, HDD definitely held the edge.

“This whole valley is cobble,” Sorenson says. “The soil conditions around here are horrible. Cobble presents a unique set of challenges for open-cut trenchers. There’s a lot of sand content in cobble formations, so when digging a trench, it needs to be about twice as wide as it does for other soil conditions; primarily because sand has a tendency to slough away and won’t compact. This wasn’t as much of a concern with horizontal directional drilling, because you can control that process with drilling fluid.”

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Lastly, the existing network of underground utilities; an elaborate collaboration of water, sewer, gas and other service lines that would have challenged even the most accomplished track trencher operators. City records were most beneficial in helping pinpoint individual lines; yet Sorensen and Hilton were well aware that a fair amount of potholing would be required.

Under the River & Through the Streets
The drill plan — consisting of multiple bores of varying length, depth and plenty of 90-degree angles — literally zigzagged the city. Sorensen and Hilton deployed a quartet of Vermeer drills, each model carefully selected based on features, capabilities and specifications that best matched specific bores.

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“The primary criteria we used to select specific drill models to use on the job were space and length of bore,” Sorenson says. “In many areas we were limited by the amount of room we had for setup, so we chose drill models that could fit the confined space requirements, yet still have the capacity to complete the bore. It all worked out very well, and helped expedite the completion of the job more efficiently.”

They chose a Vermeer D16x20 and D24x40 Series II Navigator horizontal directional drills for most of the shorter shots and those originating in congested setup spaces; a D36x50 Series II Navigator drill model for mid-range bores; and lastly, a D80x100 Series II Navigator drill for the river crossing and several of the longer shots.

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“The complexity of the bores, a combination of challenges and corresponding difficulty made this challenging but really not all that unique from many others we’ve completed,” says Hilton. “Each bore was unique. Some of them were on curves; many had angles that required several hand holes. Others had to be super deep to safely clear existing obstacles; and on top of everything else, there was the river crossing. The drills we selected were ideal for the conditions. We needed equipment that was small enough to get into tight spaces, yet had the power to efficiently bore through rock.”

The drills were outfitted with a series of single roller cone pilot bits along with crusher reamers, split cones and some split cone rock hole-openers for tooling. Sorenson estimated that approximately 8,000 ft of the 25,000-ft total was completed using the D80x100 drill. In addition, a Vac-Tron CS 800 wet/dry industrial vacuum with 800-gal capacity played a key role in locating existing utilities and avoiding mishaps.

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“I had a pothole crew incorporated with many of the drill crews so we could keep the drills running all the time,” Sorenson says. “The potholing was very extensive, just because of all the laterals and a congested network of utilities.”

Material specifications called for installing a combination of 4- and 6-in. sleeve to house the 1-1/4-in., 24-count fiber-optic cable. The 4-in. sleeve was Schedule40 SDR11 roll pipe; the 6-in., SBR9 HDPE. A fairly thick mixture of standard bentonite drilling fluid was introduced to assist in preserving the integrity of the bore path in the sand/cobble composition.

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Bores ranged from 100 to 800 ft at depths in the 12- to 15-ft range for the majority of the cobble shots; the exception being the river crossing that extended some 1,300 f at a maximum depth of 47 ft beneath the swiftly flowing current of the Boise River. The river crossing presented a unique challenge; one of many difficult to predict, and required some improvisation by Hilton and his crew.

“When John [Hilton] and I first surveyed the job, the water level was low,” Sorenson says. “We could walk across the entire width of the river. But when we started the job, it was shortly after the winter snowmelt and the river, which is normally about knee deep and no more than 300 ft wide was raging. The gates to the dam had been increased to accommodate for the melt, and the river was flowing at about double the width, and was 12 to 15 ft deep. Crew safety was a big issue. So we had to devise an alternative plan for using the locator to track the drill head on the crossing.”

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So Sorenson and Hilton paid a visit to the local equipment rental facility to secure a boom truck with an 80-ft arm and attached cage. With the boom truck positioned on a bridge above the swiftly moving current, a member of Hilton’s crew climbed into the protective cage and was hoisted out over the river to keep tabs on the forward movement of the drill head as it progressed along a 1,300-ft journey some 45 ft below. After mitigating some locator interference created by the bridge’s steel girders, the crew member — positioned above the swift river flow — helped guide the D80x100 drill operator successfully beneath the raging river above and safely to the next launch site on the other side.

A successful backream to upsize the circumference of the 6-in. bore to 12 in. helped to ensure that the integrity would be maintained as the long stretch of pipe was pulled back through. This shot, in addition to a couple of the longer bores, were the only ones that required backreaming. In most cases, the bores were short enough in length that the product was pulled through the path without incident.

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It took just a little over two months for the Track Utilities crews to complete the power infrastructure upgrade, an initiative that will deliver abundant and affordable energy most efficiently to the good folks of this progressive capital city well into the future.

Randy Happel is a features writer with Two Rivers Marketing, Des Moines, Iowa.

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