September 2021 Vol. 76 No. 9


HDD Guidance in Extremely Energized Ground

A handful of horizontal directional drilling (HDD) specialists had failed to complete a scheduled installation of fiber optics in a Greenville, S.C., project that was now more than a year overdue. Bore-path complications included two heavily vegetated ravines, a road, two restrictive railroad right-of-ways and a reinforced concrete parking lot. 

In addition, the path ran between two abandoned and filled underground gasoline storage tanks and alongside a mismarked fiber-optics line that remained up and running. Magnetic field anomalies confounded utility locators and HDD guidance systems. Regional contractors 

either refused to take the job or begged off after beginning it. 

These are exactly the types of jobs Atlas Group’s HDD division pursues. “We are called in to finish jobs other contractors can’t finish. You could say that’s our niche, drilling in hard rock, doing the most difficult jobs,” said KJ Woody, president of Atlas Group. 

Founded in 2001 in Buckhannon, W.Va., by KJ and his brother, Kyler, Atlas Group is a family-owned and operated company serving the needs of underground utility and construction customers throughout the East Coast region. HDD applications typically involve fiber, natural gas and waterline installations. 

Job specifications 

The overdue 672-foot run along a busy highway began directly beneath high-tension power-transmission lines. The massive magnetic field completely masked a typical drill string’s beacon signal. The path then descended beneath the heavily vegetated surface of a 40-foot ravine before crossing deep beneath a side road. 

Beyond the road, the surface descended again. Here the bore path crossed beneath a decommissioned railroad track and then further on, beneath two active railroad tracks. The railway company forbade any locating activity within 10 feet of the rails. 

Once past this obstacle, the surface above the path rose to an elevation beneath an old gas station’s parking lot. The bore must rise beneath the parking lot to pass between two abandoned tanks lying just before the exit point. Adding further interference was an existing fiber-optic line that lay parallel to the bore path along its full length, also passing between the abandoned gas tanks. 

Atlas was introduced to the job after finishing a separate HDD project for the same Greenville customer in similar energized ground conditions elsewhere in the city. 

Since the two sites were located close together, Woody anticipated similar problems with signal reception and interpretation. The initial BPA using Atlas Group’s own Subsite TKQ receiver confirmed it. The TKQ is a four-frequency tracker especially designed for larger rigs and longer bores with a locating depth range rated to 110 feet and tracker-to-rig range rated at 2,000 feet. 

Despite the receiver’s power and accuracy, in many of the places where Atlas crews could get signals, they couldn’t consistently trust them. 

The shallow noise floor they discovered meant even after a successful start, portions of this job would have to be either drilled blind or exposed. Obtaining a visual verification at the depths specified for this run, and working on the slopes in rough terrain, would add enormously to project time and cost. 

Ready resource 

The Woody brothers were confident that they’d succeed in spite of the job’s complexity, but they wanted to see if they could get better signal reliability. They decided to bring in Subsite rep and application specialist Brett Romer to demo the newest HDD guidance equipment. 

Romer brought a four-frequency Subsite TK RECON 4 receiver, Subsite 17T4 beacon and Subsite Commander 7 remote display, plus a wealth of knowledge. This enhanced understanding of how interference affects a receiver’s interpretation and how to use that knowledge to their advantage. 

Innovations in HDD guidance systems have made them more user-friendly and easier to learn and operate. However, interpreting what they say in actual field conditions entails a much deeper grasp of the underlying operating principles. 

Romer hooked up the Commander 7 to Atlas’ Ditch Witch JT3020 All Terrain drilling rig and calibrated the receiver. Then using both of the receivers on hand, the team initiated another BPA, comparing the results to the first BPA. Comparisons are useful because they can show, for instance, whether anomalous variations remain consistent from one BPA to the next, or if they have changed with time of day or other variables. Both instruments recommended frequencies of 29 kHz and 12 kHz to mitigate ambient interference. 

Next, the crews re-examined the noise floor for the run, determining a maximum depth of about 55 feet. Knowing they would not be allowed to perform locates near the railroad tracks while running at a depth of 35 feet, they set up the beacon for 29 B power and 29 X power. 

The 17T4 beacon Atlas was using in its Ditch Witch Rockmaster housing on this job was capable of emitting its signal in four frequencies at three field-configurable power levels. Preset frequency and power combinations can be switched from one to another on-the-fly by putting the beacon to “sleep” and restarting within a designated period of time. 

Then began the drilling. One of the benefits of the TK Recon 4 was its beacon compass. The crew no longer needed to track steering by having the receiver operator cross back and forth 20 feet at a time to verify nulls. Another benefit was its pitch-assist tracker boot, which came into play because of the rough, irregular terrain and varying slope of the surfaces above the bore. 

Day 2 

The crew got more than halfway through the full length of the run on the first day. Day two’s drilling would include the railway crossings and the pass under the rebar-embedded concrete of the old gas station’s parking lot before exiting on target. 

When crew members got to within 12 feet of the active railway tracks, they switched guidance techniques from the TK system’s walkover mode to its DrillTo mode. In spite of the distance to the receiver, the driller easily tracked bore progression to the target on his Commander 7 display. The setup had a continuously reliable signal with the bore 14 feet beneath the rails, progressing at about two feet a minute for each rod. 

The final peak of the bore path topped out about 150 feet away from run completion. The trick here would be steering the bore precisely enough to avoid the fiber optic line running alongside the bore path and the abandoned gas tanks on the other side of the lot. 

It took two hours to locate the fiber-optic line. The crews finally had success after running out an additional 50 feet of fish tape and grounding the transmitter to the air conditioner ground of a nearby business. They first detected the signal by running the unit at 13,000 Ohms. Setting the power to level 5 and using 8.01 kHz enabled them to get down to reliable reception at 5,000 Ohms. 

Despite being satisfied with their utility locator’s settings, the crews did not believe the reading it was giving them. They knew the fiber as marked was mislocated, but readings were showing it at just one foot, one inch below the concrete. 

Atlas called in a ground penetrating radar (GPR) contractor to ascertain the fiber-optic line’s true location, only to learn the crews’ readings had been almost dead on. The GPR showed it to lie exactly where they determined, but slightly deeper at one foot, nine inches. 

Despite Atlas Group’s excellent performance record, the Woody brothers agreed they still come away from every job knowing something more. 

“The best advice we have to give is why not use all your resources on hard jobs?” KJ said. “Everyone gains from each locating experience. Maybe it’s not something we use on the next job, but it adds to our expertise.”  


Atlas Group, (304) 460-7300, 

Subsite Electronics, (800) 846-2713, 

Ditch Witch, (800) 654-6481, 

From Archive


{{ error }}
{{ comment.comment.Name }} • {{ comment.timeAgo }}
{{ comment.comment.Text }}