River Challenge

Sept. 1, 2009

The soil conditions in Idaho create challenges that can leave the most experienced horizontal directional drilling (HDD) contractors scratching their heads in disbelief. That was the case for Earth Energy when that company was faced with the task of installing a 24-inch HDPE water line under the Boise River in downtown Boise, ID.

Soils in this part of the state can range from cobble to sand to rock formations all within a 500-foot bore. So it takes a great deal of planning, patience, and experience to complete underground installations under such conditions, and that’s where Earth Energy comes in.

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Earth Energy was formed in 1989 by Erv and Darrin Hoge. They began by placing drops for the phone company, which included plowing, trenching, splicing, and a variety of underground operations. In 1993, the company expanded into larger utility installation projects, and today the company specializes in providing HDD services for the installation of fiber optics, phone, power, gas, water, and sewer lines. Earth Energy also provides HDD services to the petroleum and gas industries, along with remediation of hazardous waste sites.

River Project
Earth Energy was contracted by United Water, the local potable water utility in the Boise area, to install a new 24-inch HDPE water main across the Boise River. The water main was being installed to provide a more reliable water source and line pressure to existing and new customers in the rural part of northeast Boise.

“Earth Energy has a long-term relationship with United Water and their prime contractors to provide directional drilling services on new large-diameter water mains and the smaller service lines to commercial and residential customers,” says Erv Hoge.

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Prior to providing a bid for the project, Earth Energy conducted a series of site visits to determine the general layout of the area, meeting with the local utility companies to determine the location of existing underground facilities that may be within the proposed bore path. One of the primary utilities was an existing gravity sewer main crossing the river near the vicinity of the proposed bore.

Another critical issue was the location of the utility easement along existing residential homes, which limited the amount of room between the sewer line and private property. Once these boundaries were determined, Earth Energy could proceed in developing a running line and profile for the new water main.

The 640-foot bore would pass under the Boise River and a parallel stream, designated as a sensitive trout fishery, as well as a wetland area. Earth Energy was asked to maintain a minimum depth of 15 feet below the bottom of the stream and minimum setbacks were required away from the stream and riverbanks to prevent encroachment or damage to the wetlands and the sensitive floodplain area.

“Overall, the terrain across the bore path is relatively flat except for a drop in elevation of approximately 6 feet within the stream banks and river,” says Hoge. “The entire area within a quarter mile of the bore was also within the floodplain of the river.”

Some of the challenges in completing this bore included maintaining the proper alignment within a limited utility corridor across the stream and river. In addition, the ground conditions varied between a loose gravel and cobble material to sand lenses and back to cemented cobble.

The bore began on the creek side with a setback of 150 feet to get to the desired depth of 27 feet below the river bottom and ended up on the river side 100 feet from the bank.

Earth Energy used its Vermeer D100X120 Navigator horizontal directional drill for this project-the newest addition to its fleet of six Vermeer drill rigs. The unit produces 100,000 pounds of pullback force and was fitted with a 6.5-inch single-roller-type cone drill head for the pilot bore.

“The pilot was pretty difficult,” says Burke Williams, operations manager for Earth Energy. “Due to the cobble, it was a struggle just to keep our pitches within reason for the diameter pipe we were installing. Once we got into the more solid formation, the bore went smoothly until we exited and again we had trouble keeping our pitch in the loose material.”

To make matters worse, the pilot bore had to be completed with an arc to avoid pilings from a future bridge that was to be installed parallel to the bore path.

Once the pilot bore was completed Earth Energy utilized a series of roller cone-rock reamers to pre-ream the borehole to a 36-inch diameter before installing the 24-inch HDPE pipe.

“We piggybacked the reamers,” says Hoge. “Once we completed a backream, we would use that same reamer to lead a larger-diameter reamer through the borehole. The piggyback procedure provided us with some stability inside the borehole, considering the ground conditions.”

With each 6-inch increase in borehole size, additional challenges were created in maintaining the proper mud mixture to remove the drill cuttings and prevent the borehole from collapsing. Earth Energy constantly adjusted the bentonite mud mixture to maintain the borehole. The loose unconsolidated cobble material near the surface was the most difficult to maintain.

The 24-inch HDPE waterline was staged on the exit side of the bore, and United Pipe, also of Boise, used a fusion machine to fuse the 50-foot segments. Earth Energy used a 32-inch cobble reamer to pull the 640 feet of pipe into place.

“The pullback was a piece of cake,” says Williams. “During the pullback, our pressure never exceeded 60,000 pounds per square inch, considering we were pulling more than 53,000 pounds of pipe into place. The total project from preplanning to completion took 42 working days.”

Planning Tools Invaluable
One of the advantages of using Vermeer equipment is the availability of the Vermeer Bore Pilot and Atlas Bore Planner software to design the directional bore.

“We deal with some pretty challenging bores and our planning software is a huge asset in our company,” says Williams. “Seven or eight years ago, we had to make our bore plans using hand levels and tape measures, creating the bore path by hand. It required considerable time, but with lasers and our Atlas Bore Planner software from Vermeer, it’s much easier and more efficient to map the topography and design the bore.”

According to Hoge, the initial step in utilizing the bore software was to determine which directional drill would be used on the bore. Once the drill size is determined, a topographic surface is built with the software, and the desired depths along the proposed route are input into the software program.

“The software designs the bore profile based on the allowable bend radius of the drill stem being used,” says Williams. “The computer will warn the user if the desired depths along the bore change too quickly for the drill stem in use. Additional restraints can be input into the computer to limit the bend radius of the drill stem and smooth or lengthen the arc of the bore to the desired final profile.”

Once the bore was completed, the actual as-built depths were input into the software and a comparison showing design versus the actual was graphically shown.

Earth Energy documents every bore they complete, whether it’s a 30- or 1,000-foot (9.1- to 304.8-m) bore, using a combination of the planning software and bore logs. Many times the company has been hired to go back and complete another bore at the same area.

“The bore logs and planning files are a great help in determining where we put the previous bore, what utilities we encountered in the first bore, where existing utilities are and what depth we bored,” says Williams. “The information is great to share with a customer, and it helps us estimate the cost of the project.”

Earth Energy tracks the depth of every rod and sometimes every half-rod. The crew follows along the bore plan profile to track any variances. In the end, an as-built is created and compared with the design.

“The software takes the guesswork out of the planning process,” says Williams. “If we try to design a bore too short and too steep for a particular drill, the software will flag the problem and assist us in correcting the situation.”

This project was one of Earth Energy’s more difficult, due to the size of the pipe, the sensitive nature of the waterways, and the variable conditions of the material to be bored. Earth Energy has completed much longer bores in cobble and solid rock, though the product size was typically less than 16 inches in diameter.

“We knew with proper planning and the right equipment we could complete the job and there really weren’t any surprises along the way,” say Hoge. “I think that speaks highly of our employees-they take pride in what we do.”

No matter what the ground or topography throws at Hoge and his team, they always seem to find a way to overcome the challenge.
About the Author

Greg Ehm

Greg Ehm is an account manager with Two Rivers Marketing in Des Moines, IA.

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