September 2011, Vol. 66 No. 9
Features
Missouri Rock, Ozark Mountains Big Challenge To Gas Line Installation
Challenging underground projects attract interest — contractors who complete difficult jobs like to talk about them and manufacturers of equipment used are quick to tout the capabilities of their products.
Summit Utilities Management Services LLC, Littleton, CO, recently completed a 49-mile-long natural gas transmission line through Missouri’s rugged Ozark Mountains that certainly qualifies as a major challenge worth talking about. In fact, Bret Brown, Summit’s business development and construction manager, called the project the most difficult he’s ever worked on.
The route for the 8-inch steel pipeline was from Aurora to Branson, MO, a popular family vacation center that is home to Silver Dollar City, more than 50 live performance centers, a dozen championship golf courses and a host of other attractions.
Summit was the project manager and the project owner was Southern Missouri Gas.
“This project had the hardest rock we’ve ever encountered, from 16,000 to 22,000 psi,” said Brown. “In addition to the hard rock, work was made more difficult by the terrain’s ups and downs, steep side slopes and drop offs. I’ve had pipe projects in rock in the Rocky Mountains at elevations from 9,500 to 12,000 feet. This one was much more difficult than the Rockies.”
The majority of the pipe was installed by open-cut construction, using six 440-horsepower chain trenchers. Trench width was 24-inches with depths averaging six feet.
Crossings
Horizontal directional drilling also played an important role on the project. Brown said HDD was used throughout the project, primarily for road crossings and going under streams and rivers.
“There were 40 bores on the route ranging from 80 to more than 500 feet with the average length 150 feet,” said Brown. “The longest was 1,200 feet under a river.”
Rock conditions made HDD segments challenging. The rigs used by Summit included a Ditch Witch JT100 and JT4020, both All Terrain (AT) models for drilling in rock.
The JT100 is the largest Ditch Witch drill unit powered by a 268-horsepower diesel engine. It produces 100,000 pounds of pullback, 12,000 foot pounds of torque and a maximum spindle speed of 270 rpm.
The JT4020 produces 40,000 pounds of pullback, 5,000 foot pounds spindle torque and spindle speeds to 250 rpm.
The dual-pipe All Terrain drilling system is designed to drill through hard rock without the use of a mud motor.
At the same time the transmission line project was under way, Summit was installing the gas distribution system to bring natural gas service to homes and businesses in the city of Branson. The system includes installation of 60 miles of HDPE pipe in diameters of 6, 4, and 2 inches. Subsurface conditions in Branson also are rocky.
City boring
“Almost of the pipe in the city is being installed by horizontal directional drilling,” said Brown. “The right of way is so narrow, there already are many buried utilities, traffic is heavy, and much of the area where pipe goes is landscaped. There really is no other way to do the job.”
Average length of bores for the mains is from 450 to 500 feet at an average depth of 36 inches. Residential services are 3/4-inch in diameter and are installed 24 inches deep. Lengths vary with each home. Commercial service lines are two-inches in diameter to provide needed capacity, and some are as long as 1,000 feet. Commercial services are 36-inches deep.
Included in the 13 HDD units working in Branson are Ditch Witch JT3020 and JT4020 All Terrain models.
“The capabilities of these machines has proved to be an important factor in completing this project,” said Brown. “Going into the job we projected each drill unit could average 300 feet per day. We are averaging 700 feet per day with these machines.”
Although relatively compact in size, the JT3020 AT develops 30,000 pounds of thrust, 4,000 foot pounds of torque, and spindle speeds to 225 rpm.
The mechanical dual-pipe system delivers maximum downhole horsepower and operates on low volumes of drilling fluid. The AT design employs an inner rod to drive a rock bit, and the outer pipe steers the downhole tool for drilling pilot holes and provides rotary torque for the hole opener during backreaming. In addition to rock drilling, All Terrain models are productive in almost all types of soils.
Also they used a Ditch Witch FX30 vacuum excavation system which is typically used for potholing and clean up of work sites. It is equipped with an 800-gallon spoil tank.
Summit Utilities Management Services specializes in constructing natural gas distribution systems to provide natural gas to residential and commercial customers.
Southern Missouri Natural Gas, Mountain Grove, MO, owns and operates over 400 miles of natural gas pipelines and is expanding its system to serve the communities of Houston, Branson, Hollister, Mountain Grove, Lebanon, West Plains and others.
FOR MORE INFO:
Summit Utilities, (800) 720-8193, www.summitutilitiesinc.com
Ditch Witch, (800) 654-6481, www.ditchwitch.com
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