Directional boring conquers Cowskin Creek.
To date, horizontal directional boring has had little impact in the area of public works. But the benefits of directional drilling are beginning to interest public works officials; some cities have acquired directional equipment.
The availability of restrained joint PVC pipe meeting standards for municipal water systems makes directional boring a viable option for many water projects. Restrained joint pipe allows directional boring installations of water and fire service lines in situations where excavating should be avoided and when directional boring is the most cost-effective method of construction, says Marc Messner, president of Horizontal Drilling Technologies, Oklahoma City, Oklahoma and Wichita, Kansas. Directional boring machines can place pipe under paved surfaces; streams, rivers, and lakes, and in areas where it is important not to disturb the environment. Extensive excavations and costly, time-consuming restoration are eliminated.
Restrained joint pipe can be installed by directional boring, because pipe sections are connected using couplings that lock tightly and will not pull apart when the pipe is pulled into place by the boring machine, says Roger Staley, territory manager for Certainteed Pipe and Plastics Group (Valley Forge, Pennsylvania). Certainteed Certa-Lok[TM] C-900/RJ pipe presently is the only restrained joint PVC pipe meeting AWWA C-900 standards for municipal water pipe, says Staley. It has U.L. and F.M. listings for fire service lines.
A recent project in Wichita, Kansas illustrates the process and documents its benefits in one specific situation. An expansion of the city's water distribution system included placement of 12-in. C-900 DR-18 PVC water main beneath Cowskin Creek. Width at the point of crossing was approximately 50 ft.
"The City of Wichita had been considering new construction techniques," says Staley, "and decided to use the opportunity to try directional boring to cross the stream.
This segment initially was designed for open cutting, but was altered to allow trenchless installation to limit damage to the creek banks and surrounding areas."
The primary contractor for the project, Wildcat Construction Company (Wichita), subcontracted the bore to Horizontal Drilling Technologies (HDT). To eliminate damage to creek banks, 400 ft of pipe was installed by directional boring.
The first step, says Messner, was to make a pilot bore under the creek. Using a Ditch Witch[R] JT 3510 directional boring system (The Charles Machine Works, Inc., Perry, Oklahoma), the HDT crew launched the 5-in. diameter pilot bore from one side of the creek, guiding it downward and leveling the path so that the bore would be at least 10 ft under the creek's bottom. Because of land configuration, average bore depth was 22 ft. Soil was clay to depths of 15 ft. Under the clay was fine- to medium-grain silty sands to the maximum bore depth.
As the bore proceeded, sections of drill pipe were added. Progress of the bore was monitored from the surface with an electronic tracker, which receives radio signals from a beacon transmitter mounted in the bore head. The hand-held tracker provides location of the bore head, its depth, percent of grade, and information for steering the path of the bore. The shallow depth of the creek permitted the operator of the tracker to wade across it, taking readings as he held the instrument above the level of the water.
After the pilot bore was completed, the hole was enlarged with a series of passes using a 14-in. backreamer followed by 20-in. cutting and compaction reamers. 20-ft sections of pipe were prepared for installation by being coupled with restrained joints. Precision-machined grooves of pipe and couplers are aligned, and a nylon spline is inserted to provide a fully circumferential restrained joint locking pipe and coupling together. A flexible o-ring in the coupling provides a hydraulic pressure seal. If necessary, the joint can be disassembled later during system changes and extensions.
After the hole was enlarged, pipe then was attached to the drill string and pulled back through the bore hole. As the PVC pipe was brought back toward the drill frame, sections of drill pipe were removed.
Drilling Fluid Lubricates Pipe
The JT3510 boring system uses drilling fluid while making the pilot bore and during pull back. During pipe installation, fluid lubricates the pipe, reducing friction as it is brought through the hole and maintains the integrity of the walls of the bore hole, reducing the chance of its walls caving in around the pipe.
"The restrained joint system makes it possible to install gasketed water pipe by directional boring," says Messner. "PVC water pipe connected with ordinary 'shove joints' would come apart during pullback."
The speed with which restrained joints can be made is an important factor, says Messner. "Certa-Lok restrained joints are completed about as fast as we can remove joints of drill stem during the pullback," he says.
Connections can be made as the pullback progresses, eliminating the need to join all sections of pipe prior to installation. On many job sites, there is insufficient space to lay out several hundred feet of pipe.
"Once you start pulling in pipe, you can't stop a pullback for extended periods of time," says Messner. "If you have to wait 45 minutes for glue to set or to fuse polyethylene pipe every time a connection is made, fluid flow will be lost and the walls of the hole could collapse around the pipe, causing it to become stuck, or the increased friction could result in pipe failure."
Messner says the JT3510 system is ideally suited for water system work. "It is compact enough to work in confined areas," he says, "and has the power to back-ream and pull in large-diameter water pipe."
Power of directional boring equipment is stated in thrust and pullback, the relationship of torque and speed at the downhole tools, and downhole horsepower. The JT3520 develops 26,000 lb of thrust (for boring) and 35,000 lb of pullback. Maximum torque is 2,670 ft lb with spindle speeds of up to 330 rpm in high range. An exclusive boring monitor automatically adjusts carriage speed during boring and pullback.
The self-propelled drill frame is mounted on rubber tracks. Power source and hydraulic and fluid systems are on a trailer that can be positioned in the most convenient location as far as 200 ft from the drill frame.
Horizontal directional boring for utility construction is a relatively new development. The first utility units were introduced in the late 1980s, and their wide acceptance for natural gas, power, and telecommunications work has occurred in the last three to four years.
Although interest in directional boring is increasing, Messner and Staley agree that many public works officials are not aware that directional boring is applicable to public works projects, believing the equipment is suitable only for installing cable and small-diameter pipe.
Directional boring is particularly appropriate for installing replacement water service lines in developed neighborhoods, Messner says. Streets, sidewalks, and project driveways do not have to be cut, and landscaped lawns are not disturbed. Pipe can be installed beneath existing buried utilities and underground sprinkler systems. Small boring units have been developed for service work. They can go through a 36-in. yard gate.
Certa-Lok restrained joint C-900/RJ PVC pipe has been available since 1994, says Staley, but its suitability for installation with directional boring equipment only recently has been recognized and documented.
Directional boring can install restrained joint water lines in urban and developed areas, at industrial complexes, in parks and recreation areas, under streets and freeways, under rivers and lakes, in areas where terrain prohibits the use of excavating equipment, and in environmental-sensitive areas.
"Wichita and other cities now consider directional boring when replacing old water mains or extending lines into new developments," says Staley. "Compared to open-trench installations, finished costs are very competitive."
Reduced time for construction and the elimination of restoration time can mean significant savings. "In Wichita," says Messner, "if the creek crossing had been made by excavation, the creek would have had to be dammed and the banks shored. This segment of the job could have taken weeks to complete would have cost twice as much. Typically it takes three or four days to open cut a 500-ft section of water main in a residential area. We can do it by boring in a day."
Messner and Staley believe the public works market holds tremendous potential for directional boring. "The knowledge that the equipment and product are available and that successful installations are being made will encourage more cities to take advantage of the benefits of directional boring," says Staley.
About the Contractor ...
Horizontal Drilling Technologies (HDT) is a company whose name exactly describes the services it provides. Founded in 1993, HDT has offices in Oklahoma City, Oklahoma and Wichita, Kansas and operates nationally.
"Horizontal Drilling Technologies," says president Marc Messner, "provides economical, cost-effective horizontal directional boring solutions for the installation of all types of pipe and tele- communications and power cable."
From basic installations to complex projects, HDT offers a full-service approach for every phase of a job, including manholes, vaults, and concrete structures necessary to compliment other portions of a job.
HDT's five directional boring crews are experienced in routine cable and piping installations through back yard easements and parking lots, river and lake crossings, and installations beneath highways, freeways, and railroad tracks. HDT is one of only a few contractors in the U.S. using directional boring equipment to install horizontal remediation wells and manifold piping for environmental dean up projects.
Directional boring is not been widely used to install pipe for water systems. "One reason public works officials have not considered directional drilling methods before," says Messner, "is the impression that the directional machines used for utility work "are only capable of putting in cable and small-diameter pipe. Actually, compact directional boring equipment can handle much of the pipe used for water distribution systems, and it is ideal for putting in new service lines in established neighborhoods. Small-diameter pilot bores are enlarged by backreaming to accommodate larger diameter water pipe."
Messner believes a growing number of municipal officials will begin looking closely at the benefits this method of construction offers. "Reduced restoration costs alone often make directional boring the best option in many situations. In addition to cost savings, reduced excavation has a very positive public relations value. People appreciate it when work can be done without tearing up streets or destroying their yards."
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|Title Annotation:||water distribution system of Wichita, KS|
|Date:||Feb 1, 1997|
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