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Protecting Our Global Environment |
Case Studies
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In October 1992 Environmental Crossings, Inc. (ECI) of Traverse City, MI, began a drilled crossing project for Connecticut Cable Construction & Maintenance, Inc. of Middlefield, CT. Project owner was Cox Greater Hartfort CATV. The project called for two directional crossings, one with a sharp lateral turn, but with both to terminate in a manhole location. The highway intersection crossing work was part of a larger 8000 foot fiber optics installation contract performed by Connecticut Cable Construction. ECI completed about 3800 feet of directionally installed conduit in which they pulled back 4 in. multi-cell pvc duct for the fiber optics cable. |
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ECI supplied two 30 foot drill-collars, a downhole jet-bit drilling assembly, and oilfield drillpipe that would also serve as the conduit when the drilling was completed. A drilling rig from Drilex Environmental Services was utilized to perform the drilling procedure. CBC-Welnav, Tustin, CA, supplied lateral navigation equipment, Accu-Tracker surface locator, and directional drilling engineers. |
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The scope of the project was to directionally drill two crossings via trenchless technology and leave a 5 in. O.D. conduit in place for fiber optic transmission cables. The crossings were to share the same exit point into a planned manhole. By using computer software developed by CBC-Welnay, ECI planned the directional crossing profiles. Profile #1 called for a basic approach: 1) Use a slant rig; 2) Directionally drill dow & horizontal; 3) Come up and out of the ground in a straight line from entry point. Profile #2, however, was a lot more innovative and optimistic. It required a grade change from 12 degrees to +10 degrees with a 130 degree lateral turn within 10000 lineal ft. of the drilled hold. The complexity of this project was in the drilling of profile #2. The jet-bit had to be navigated in a three dimensional plane. This type of project has only been approached by oilfield drilling, where no exits are involved and targets are much larger. Therefore this project was unique for two reasons: 1) 130 degree lateral turn; 2) accuracy of the drilled path to target. |
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Crossings: The first phase of the project began October 1st. and completed by October 3rd. The drilling operation under Highway 91 South was routine and all systems performed as expected. The drilled path was installed at a depth of 40 ft. The jet-bit exited on target and the drillpipe was left in place as a conduit for a total length of 519 ft. |
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On Oct. 4th. the drill rig was mobilized and moved to the second drill site. Profile #2 was reviewed. Practical application of drilling a 130 degree lateral turn in less than 1000 ft., began to cause both apprehension and enthusiasm. According to the profile, first few joints of drillpipe were actually drilled away from the target. The downhole jet-bit drilling assembly performed as predicted, and the curve began to take shape. The soft formation allowed for a fast penetration rate, but ECI kept the drilling speed and radius of curvature (dog-leg) in check, since profile #2 was approaching the bending limits of the drillpipe and the downhole drilling assembly. On Oct. 9th., the jet-bit exited on target 1000 ft. from the drill rig and joined up with the first phase crossing at the planned manhole site. The casing on both crossings was left in place, as a conduit for four polyethylene inner-ducts, which ECI was bundled and pulled back. |
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ECI planned two crossing project for Connecticut Cable without having any suitable alternatives. The right-of-way, entry, and exit points were pre-determined. The project design was complicated by the state's plan. The plan was to restore wet lands by lowering the site grade, which further limited the construction options. |
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Profile #2 crossing was a medium length lateral crossing, but the 130 degree lateral turn is believed to be a world record. With careful analysis of the physical properties, ECI approached the job and determined the drillpipe to be used. Doug Allman is ECI's vice president-engineering and project engineer for the Connecticut Cable crossing. He said, "They had verified the tensile strength of the pipe; they knew the radius bend that could be anticipated with the drillstem; and they considered the soil formations in which was being drilled." "There were plenty of nay-sayers. Even drilling professionals who stood on the site and said: It couldn't be done. But you will never finish, if you don't start something! ECI delivered the project and came in under budget," Allman said. Charles Ferrara President of Connecticut Cable Construction & Maintenance commented: " I was very amazed and very grateful for ECI's job performance! The alternatives would have been two to three times more expensive than the directional drilling." The original project design called for the site to be cleared and the cable to be trenched. State agencies rejected that idea, which led to the drilled crossing design. Ferrara mentioned that he had three different contractors look at the project design: One said it couldn't be done; Another doubted that it would be possible; The third was ECI, and they completed it as planned. The completion of the Connecticut project is a compliment to the parties involved. A major step forward in the new industry. Each successful lateral crossing breeds new interests, and the planning engineers are continuing to offer even greater challenges. - And the Two Became One - |
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WATER, SEWER, PETROLEUM, POWER, COMMUNICATIONS LINES
FIBER OPTIC BUNDLES, PNEUMATIC TRANSPORTATION TUBES |
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