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Part 2 of our series on underground construction reports on the tools and techniques available and gives some real examples of how problems have been solved. By Paul Hull
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The contractor is ready to start trenching or drilling. The crew knows where the cuts or bores must be made. They know what obstacles, if any, are en route. They have taken every precaution to ensure a project safe for surrounding structures, bystanders (you know you’ll always have them!), and themselves. Experienced contractors know that it is unlikely that one trencher will be perfect for the entire underground construction project. If all the ground were earth without rocks or water and all the required trenches were the same depth and width, one machine could do everything. Even in the same community, there will be different ground conditions-places where rocks seem to prevail and other areas where the soil is sandy or frequently soaked with groundwater. Much of today’s trenching, however, will go across fields or beside roads in ground that presents little challenge to the sharp blades or teeth of the machines. "One of the forgotten considerations is the product being installed," notes contractor Sean Wootan. "If it is too rigid to go easily from a reel into the ground, it will demand trenches wider than its own diameter to allow for easy installation. When several cables or pipes are packaged together to make a multiple underground product, that is when it might become too heavy and rigid to handle in the same way as a single cable or pipe." Today’s trenchers, however, can handle widths that will accommodate most products. The choice between open-cut trenching (with trenchers or plows) and trenchless methods (with directional drills) is simple enough. Contractors nationwide agree that if there are no obstacles underground, no existing utility cables or pipe to worry about, no streets to tear up or highways to disrupt, then open-cut trenching is probably the answer. A combination of trenching and trenchless technologies is common for underground construction. Trenchers do the underground digging for telecommunication cable between communities. They work faster and more efficiently than excavators for these applications. A point in favor of trenchers is that they can cut neat trenches across streets, and these narrow trenches require little reconstruction. Before assuming that all street crossings must be trenchless, consider the cost of cutting the required trench with an appropriate trencher. Fortunately for contractors, several leading manufacturers of trenching equipment are also leaders in trenchless products-companies such as Vermeer, Ditch Witch, and Case - so don’t be shy about asking their advice. Trench Size Is Rarely a Problem
Trencher sizes vary from those that the operator walks behind (similar to running a lawn mower) to enormous machines that can cut their way through rock for large-diameter pipe or multiple cables. Vermeer Manufacturing (Pella, IA) has one of the most extensive ranges of trenchers, and it can show us what is available to contractors with cable and pipe installation projects. The three walk-behind trenchers range from 11 to 20 hp, 850 to 1,460 lb., and 0- to 48-in. digging depths. The digging width of walk-behind trenchers is usually in the 3.5- to 10-in. range. Utility trenchers are bigger. Vermeer features seven of these, with weights from 4,000 to 8,470 lb., horsepower from 43.5 to 116 hp, digging depths from 0 to 72 in., and digging widths from 5 to 18 in. Just introduced is the RT700/850 TerraFire, a fully hydrostatic utility trencher for midsize trenching needs, with a choice of 70 or 85 hp. The operator console rotates 90° , and standard rear-steering axles (including coordinated steering) handle different ground conditions. Utility trenchers can have vibratory plow attachments, but self-contained vibratory plows are also available. Vermeer offers three, with weights ranging from 8,700 to 29,300 lb. and plow cover depths from 24 to 60 in. These plows can also have reel carriers. A single reel carrier weighs about 3,000 lb., and a dual reel carrier weighs 7,500 lb. The practical combination of vibratory plow and reel carrier has proven most successful worldwide. The Vermeer T555 is a rockwheel trencher weighing 27,800 lb. with a cutting depth of 0-36 in. and a cutting width of 4 or 6 in. A TEC 2000 controls this heavyweight machine. For track trenchers, there are 13 in Vermeer’s range, with 79-700 hp, 8,700-180,000 lb., and up to 21-ft. digging depths. The digging widths vary from 6-12 in. for the smallest model to 36-56 in. for the largest. Based on the parameters of this sample Vermeer range, it shouldn’t be tough to find a trencher to meet most specifications. For S&N Communications, headquartered in Walkertown, SC, telecommunications system construction is its primary business. It has 25 Ditch Witch 5700 vibratory plows equipped with backhoes and Roto Witch nondirectional drilling tools that can be quickly mounted on a machine’s backfill blade. Despite the increased use of fiber cable for long-distance telephone routes, S&N still installs miles of copper cable for residences and businesses. The plows install the cable to depths of 24 in. "The Ditch Witch machines are excellent for our needs," remarks B. Wayne Newkirk, CEO. "Having a backhoe and drilling attachment on each plow unit eliminates the need to bring other equipment to job sites." In addition, S&N has four Ditch Witch 8020 vibratory plows, larger machines with cable reels mounted on the front. Ditch Witch also offers a range of smaller trenchers suitable for work at residential, commercial, and industrial sites. Combining the company’s trenching and trenchless equipment is a frequent solution to municipal problems. For installing a new lighting system for several miles along the median of a highway, the contractor used a JT1720 directional boring unit for some of the work, but a Ditch Witch 5110 trencher completed 90% of the job. Matching the Trencher to the Soil Conditions Mastenbroek (Boston, England) offers rock trenchers with horsepower from 119 to 925, weights from 15,215 to almost 220,500 lb., trench depths from 0 to 19.6 ft., and widths from 1.2 to 8.2 ft. You can put some large product or multiple lines in trenches of that width. The company enjoys worldwide success with projects for cable installation, highway trenches, sewerage and water pipes, gas pipelines, and even undersea work. "Each project is different," points out Sales Manager Peter Maskell. "We offer a range of nine rock trenchers, and each can be tailored to a contractor’s individual requirements. With the automatic creep load control system, the trencher’s speed is constantly and automatically adjusted to ground conditions, while the oscillating tracks on the larger models improve stability and allow the contractor to trench cross-country on uneven terrain." Trencor (Grapevine, TX) makes and markets chain trenchers, wheel trenchers, and rock saws. In a range of 11 chain trenchers, the engine output varies from 185 to 1,500 hp, the maximum cutting depth ranges from 6 to 35 ft., and the cutting width range from 10/18 to 48/96 in. Trencor’s wheel trenchers have proven successful for utility and pipeline work. At one project (for 87,000 ft. of pipe), the ground was hard sandstone with an abrasive factor between 90% and 95%. Once broken, the rock becomes chips and can be rubbed between your fingers to become sand, but the first problem is breaking it into those chips. The contractor used a Trencor 1260HD. "It worked out well for us," states contractor Bill Mayse. "We cut about 16 inches wide and 48 inches deep. The tooth wear has been lower than we thought it would be, but we used special teeth developed by Sandvik Rock Tools. Production varies, but we manage to achieve about 275 to 300 feet per day." That project was not all cross-country trenching but right down the middle of a narrow, winding residential street for some distance. "As an alternative to blasting, the residents loved it," adds Mayse. Rock saws frequently work in rock or under existing pavements. A project where you can see all the types of trenching and trenchless equipment in operation is the 16,000-mi. installation for Level 3 Communications of the Internet Protocol technology - based telecommunications network. Kiewit Network Services Company, based in Golden, CO, is the primary contractor. "While trenching and plowing methods are appropriate to some types of soil, rock saws are used when there is a heavy concentration of rock," observes Karen Morales of Kiewit. For one long section, the company used Tesmec TRS-1100 rock saws. The average trench depth was 42 in. and average width was 12 in. (for placing from 12 to 20 conduits). The big Tesmec TRS-1100 uses 350 hp. Hydrostatic rock saw drives use two pumps and motors to transmit maximum power to the carbide-tipped cutters of the trenching wheel. Among smaller models from other manufacturers, Burkeen Manufacturing Company (Olive Branch, MS) has recently upgraded the B-30B vibratory plow, giving it more horsepower and Dana limited slip axles. "Not all sites are dry," states a spokesperson for Burkeen. "The big foot flotation tires of the B-30B give it good stability and traction in soggy or muddy conditions." The same company also manufactures riding trenchers. Case Corporation (Racine, WA) manufactures a range of eight trenchers, with horsepower from 13 to 77, operating weights from 720 to 12,700 lb., and maximum digging depths of 36 to 84 in. The depth control is hydraulic on Parsons Trenchers and Cable Plows. Smaller units, suitable for housing developments, with some walk-behind and others riding-style, offer digging widths from 4 to 18 in. and digging depths from 0 to 108 in. Mounted on a truck, the Kukla Unimog can cut as wide as 42 in. and as deep as 72 in. Its 230 hp comes from a Cummins engine, and its maximum torque is 760 Newton meters (Nm). Advances in Trenchless Technologies A new hot-water heating system for two apartment buildings demonstrated the versatility of trenchless technologies, and a large storage building located in the center of the residential site would serve as the power station. The water would be heated there and distributed to each apartment through a main supply line. Contractor Spiekermann won the contract to install 10 private connections. He opted for a Grundodrill 10 S from Tracto-Technik (TT Technologies). "In addition to connections, we had to perform two road crossings [each over 40 yards] for the main conduit to the power station," Spiekermann points out. The pipe used (known as LR-Pex) works for temperatures up to 200° F. There would be four ducts or carrier pipes to be pulled: two at 4 in. for supply and tank lines to the central heating station, another at 4 in. for the hot-water supply, and one 3-in. circulation pipe and one 4-in. carrier pipe. The Spiekermann crew says the drilling length of 70 ft. did not worry them, but trying to reach a basement of brick construction did. Access was only 47 in. long, 59 in. wide, and 51 in. deep. Any method other than directional drilling would have faced enormous difficulties in such a tight corner, especially with unpredictable soil conditions where, for example, sandy soils suddenly turned into compacted gravel with little sand or soil particles. In such conditions, it’s difficult to stabilize the bore tunnel. The operators had to know all about bentonite viscosity and flow in order to keep the bore tunnel from collapsing after the pilot bore. Spiekermann used a Grundodrill 10 S with an integrated percussive hammer for this job, with an RD 385 (from Radiodetection) for locating and tracking. The scheduled installation depth was at 11.5 ft. "We reached this pilot bore depth by entering the drill stems with an inclination of 35%, then turning to 20% after the third drill stem, to 10% after the fifth, and 0% after the seventh drill stem," explains the contractor. After the pilot bore, the Grundodrill operators decided to run a pre-reaming step, using a backreamer of 7.5 in., to give the bentonite time to stabilize the bore and avoid the collapse of the bore hole in the sandy or sandy, gravelly soil. During the final backreaming step, they pulled in a reamer of just over 11 in. Because of their mechanical resistance, long-distance heating pipes cannot be towed in directly by using polyethylene pipe pullers, so the contractor used cable sockets, secured with a bolt and fastened to the backreamer with a shackle. The time required to pull the multiduct pipes varied from 10 to 20 minutes, depending on the soil it went through. The customer favored the speed and cost of the directional drilling. The whole project (including the auxiliary work and the road crossings) took seven days, making it more than twice as fast as a previous attempt with different equipment.
The increase in demand for directional drilling work for pipelines and utility installations underground is the result of several reasons-environmental concern being one of the most influential. There is a measurement of quality known as ISO 14001 -demanded by law in Europe for many projects-which seeks to protect our environment for present and future generations. For underground construction, it says that drilling around or under tree roots and plants should be planned instead of destroying the roots and, consequently, the beauty above the surface. Directional drilling does that and saves energy too. For a typical street crossing using open-cut methods, about 212 ft.3 of spoil would be moved. A directional drill launched from a pit would require 30 times less! Ditch Witch (Perry, OK) emphasizes that its Jet Trac System is a complete system, not just a directional boring machine. The JT1720 (a compact model in the range weighing 10,500 lb.) has an 85-hp diesel engine, and the hydraulics deliver 17,000 lb. of pullback. "An interesting aspect of this machine is that the rotation, drilling fluid, and thrust/pullback functions can all be working at the same time without one taking power away from another," points out Jeri Kannenwischer for the manufacturer. "This means that the boring unit can handle multiple conduits up to 500 feet." For operation, setup is fast with a ground drive controller allowing one person to load and unload the boring unit. Adjustment of the boring angle is hydraulic. The design of the JT1720 reflects features requested by operators, with a pivoting operator’s station to provide a good view of the work in progress and a single-handle control to run both thrust/pullback and rotation (with variable speed for all functions). The Ditch Witch system automatically lubricates the pipe threads as part of the loading and unloading process, and there is also an onboard drilling fluid system. "In consideration of the people affected by the boring project, the rubber tracks of this model are kind to both turf and concrete," states operator Doug Jordan at a residential site. "The noise levels have been kept to an acceptable range for both me and the neighbors." In addition, the tools-the right bits for the soil conditions, backreamers, swivels, pulling tabs, and drill pipe itself-are of paramount importance in every underground bore.
Contractors who use trucks always want more horsepower and more capacity. The operators of underground boring equipment demand similar results. The power of directional boring machines (and the diameters and lengths of the bores they make) have steadily increased. An interesting system from Vermeer’s large range is the RockFire AS6 rock drilling system, which incorporates a Vermeer Navigator horizontal directional drill with a pneumatic down-hole hammer, an air compressor, and a foaming agent to clean the cuttings out of the bore path. Not all drilling goes through soft soils. The RockFire system works with medium-size horizontal drills for short- to medium-length bores. It can cut a bore path with a diameter of 6 in. and allows many products to be pulled into place without requiring extra backreaming. An essential part of the system, the foam solution (developed by Baroid Drilling Fluids) is environmentally friendly and helps to remove rock cuttings during the drilling process. A recent addition to the Vermeer line is the D7x11A, a compact machine most suitable for house-to-curb projects, with high power in a small footprint. It offers 1,505 Nm of torque and 7,800 lb. of pullback. Most manufacturers of directional drilling equipment can supply everything needed for your projects. Tulsa Trenchless (Kiefer, OK) purchased the mini horizontal and drilling division of Ingersoll-Rand a couple of years ago. It offers not only the drilling equipment but also mud systems, locating equipment, trailers for transportation from site to site, drill heads, drill rods, swivels, buts, and reamers. The company features three models with thrust and pullback from 7,200 to 38,500 lb. Tulsa Rig Iron is the big brother of Tulsa Trenchless, offering horizontal directional drilling equipment with thrust/pullbacks from 50,000 to 250,000 lb. "We have built custom equipment, including one huge machine for the Chinese government," says Ray Clayton for the company. "It had a static pullback rating of more than 750,000 pounds." The DD-660 from American Augers of West Salem, OH (an Astec Industries company), offers 330 tons of pullback. The high-rotary torque (120,000 Nm) turns large reamers in long bores, while the rack-and-pinion design gives an equal force for both thrust and pullback. Along with its broad range of drills, American Augers offers rock and dirt bits, tri-cones, sonde housings, swivels, cutters, hole openers, and reamers. On the DD-1, a much smaller rig from this manufacturer, work lights are standard equipment (because nobody can guarantee that all trenchless work is done in the daylight). This is a self-contained model and moves on rubber tracks that do little damage to pavement or grassy surfaces. Many general contractors (for whom trenchless work is only an occasional assignment) already own skid-steer loaders. Among several horizontal directional drills from Case Corporation are the 150CM and 300CM, and these can be mounted easily on skid-steer loaders, with only five minutes required for setup or takedown. Case also offers two truck-mounted models that can be driven on and off the site with no additional trailer required. For more demanding applications, Case has introduced the 6010 Turbo and 6030 Turbo horizontal directional drills, delivering 51,155 and 133,447 N of thrust and pullback, respectively. The new models combine the Case Duplex chain drive design and high-efficiency hydrostatic motors. These machines have an automatic rod-loading system as standard equipment. To handle the larger-diameter pipe used in utilities, McLaughlin Manufacturing (Greenville, SC) developed the McL-30/36B and McL-36/42B auger boring machines, the largest in their range. The first model handles pipe with diameters up to 36 in., and the McL-36/42B copes with bores from 12 to 42 in. It develops more than 38,221 ft./ lb. of auger torque in first gear, and triple hydraulic rams produce a forward thrust of 400,000 lb. Both of these auger boring systems include a four-speed transmission with reverse, a patented Operator Presence Control hydraulic clutch to improve safety and reduce train wear, dual planetary reduction, and a pistol-grip lever that controls both auger rotation and forward thrust. Paul Hull is a frequent contributor to Grading & Excavation Contractor. Click here to read part 1 of our series on underground construction.
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