Utility Contractor

MAY-JUN 2018

As the official magazine of NUCA, Utility Contractor presents the latest information affecting every aspect of the utility construction industry, including technological advancements, safety issues, legislative developments and instructional advice.

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May/June 2018 | Utility Contractor 35 • Environmental - No dewatering of the soil is required there- fore no water treatment and disposal issues arise; Storm water mitigation is limited to manhole locations; Equipment pollution is limited to off haul of excavation at manhole/shaft locations; Environmental disturbance is eliminated by tunneling under sensitive areas. • Design Requirements - Imported gravel backfill is limited to manhole locations; Surface restoration is eliminated and lim- ited to manhole locations; Existing utility damage from expo- sure during excavation is eliminated by tunneling under or over the utility. • Safety - Trenchless methods are inherently safe – no trench shoring is required; Shoring is required only at manhole/shaft locations; Safety exposure is limited as crew sizes are commonly 4-6 persons; The presence of water in soils is not a safety issue – water is a benefit providing lubrication and tunnel face stability. The introduction of new technologies to the U.S. market have made trenchless installations much more competitive. Until re- cently, trenchless technologies for gravity sewers such as pilot tube, slurry and auger microtunneling methods have been more expensive than open-cut methods. The high cost of shafts has been a major factor with shafts often costing more than the tun- neling itself. Recently, rapid shaft technology has been introduced in the United States, reducing the cost of shafts substantially. The in- troduction of pilot tube and auger microtunneling equipment to install PVC and ADS pipes as well as all other sewer pipe types also reduces the cost of trenchless installations. Pilot tube and auger microtunneling systems in the 8- to 30-in. pipe sizes now have a much wider range of soil types where installation is possible. Where it is impractical to install pipe in fluid soils and hard rock conditions by open-cut, it is well within the capabilities of trenchless methods. Current pilot tube and auger microtunnel- ing systems have been reported to have installed pipe in hard rock of up to 22,000 psi unconfined compressive strength. It is also common to install pipe in very fluid soils with Manning's n-values as low as 1. The comparison of open cut and trenchless methods for sewer installation confirms the cost, environmental and safety advantages of the trenchless methods, specifically for smaller diameter pipe installations. The cost reduction of trenchless technologies and the cost increases for open cut methods are expected to continue. The advantages of new and continued improvements in trenchless technology are resulting in less risk, less cost and more profit for contractors. Mike Ellis is owner of Trenchless Equipment Co. (TEC) based in Orem, Utah. For information visit trenchless.net.

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