ASCE Manual of Practice No. 118 For Belowground Pipeline Networks For Utility Cables

U-Tech: Underground Technology Cutting Edge Technical Information for Utility Construction and Rehabilitation
By Dr. Lawrence M. Slavin, Dr. Oleh Kinash, Dr. Mohammad Najafi | January 2010 Vol. 65 No. 1
Figure 2 Typical Underground Conduit Construction (Courtesy of Underground Devices, Inc.)

Direct-buried systems
In contrast to underground conduit systems, direct-buried plant (mode three) represents a relatively low cost method for placing individual cables belowground between any desired terminations, but loses flexibility with respect to future additions or replacements. (Figure 3 illustrates typical direct-buried construction.) Indeed, the inherent lack of such upgradeability has been a primary factor in inhibiting the desired widespread deployment of new wireline telecommunications technologies, based upon the use of fiber-optic cables, in established areas and communities with buried facilities. Conversely, existing communities served by aerial distribution plant (mode one) have been ready candidates for such upgrades. Similarly, energy-hungry consumers and industries continue to push the limit of existing power lines which need to be replaced or supplemented. Thus, in addition to the relatively low cost to install and maintain aerial facilities, flexibility represents another reason for the continuing deployment of aerial lines.

The current trends for buried construction across much of the country introduce potentially serious problems when upgrades and maintenance are inevitably required in the future. In such cases, digging in established areas is typically required, often accompanied by damage to public and private property, including roads, and associated traffic problems. Furthermore, there are safety problems corresponding to digging in an area with existing utilities (electric power, gas). Even when proper procedures (One-Call notification, identification, utility location, manual exposure) are followed, accidents can occur, resulting in property damage and personal injury, possibly death. The use of “trenchless technology,” including horizontal directional drilling (HDD), following proper procedures, does reduce the degree and likelihood of such problems, but does not eliminate them, and typically has a significant cost penalty. Thus, while current trends in the widespread use of buried construction are desirable, there is an urgent need to modify present construction practices to avoid unfortunate future problems, including significant safety issues.

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Figure 3 Typical Direct-Buried Construction

Such innovative methods have been developed under the sponsorship of the U.S. Department of Transportation, for which detailed information is provided in the manual, as discussed below.
There are several general methods currently available for the “direct-burial” of cables, as well as individual relatively small ducts (e.g., one to 2-inches):