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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
The objective of the manual, or guide, is to present a brief description of present and past practices for the placement of utility cables belowground, including conventional underground conduit systems and direct-buried methods, as well as more recent techniques in which individual pipes or ducts may be advantageously deployed in conjunction with “direct-buried” cables. Related design, construction and operational requirements and guidelines are also provided, as well as a brief description of various methods and technologies for placing cables into the conduits. In addition, specific design and implementation information is provided for a cost-effective, space efficient hybrid joint-use system for utility cables that provides many advantages relative to previous or existing methods of belowground construction.
The manual is divided into six main sections, consistent with the sequence in this article.
Underground conduit systems
The extensive conduit facilities of underground plant (mode two) are appropriate for limited applications, such as associated with the trunk or feeder portions of the traditional telecommunications network, due to the high cost of this method of construction. The construction of the conduit networks is material and labor-intensive, and requires significant manhole real estate, but does provide flexibility, including the capability to postpone installation of expensive trunk or feeder facilities (fiber-optic) until the need arises. Such underground conduit systems are also the only viable alternative in metropolitan or large urban areas where overhead lines and/or future digging are not an option. Figure 2 illustrates typical underground conduit construction.
Section 2 of MOP No. 118 provides a description of underground conduit systems including the basic components (conduits, structures and accessories) and design and construction requirements. Information is provided in the following categories:
Safety-Based Requirements (National Electrical Safety Code)
o Location and position;
o Excavation and backfill;
o Ducts and joints; and
o Manholes, handholes and vaults.
Design and Construction Guidelines
o Conduit sizing;
o Section lengths;
o Conduit type (PVC, HDPE); and
Operation and Maintenance
o Conduits (accessories); and
o Manholes (work rules).
o Cost (facilities, maintenance); and