ASCE MOP 118

Abstract

Underground pipes, or conduits, represent a routine means of installing and protecting cables, including telephone, cable television (CATV), and electric power supply lines. An array of such pipes, often encased in concrete, is typically part of a formal conduit network, including manholes placed at access points along the route, and is commonly used in urban areas and other locations for which the periodic placement of such cables is planned or anticipated. In contrast, the use of individual pipes or ducts placed in a trench, similar to direct-buried1 cables is less common, but has occasionally been used by individual utilities to provide a degree of upgrade capability not otherwise provided by conventional, low-cost, direct-buried construction methods. Such applications have not been used on a routine or coordinated basis among the utilities, although such utility companies may be sharing a single, <em>joint-use</em> trench. In the present context, joint-use refers to the sharing of aboveground or belowground facilities by several utilities or organizations using cables, such as electric power and communication (telephone or CATV) companies. <br>The objective of this book 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. Finally, specifi c design and implementation information is provided for a cost-effective, space effi cient hybrid jointuse system for utility cables that provides many advantages relative to previous or existing methods of belowground construction. In general, however, it is not the intention of this book to provide or duplicate existing detailed design, construction, or installation specifi cations and information as currently used by the various utilities for their belowground cable facilities. Such information is available within the individual utilities or their representative organizations. Although much of the information in this book is applicable to a variety of applications, some of the information tends to be more appropriate for specifi c portions of the power and communication networks, e.g., the local distribution system toward the customer end of the network. <br>The book is divided into six chapters. This chapter includes a description of the general categories of construction methods relevant to utility cables. Chapter 2 provides a description of underground conduit systems, including an overview of installation, operation, and maintenance procedures. Chapter 3 provides analogous information for direct-buried systems, including the limited use of pipes or ducts. A description of various methods for installing cables within ducts is contained in Chapter 4, which also includes an explanation of basic engineering principles governing such installations. Chapter 5 presents a detailed description of a particular example of a belowground cable network (BCN), including related planning, design, maintenance, and management rules for this hybrid system, which combines the advantages of direct-buried and underground conduit construction methods. Chapter 6 reviews the status of the described BCN, including the results of recent fi eld applications and anticipated future introduction into industrial applications. A glossary of terms and a list of references are provided at the end of the book. This manual is useful for new and experienced engineers alike in road and community construction, as well as utility owners, contractors, municipalities, other project owners, and other industry professionals. It provides both introductory and specifi c design and construction information to support the implementation of the proposed hybrid belowground cable network.