Decision Analysis of Preferred Methods for Locating Underground Conduits

Abstract

The New Jersey DOT (NJDOT) operates and maintains a network of thousands of kilometers of conduits, many carrying fiber-optic cables that are vital to the state’s communication system. These primarily nonmetallic conduits frequently must be located and marked to avoid damage from construction. By design they can be located using a system of trace wires (TW) and radio-frequency detection. However, for various reasons the TW are missing and thus not functioning over a significant portion of the network. The purpose of the research reported in this paper was to analyze and improve the inventory information base, and find and compare effective methods for locating these conduits. Any candidate solution had to meet requirements for accuracy and depth sensitivity, be practical to implement, cost-effective, work with both metallic and plastic conduits, and be reliable. Innovative methods for locating underground conduits were investigated and evaluated with respect to various conditions. Validated approaches include enhancements to current TW methods, a new acoustic transmission (AT) method, and the ground-penetrating radar (GPR) method. The benefits of optimized location include the following: (1) reduced cost and time from more expedient systems for locating conduits, (2) less accidental damage to conduits, (3) avoidance of connectivity problems and loss of crucial communications, and (4) preservation of the fiber-optic network. A decision process identifying the optimal solution with respect to various conditions was developed and is presented in this paper. To enable the best application of the decision approach, the underlying conduit and surrounding-environment data was improved using cross-referenced geographic soil map data to enable proper selection of location technologies.