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3Problem Statement and Research Objective The ASCE 38-02 is the accepted compliance standard for many states and the SUE profession. The standard presents a four-level classification system for the quality of data for exist- ing subsurface utilities. The highest level of quality, known as Quality Level A (QL-A), requires physical exposure of any given buried utility to know and record its exact position in 3-D space. QL-A data on subsurface utilities are not influ- enced by the surrounding medium. However, the intrusive measures taken to uncover the exact positions of portions of utilities are expensive. They often do not offer a comprehen- sive understanding of the subsurface, and they can result in unsuccessful locating attempts as well as have unnecessary adverse impact on the community. Using current appropriate surface geophysical techniques to designate existing subsurface utilities or to trace a parti- cular utility system offers a nondestructive means to identify utility locations in horizontal space. The horizontal positions of geophysical anomaly sources related to underground utili- ties can be depicted on the ground surface and/or surveyed to produce a computer-aided design and drafting (CADD) or geographic information system (GIS) databases. This is con- sidered the second level of quality of data for existing sub- surface utilities and is referred to as Quality Level B (QL-B) information. Typical SUE companies, utility companies, and construction firms use pipe and cable locating geophysical sensor(s) to conduct QL-B subsurface utility investigations. In most cases, this type of geophysical investigation does not allow the detection sensor(s) data to be digitally recorded, positioned, and preserved. Data collected in this manner requires trained data collection operators who are fully experienced in understanding the analog (audio or dial) signals these detection systems produce and how to inter- pret them correctly. Thus, the data acquired are not often repeatable from one operator to the next. Also for QL-B utility investigations, the size of utility, the depth to utility from ground surface, the shape and orientation of the util- ity, the target utility composition, and the material (geo- logic or anthropogenic) surrounding the buried utility all contribute to whether utilities can be detected with geo- physical sensors. The use of a variety of complementary geophysical meth- ods and sensor configurations offers SUE professionals the best chance to comprehensively investigate and characterize the underground infrastructure. Because site conditions and the subsurface medium are never constant from location to the next, no single geophysical application can be successfully used in all locations. According to the Natural Resources Conservation Service of the U.S. Department of Agricul- ture, because of attenuation of ground-penetrating radar (GPR) signals in clay or otherwise conductive soils, only a portion of the United States is suitable for effective GPR work. Time-domain electromagnetic induction (TDEMI) can work in highly conductive soils but cannot detect non- metallic utilities without a tracer wire. Oftentimes, a com- bination of geophysical technologies is best to obtain a more complete and accurate assessment of underground utilities; as shown in Figure 1.1, GPR and electromagnetic induction (EMI) detection sensors locate specific utilities exclusively. These limitations indicate that careful consid- erations need to be taken in regard to soil type, target(s) of interest, and overall site conditions when determining which technologies of a multisensor system are proper for deployment. The purpose of the SHRP 2 R01B research was to produce multisensor geophysical systems capable of providing Qual- ity Level B data or better under any site condition and at any site location. The strategy was to develop single-pass digital geophysical mapping systems that knit data together with precision positioning and specialized software, and to develop new sensors to complement existing ones for those geo- graphic areas and conditions continuing to offer detection C h a P t e R 1 Background
45. Functional capabilities for providing on-site utility survey maps suitable for direct use by utility system designers and/or construction or maintenance contractors; and 6. Compatibility with other colocated utility detection tech- nologies to implement multisensor surveys. From the multisensor mobility viewpoint, the various sen- sor methods should have compatible ground-scanning rates and near-real-time output data displays for use by a trained system operator during the survey data acquisition process. The separate geophysical detection methodologies were to be incorporated on a compatible ruggedized platform. Work- ing prototypes for the TDEMI and the GPR system were tested and refined through this research. The basic concepts and validation behind developing a similar system using seis- mic reflection technologies was also explored. All multi- sensor geophysical systems were ultimately to be mounted on and operated from a common transport carriage either self-propelled or towed by a prime mover/data acquisition vehicle. Research team Much of the work on the project was performed by UITâs subcontractor technical team and consultants. The technical development team for this project consisted of a group of pri- vate and university researchers. Each member brought skills specific to a sensor, software, or subsystem included in the development plan. Each group and consultant was involved in the creation of the proposal ideas and the compilation of the final documents. Table 1.1 outlines the SHRP 2 R01B team members and their role in the project. challenges. The systems developed through this research were designed to produce a repeatable digital record of precisely positioned sensor detection signals which should provide information on utility locations and characteristics in 3-D space. These data can then be put into engineering context using the ASCE 38 standard while minimizing the use of test holes. These systems may also provide information to project owners, engineers, and constructors on other geotechnical conditions useful to utility design, utility condition, utility relocation, and coordination. Scope of Study The SHRP 2 R01B research focused primarily on the inte- gration of multiple yet distinct geophysical detection and positioning technologies coupled with the development of algorithmic software applications designed to facilitate geo- physical data acquisition, processing, and interpretation pro- cesses. The overall multisensor system is meant to satisfy specialized requirements which include 1. Detection, identification, and mapping of underground utility pipes and conduits in transportation rights of way where new construction or maintenance is required; 2. Resolution of pipes and conduits as small as 2 in. in diam- eter at depths of 12 ft below surface, or deeper; 3. Operation on either paved streets or roadways or on soils or backfilled utility trenches; 4. Compact hardware configuration adaptable to efficient mobile operation on streets, roadways, and adjacent terrains; Figure 1.1. The case for multiple geophysical sensors: comparing TDEMI and GPR data collected at same area.
5 Table 1.1. SHRP 2 R01B Research Team Team Member Project Role Research Area Underground Imaging Technologies, LLC (UIT) Lead Overall project management, system integration, software development, field testing Owen Engineering Services (OES) Subcontractor Seismic system development, vibrator source Psi-G, LLC Subcontractor Seismic system development and deployment Bay Geophysical Subcontractor Seismic system development and deployment Louisiana Tech University (LTU) Subcontractor Computer modeling SAIC Subcontractor Electromagnetic systems Sagentia, Ltd. Subcontractor Software and algorithm development J. H. Anspach Consulting Consultant Outreach, SUE applications, standard EM locators, liaison with user community, coordination of in-service testing Geomedia Research & Development Consultant Seismic system development, receivers Note: The organizations identified as subcontractors represent those that produced a tangible piece of the research prototypes. Consultants offered advice, helped with field testing, and consulted with SUE companies during the final validation testing phase of work.
