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5This chapter discusses the general nature of geophysics, its past and current use, particularly by transportation agencies. It also presents the objective, scope, and organization of the synthesis. BACKGROUND Geophysical methods have been used for nearly 70 years, although predominantly in the exploration for natural re- sources. Oil, gas, and mineral exploration demanded better technologies to locate and define highly needed natural re- sources before and during World War II (1). Since the 1950s, the use of geophysics in the natural resource exploration in- dustry has increased to the point that it is used as the first level effort on every project. Drilling and other physical means of defining the geologic setting, composition, and depth of interest are used after imaging the subsurface be- neath the property through successful application of geo- physics. The use of geophysics among U.S. state departments of transportation (DOTs) and Canadian transportation agencies varies widely depending on the knowledge of the individuals and the combined experiences of the transportation agency. Over the past decade there has been an increased effort on the part of the engineering geophysical community to provide technologies that aid the design and construction needs of transportation projects. In the most generalized sense, geophysics is the applica- tion of physical principles to define geology and study geo- materials; for example, soil or rock (2). The following para- graph from the Introduction to Geophysical Prospecting (3) presents the best formal definition of geophysics: We designate the study of the earth using physical measure- ments at the surface as geophysics. While it is not always easy to establish a meaningful border line between geology and geophysics, the difference lies primarily in the type of data with which one begins. Geology involves the study of the earth by direct observations on [soils and] rocks, either from surface exposure or boreholes, and the deduction of its structure, composition, or history by analysis of such obser- vations. Geophysics, on the other hand, involves the study of those parts of the earth hidden from direct view by measur- ing their physical properties with appropriate instruments, usually on the surface. It also includes interpretation of the measurements to obtain useful information on the structure and composition of the concealed zones. Geophysics affords the opportunity to cost-effectively sam- ple large volumes of the subsurface using such principles as seismic- or electromagnetic (EM)-wave transmission, electri- cal current flow, and magnetic and gravity potential fields. The science is technical in its application, and is quantitative in its measurement, yet it provides only the qualitative information about geomaterial properties needed by engineers. For exam- ple, it does not directly measure density, moisture content, or stiffness, but provides a relationship between a measured value (e.g., seismic velocity) and the physical parameter that governs it (e.g., density). It is the complement of using a broad view of the subsurface imaged from a geophysical investigation and data directly obtained from drilling that creates the value and benefit of this technology. Those responsible for design and construction on sites that pose significant risk to society require the most advanced technologies to better characterize the distribution of physical properties in the subsurface. The purpose of using geophysics, as defined for this synthesis, is to identify and characterize physical properties of subsurface geomaterials in a manner that benefits highway projects and transportation programs. These benefits can be associated with reduced project costs, better and broader subsurface characterization, increased speed of acquisition, and utilizing a noninvasive approach to evaluate subsurface conditions. It can be construed that because it was not until 1992 that an international professional geophysical society was formed [the Environmental and Engineering Geophysical Society (EEGS)], the use and application of geophysics for shallow investigations (30 m/100 ft) is relatively new. Over the past 10 years the increased need to reduce risk for the design and construction of engineered structures has dictated better in- strumentation and data processing software, as well as added educational opportunities, to effectively make geophysical technologies available. EEGS and its members have worked to educate end-users on the correct application of geophysics. The emergence of non-destructive testing (NDT) technol- ogy is even more recent. Although the science of NDT has un- dergone approximately 10 to 12 years of development, it has become standard practice in the transportation industry for only the last 6 to 7 years. For the purposes of this synthesis, it is important to distinguish between the terms âgeophysicsâ and âNDT.â NDT uses many (if not all) of the physical prin- ciples used in geophysics; however, it is the application of the CHAPTER ONE INTRODUCTION
6technology that separates the two. NDT is used to image and evaluate engineered structures; that is, man-made features such as bridges, walls, and drilled shafts. OBJECTIVE In early 2005 (before the completion of this synthesis), Tandon and Nazarian reported that the use of geophysics on trans- portation projects varied significantly among DOTs (4). The objective of this synthesis is to determine the state of the prac- tice and level of knowledge regarding the use of geophysics among transportation agencies. This synthesis focuses on U.S. state DOTs and U.S. federal and Canadian provincial trans- portation agencies. The main points addressed are who is and who is not using geophysics, and why; which geophysical methods and applications are most commonly used; trends re- lated to in-house expertise versus contracting private consul- tants; how geophysical service contracts are procured and implemented; experiences gained and lessons learned through case histories; and identification of future needs. SCOPE Although this synthesis discusses a broad range of topics re- lated to the actual day-to-day implementation of geophysical technologies, the main goal is to summarize the overall use of these technologies in the United States and Canada. The scope of this project was limited to how geophysics is being applied by geotechnical engineers during highway planning and construction activities. The emphasis is on the use of geophysics for geotechnical issues as they relate to natural and artificial foundations. The majority of information included in this synthesis was obtained from published literature, the electronic survey and questionnaire (see Appendix B), and interviews. A compre- hensive survey was developed and sent electronically to rep- resentatives in all 50 states and the District of Columbia, the Canadian provinces, and other federal government entities with experience in geophysical applications. Follow-up tele- phone interviews, to clarify or expand on particular aspects of some survey responses, were also conducted. The e-mail survey method proved very effective. A total of 70 questionnaires were sent and 63 agencies replied, for a 90% response rate. Figure 1 shows that a total of 67 ques- tionnaires were returned from 58 agencies: 56 from U.S. state DOTs (including the District of Columbia and the Port Au- thority of New York and New Jersey), 8 from Canadian agencies, and 3 from U.S. federal agencies. Three states re- turned multiple responses [Colorado (2), Michigan (2), and Oregon (3)]; therefore, a total of 56 state DOT agency re- sponses were received. Their answers were tallied appropri- ately into the database, but the individual state DOT was con- sidered as a single agency response. The questionnaire was sent to three other organizations: Kansas Geologic Society (a state agency), University of Missouri at Rolla (an educational institution), and Technos, Inc. (a private consulting firm), re- spectively. They were selected based on their qualifications and experiences with the transportation industry and queried to determine the validity of the survey. These three organi- zations replied promptly and agreed that they should not be included as respondents because their use of geophysics is not discretionary. Based on their responses and follow-up in- terviews, no additional questionnaires were sent to educa- tional institutions or private consultants. This specialized synthesis on the use of geophysics ne- cessitated that agencies that do not use geophysics respond appropriately to Questions 14, 15, and 21L, so that they would not be included in the analysis. Figure 1 charts the re- sponses to these questions and the distribution of U.S. state and federal and Canadian agencies that either use (responded âyesâ) or do not use (responded ânoâ) geophysics. Only 9 agencies indicated that they do not use geophysics at all; therefore, 58 total responses (including the 4 extra from 3 state DOTs) is the base number in the analysis of the use of geophysics in transportation. ORGANIZATION Chapter two provides results from the literature search. It dis- cusses the difference between educational materials and in- formational materials regarding application of geophysics to highway-related projects. The chapter will identify standards (e.g., ASTM) related to geophysical investigations. The ap- proach to selection of geophysical methods and techniques is discussed and a matrix summarizing geophysical techniques versus geotechnical applications is presented. Chapter three covers the method of data collection and analysis for the NCHRP survey. It discusses, in general, the demographics of the survey and the type of information re- quested, and then presents specific examples regarding the use of geophysics among the respondent transportation agencies. 50 6 6 2 2 1 0 10 20 30 40 50 60 R es po nd en ts DOTs Yes DOTs No Canadians Yes Canadians No Federal Agencies Yes Federal Agencies No N=67 FIGURE 1 Breakdown of agency response to use of geophysics.
7At the end of the chapter, NDT will be discussed as it relates to this synthesis and briefly how it is used by the respondents. Chapter four presents the geophysical methods, tech- niques, and applications. It presents the very broad and diverse use of geophysical methods as currently used on transportation projects. Because chapter three is directed to- ward the process of gathering the survey information, this chapter focuses directly on geophysical methods and geo- technical engineering applications. Chapter five focuses predominantly on identifying the ap- proach used by DOTs to procure geophysical service providers and discusses agency programs regarding budgets and contracting. The discussion is focused on allocation of funds, funding sources, and contracting methods and needs. Chapter six discusses both successful applications and those that were deemed to be unsuccessful. A table shows the case histories that were provided for this synthesis that includes a brief description of the method used, application, status, and if the project was successful or unsuccessful. An important component of this chapter will be an evaluation of the benefits observed from both successful and unsuccessful projects. A brief discussion regarding the current level of comfort and what will increase the level of comfort among engineers and agencies to implement geophysics will be presented. Chapter seven summarizes synthesis results. This chapter includes recommendations for future research regarding geo- physical investigations, as defined by the respondents, and concluding remarks.
