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Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2006. Use of Geophysics for Transportation Projects. Washington, DC: The National Academies Press. doi: 10.17226/13941.
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Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2006. Use of Geophysics for Transportation Projects. Washington, DC: The National Academies Press. doi: 10.17226/13941.
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Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2006. Use of Geophysics for Transportation Projects. Washington, DC: The National Academies Press. doi: 10.17226/13941.
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This synthesis presents the state of the industry regarding the use of geophysics on trans- portation projects. This use of geophysics on geotechnical projects is increasing among trans- portation agencies; however, the level of use varies significantly from agency to agency. In an attempt ascertain the current practice among U.S. state, federal, and Canadian transporta- tion agencies, the synthesis was undertaken to: • Review the state of knowledge; • Assess the amount and type of geophysical investigations being undertaken—by whom and how; • Discover what geophysical investigation methods and techniques are primarily used; • Determine what engineering applications geophysics are used for the most; • Assess annual budgets, in-house capabilities, and contracting practices; • Identify the approach used for selecting geophysical methods and by whom within the agency; • Ascertain the most common practices regarding Requests for Proposal solicitation and contract award; • Evaluate the level of comfort with this technology among the end-users; and • Establish if a need exists for educational and training opportunities. The objective of the synthesis is to address and document these items as they are currently being implemented by U.S. and Canadian transportation agencies. For the purpose of this synthesis, geophysics is defined as the application of physical principles to define geology and study earth (geo-) materials. Engineering geophysics is used to evaluate natural and ar- tificial foundation materials—soil and rock; however, this synthesis focuses on its applica- tion toward geotechnical problems. Information for this synthesis was acquired from a variety of sources including a litera- ture review, survey questionnaire, follow-up interviews, and requests for data solicited di- rectly from respondent agencies. A survey of practice was conducted electronically. The questionnaire was sent to 70 agency representatives, primarily in geotechnical engineering branches and sections within each of the 50 state departments of transportations (DOTs), the District of Columbia, most Canadian transportation agencies, and 7 federal agencies involved with transportation projects. A total of 63 questionnaires were returned, for a response rate of 90%. Respondents included each of the 50 state DOTs, the District of Columbia, a port authority, and 8 Canadian and 3 federal agencies. Four more responses were received as ad- ditional responses from other departments at three states DOTs. Thus, 67 responses were an- alyzed. Only 9 of the 67 agencies reported that they do not use geophysics; therefore, the data presented in this synthesis are based on answers from 58 respondents to the questionnaire. Approximately 50% of the respondents began implementing geophysics as part of their geotechnical investigations within the last 10 years; thus, for most agencies it is a relatively new investigation tool. Only a few agencies reported having in-house capabilities. Two agencies (of 58) indicated that funds are allocated annually for geophysics. The majority of agencies fund geophysical investigations through their design branches (departments) and USE OF GEOPHYSICS FOR TRANSPORTATION PROJECTS SUMMARY

procure the work under contracts to architect and engineering firms as part of their larger geotechnical investigations or under lump-sum/fixed-price subcontracts. The primary mode of solicitation among the respondents is “limited solicitation” or “sole-source” contracting. The typical number of geophysical investigations conducted each year ranges from one to five for more than half of the respondents. Contract values are predominantly less than $10,000 per geophysical investigation; however, there are agencies that routinely use geo- physics that will spend more than $100,000 annually conducting geophysical investigations. These agencies tend to carry large on-call Indefinite Delivery/Indefinite Quantity-type con- tracts to easily access qualified service providers for projects. Such contracts ranged from $300,000 per year to $5 million for 3 years (with two service providers). Between 50% and 60% of the agencies and individuals completing the survey provided an experience rating of “good” to “excellent” for their use of geophysics. However, several factors were identified as limitations to the implementation of geophysics, including difficult field instrumentation and software for data interpretation, poorly qualified service providers, and subjective and nonunique results. However, the majority of respondents indicated that inadequate understanding and knowledge of geophysics was the single greatest limitation. The results of this synthesis suggest that the majority of in-house geoscientists and engi- neers have insufficient knowledge regarding the advantages of geophysics. As experiences (e.g., case histories) are shared and educational opportunities provided for transportation en- gineers and agencies, these advantages will be better understood, which could lead to more routine use of this technology on their projects. Because highway engineers acknowledge this, the survey respondents requested that additional training resources be made available, including the development of a National Highway Institute course. Although FHWA recently published and distributed the manual, Application of Geophysical Methods to Highway Re- lated Problems, nearly 35% of the respondent agencies were not aware of it, more than half of the agencies did not have it or were not sure if they did, and approximately 45% have not used it. Since its publication in 2004 as a web-based document designed around problem solving and applications (not around geophysics), it is apparent that the effort to create the website and distribute the hard copy has not been fully realized. The ten most important results derived from this synthesis are: • Sixty-eight percent of respondents do not use geophysics very often (i.e., “occasion- ally”), and 45% of the agencies have used geophysics only in the past 10 years. • Approximately 60% of the agencies mentioned that there is an increase in their level of effort to implement geophysics, with approximately 25% indicating an increase of be- tween 50% and 100%. • The three most commonly used geophysical methods are (1) seismic, (2) ground pene- trating radar, and (3) vibration monitoring. • The top three geotechnical engineering applications for geophysics are (1) bedrock mapping, (2) mapping (characterizing) soil deposits, and (3) roadway subsidence. An interesting note is that non-destructive testing ranked second on the list; however, it is not a qualified result because it is not part of this synthesis. This point emphasizes a general lack of understanding concerning the two technologies. • The top three “greatest values” for using geophysics are (1) speed of data acquisition, (2) cost benefits, and (3) better characterization of the subsurface. • The three greatest deterrents to using geophysics are (1) lack of understanding, (2) nonuniqueness of results, and (3) lack of confidence. • Three items that can overcome the deterrents are (1) training, (2) experience (and shar- ing thereof), and (3) implementation of standards. • Very few agencies allocate funds in their annual budgets specifically for geophysical investigations, and the majority of projects cost less than $10,000. 2

• Limited or sole-source solicitations are the primary means of contracting geophysical providers; however, seven agencies are using large, on-call, multiyear contracts. • A successful-to-unsuccessful project ratio of 7:1 was shown to exist for the set of en- tire responses, and similar ratios have been observed at other agencies. Based on information gathered for this synthesis and previous discussions with hundreds of geotechnical engineers, it appears likely that as formal training occurs and successful proj- ect experiences among transportation agencies increase, using trained in-house professionals and qualified service providers, geophysics will become more widely accepted and imple- mented as another tool for the transportation industry. This synthesis determined that design and construction engineers are beginning to appreciate the benefits of geophysics through use and exposure over just the past 5 years. The majority of survey respondents believe that using geophysics has the potential to save governmental agency funds and time, and reduce the risk associated with unknown subsurface conditions. 3

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TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 357: Use of Geophysics for Transportation Projects examines the state of the practice regarding the use of geophysics for transportation projects. The report focuses on who is using geophysics and why, which methods and applications are the most commonly used, the use of in-house expertise compared with contracting private consultants, and how geophysical service contracts are procured and implemented.

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