Use of Geophysics for Transportation Projects (2006)

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23 This chapter discusses some broad issues regarding agency experience with geophysics. Areas such as the factors that af- fect comfort with the technology and their understanding of its application, what it will take to become more useful as a technology, and what will help geotechnical engineers be- come more comfortable using geophysics are reviewed. Fi- nally, there is a brief discussion of the case histories that were supplied to this synthesis. SUCCESSES AND FAILURES Part 5 of the questionnaire (Case Histories/Project Examples) solicited information regarding successful applications of geophysics, as well as the projects where geophysics did not meet the objective(s). It is important to note that projects were not defined as “successful” or “unsuccessful” by whether the investigation met the program budget or its deadlines; rather, success was solely based on if the geophysics met the objec- tives of the investigation. Figures 23 and 24 represent impor- tant results regarding agency experience. Figure 23 breaks down the total number of successful projects (714) completed over the last 5 years. This graphical presentation was neces- sary to cover the wide range of response values; that is, from six agencies with no successful projects to California’s more than 200 projects completed successfully over the past 5 years. Most of the agencies (49%) fall between 1 and 10 suc- cessful projects over this period. Nine agencies indicated im- plementing more than 20 successful geophysical projects over the 5-year period, with 2 of those agencies reporting more than 100 successful projects. Geophysics has its limitations and a discussion was pre- sented earlier (see chapter three) regarding appropriate use of the methods and techniques. Therefore, it is understandable that unsuccessful geophysical projects do occur. Figure 24 presents agency experience with geophysical investigations that did not meet the objectives (107 projects). Considering that there were about the same number of “no responses” as in Figure 23 for the past 5 years, the ratio of successful pro- jects to unsuccessful projects is approximately 7:1. This indicates that geophysics is being used successfully signifi- cantly more often than not. The agency with the greatest impact on these results—the California DOT (Caltrans)— indicated approximately 40 successful and 5 unsuccessful projects per year (a ratio of 8:1), which correlates closely with the 7:1 ratio derived from all 58 agencies responding to these questions. Therefore, based on the results of this synthesis, it appears that approximately 85% of geophysical investiga- tions are able to meet project objectives. Table C7 lists addi- tional comments regarding successful projects, unsuccessful projects, and the lessons learned by the application of geo- physics (as generated from responses to Question 60). Two replies from this table are useful to demonstrate the value of documenting successes and failures: “Our failures have pri- marily occurred when a geophysicist was not consulted on the survey design or methodology, resulting in selection of an inappropriate method or the creation of a poorly defined scope of work” (Caltrans) and “Geotechnical engineers ex- pect too much from geophysics (GPR, seismic refraction, re- sistivity) on every project they consider its use on (i.e., if it can’t give them the exact information they want, it is no good” (New Hampshire DOT). Based on the information acquired for this synthesis, as well as discussions with a number of seasoned professional geophysicists, these data are representative of the overall number of successful versus unsuccessful projects. However, within the engineering community the perception of imple- menting geophysics would imply a higher rate of unsuccess- ful projects. In general, there is a wide range in the level of comfort for use of geophysics on geotechnical projects based on the responses from this questionnaire; that is, from agency to agency the level of comfort is quite different. When asked “What could be done that would increase your level of com- fort to utilize more geophysics on projects?” (Question 55), the result was not surprising based on the data presented thus far, and that it had one of the lowest “no response” rates in the entire questionnaire (see Figure 25). Figure 25 identifies six issues that could have an impact on geotechnical engineers promoting the use of geophysics on their projects. The two most-cited issues, training/knowl- edge and experience, are what will elevate the technology to a new level of use. That is, 81% (47 of the 58 respondents) reported these two issues as being of primary importance, and only 3% (i.e., 2) of the agencies did not. Recall that only three agencies indicated that they have formal training pro- grams (chapter three). It is apparent that with time (i.e., ex- perience) and additional training (i.e., conferences and short courses) other agencies will become more comfortable with the technology. Figure 25 also reveals that as the ASTM Guides and Standards (Table 2) are implemented and further developed (see “Standards”), the level of comfort among CHAPTER SIX AGENCY PROJECT EXPERIENCE

24 engineers will increase. Then the potential exists that more successful projects will follow owing to the correct imple- mentation of geophysical techniques. It is interesting to note that between 50% and 60% of the agencies responded that equipment, software, and a database of “qualified service providers” would also help, although between 10% and 20% do not believe that this will be of assistance. Nevertheless, with additional training and experience these latter three is- sues will become less of a factor toward successful imple- mentation of geophysics among transportation agencies. CASE HISTORIES The most acceptable approach to acquiring experience is to share successful and unsuccessful project examples. The sur- vey asked for respondents to indicate if they would share case histories of either good or bad use of geophysics with others; 41% (or 22 agencies) replied “Yes” (Question 61). This represents a significant amount of knowledge to be shared with other like agencies. On request, 13 agencies sup- plied project examples for this synthesis, and 3 agencies sup- plied website links to more than one case history. It is clearly beyond the scope of this synthesis to present all the exam- ples; however, they are listed in Table 4 (including the weblinks), so that interested parties may contact an agency to obtain the example(s) and learn from these other applica- tions of geophysics to engineering problems. Based on the submitted documents, it was decided that four selected case histories would be included. Two successful (Saskatchewan and the Wisconsin DOT) and two unsuccessful (Kansas DOT and Caltrans) case histories are presented in Appendix D us- ing a simple and patterned format to address objective, re- sults, lessons learned, and conclusions. It is anticipated that the remaining case histories will be provided to FHWA for inclusion in their geophysics workshop for a more represen- tative presentation regarding the use of geophysics as applied on engineering projects. Recall that an extensive literature search produced a Topical Bibliography for this synthesis that lists many more case histories for specific geophysical methods and techniques (e.g., through conference papers). PROJECT COSTS A portion of this synthesis topic intended to determine the cost of conducting geophysical investigations. Although a few charts were presented in chapter five relating to the range of costs, the actual expense to perform an investigation is not readily available. Both Owen (22) and Rutledge et al. (23) at- tempted to provide analysis of the commercial costs without the bias of being a commercial service provider. A concerted effort was recently made by Rutledge et al. (at Virginia Tech) to directly contact more than 30 well-established geophysi- cal consulting companies within the United States with a survey/questionnaire regarding costs of performance; how- ever, only 4 responses were received, a response rate of less than 15%. Based on discussions with Rutledge, it was deter- mined that the conclusions were less than representative and therefore he “could not include absolute costing of geo- physics in the primer, because of poor response.” Two rea- sons govern the inability to discuss costing: (1) contractors do not want to provide their labor rates nor their mark-up (i.e., multiplier) and (2) transportation agencies cannot com- pare the way they would “cost” a geophysical investigation in a fashion similar to private consultants (D. Reid, personal 6 19 9 6 7 2 9 0 10 20 30 40 50 60 N um be r o f S uc ce ss fu l P ro jec ts 0 Projects 1 to 5 Projects 6 to 10 Projects 11 to 20 Projects 21 to 100 Projects >100 Projects No Response N=58 10 32 2 0 1 1 12 0 10 20 30 40 50 60 N um be r o f U ns u cc es sf ul P ro jec ts 0 Projects 1 to 5 Projects 6 to 10 Projects 11 to 20 Projects 21 to 100 Projects > 100 Projects No Response N=58 47 2 47 2 38 9 34 8 32 7 29 12 4 0 10 20 30 40 50 60 R es po nd en ts Yes No No Response N=271 Training Knowledge Experience Standards Easy Software Easy Equipment Database of Qualified Providers FIGURE 23 Number of successful geophysical projects within the past 5 years. FIGURE 24 Number of unsuccessful geophysics projects within the past 5 years. FIGURE 25 Increasing the level of comfort using geophysics.

25 Agency Case History Provided by Agency Method (Technique) Application Status Caltrans Faulting Structures for California Interstate Project Case History 1—Appendix D Seismic (Reflection) Detection of faulting U Central Federal Lands Highway Division Lava Tubes Seismic (Reflection) Resistivity (Ohm-Mapper) GPR Magnetics EM Locate voids (lava tubes) beneath the ground surface and roadway S Colorado DOT Idaho Springs Mineshaft, I-70 GPR Sinkhole/ mineshaft S Resistivity Bedrock depth UKansas DOT K-18 over the Kansas River Case History 3—Appendix D Seismic (Refraction) Bedrock depth U Massachusetts DOT Route 44 Carver, Massachusetts Resistivity (Ohm-Mapper) Detection of peat deposit Maryland DOT www.highwaygeologysymposium.org (multiple case histories available) GPR Bedrock depth and fractures SReport FHWA-NH-RD-12323U Enhancing Geotechnical Information with Ground Penetrating Radar GPR Composition, sub-bottom profiling, and voids U Resistivity Abutment imaging SRochester Bridge GPR Bedrock profile S Resistivity Bedrock profile SNH Route 25 Warren–Benton 13209 GPR Subsurface characterization S Resistivity Pipe SNH Route 102 Improvements Hudson 13743 GPR Pipe S New Hampshire DOT US Routes 4 and 202 and NH Route 9, Chichester 13922 Resistivity Assess extent of organic soil U Geotechnical Research Project Reports and Implementation Plans www.dot.state.oh.us/research/Geotechnical.htm (multiple case histories available) Ohio DOT Construction Diary of the SR32 Mine Remediation Project Constructed 1998–1999 www.dot.state.oh.us/mines/FebMar99.htm (multiple case histories available) Port Authority of New York Microtunneling at JFK International Airport Seismic (Crosshole) Microtunnel steel casings under an S & New Jersey SASW active runway S Saskatchewan Stony Rapids Airfield Case History 2—Appendix D GPR Runway subsidence S EM Delineate landfill SWisconsin DOT US Highway 53 Birch Street Interchange Site Case History 4—Appendix D GPR Delineate landfill S Notes: U = unsuccessful project case history; S = successful project case history; GPR = ground penetrating radar; EM = electromagnetic; FDEM = frequency-domain electromagnetic; SASW = Spectral Analysis of Surface Waves. Seismic (Refraction) Bedrock depth SRefraction Seismic Surveys near Falcon Lake, Manitoba FDEM Soil characterization S Manitoba I35W Bridge 9613 Vibration monitoring Establish safe vibration levels for pile driving SMinnesota DOT TABLE 4 CASE HISTORIES SUPPLIED FOR THIS SYNTHESIS

26 communication, Wisconsin DOT). Owen (22) showed hourly rates for contractors that ranged from 1.9 to 2.5 times that of the in-house rates (for GPR investigations); however, transportation agencies are not in the business of conducting geophysical investigations for profit. Information gathered for this synthesis and results derived by Tandon and Nazarian (4) concluded that the rationale for the lack of response and the inability to present “costs per method” or “costs per project” is reasonably straightforward. Simply put, sharing the confidential information a company uses to bid projects does not serve that company’s best inter- ests. Moreover, the cost to perform a geophysical investiga- tion using an academic or research institution versus a private company is not directly comparable owing to the need of a private company to include profit (i.e., make money). With that said, it is not that difficult to use assumed ranges of personnel rates and predict the number of crew members necessary for a particular technique (e.g., GPR generally needs only one person, whereas refraction can use a two- to four- person crew depending on site conditions and schedule). Sim- ilarly, equipment daily rates can be obtained on-line from a number of manufacturers and vendors that rent geophysical in- strumentation for profit. The combination of personnel rates and equipment rates can quickly yield a “crew day rate.” How- ever, it must be made clear that the crew day rate is less than half of the equation in attempting to price a geophysical investigation for any of the techniques discussed in this syn- thesis. The most significant factor controlling project cost is the “production rate.” For example, it is the line miles per day of GPR, acres per day of EM, or number of seismic spreads per day that can be completed with quality standards that dic- tates the project cost. Because the site conditions (e.g., terrain and vegetation) and the objectives (e.g., depth of investigation, size of target, and aerial coverage) on nearly every project are different, so are the proposed costs to complete the survey, even with the same geophysical technique, explaining why Owen (22), Tandon and Nazarian (4), and most recently Rut- ledge et al. (23) and this NCHRP synthesis were unsuccessful in quantifying the actual cost to perform a geophysical inves- tigation, specifically among commercial service providers.