Current Practices and Guidelines for the Reuse of Bridge Foundations (2017)

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29 chapter three Survey reSultS A survey was distributed to 62 transportation agencies, including transportation agencies for all 50 states, Puerto Rico, and the District of Columbia, as well as ten Canadian provinces and ter- ritories. The complete survey questionnaire is provided in Appendix A and complete survey results are presented in Appendix B, both web-only documents. Forty-five of the 50 state DOTs responded to the survey, a response rate of 90% for the state transportation agencies. U.S. respond- ing agencies are shown in Figure 17. In addition, eight Canadian provinces responded to the survey. This chapter summarizes results of the survey, including general information on reuse experi- ence, the frequency of reuse for various applications, foundation investigation methods related to reuse, service life of foundations, design issues, construction techniques, and performance monitoring. Total survey responses presented in this chapter include responses from U.S. and Canadian agencies. The first survey question asked if the respondent’s agency had experience with foundation reuse. Respondents who reported that their agency does not have experience reusing foundations were asked three follow-up questions. Respondents who reported that their agency does have experience with foundation reuse were asked 22 follow-up questions. The survey was distributed to agency geotechni- cal engineers; however accompanying instructions encouraged the geotechnical engineers to share the survey with bridge or structures colleagues. Geotechnical engineers were the primary contacts since many aspects of foundation reuse, especially investigation of existing foundations, are the responsi- bility of agency geotechnical engineers. However, for many agencies, more “routine” instances of foundation reuse, especially those that maintain existing service loads, are likely completed without the input of agency geotechnical engineers. It is therefore likely that the survey results do not include all instances of foundation reuse. General InformatIon reGardInG foundatIon reuSe Responses to the first set of survey questions establish which agencies have experience with founda- tion reuse, the motivations for and against reuse, policies regarding reuse, and general information about the types of foundations that have been reused and the structures they support. Results for each topic are summarized here. agencies with foundation reuse experience For survey purposes, foundation reuse was defined as any agency action that changes the design load of the foundation. Examples of foundation reuse listed in the survey included bridge replace- ment, widening, repurposing, and retrofitting for seismic or other purposes. Bridge deck replace- ment was specifically excluded from the survey definition of foundation reuse. Fifty-one of the 53 agencies (96%) responding to the survey reported having experience with foundation reuse as defined in the survey, including all U.S. agencies except Iowa DOT. U.S. agencies with founda- tion reuse experience are shown in Figure 18. In addition, transportation agencies in Alberta, New Brunswick, Ontario, Prince Edward Island, Quebec, Saskatchewan, and Yukon indicated experi- ence, whereas the Northwest Territories DOT indicated no experience. The two respondents who reported that their agency had no experience with foundation reuse noted that they had considered foundation reuse.

30 FIGURE 17 U.S. survey agencies. Alberta, New Brunswick, Northwest Territories, Ontario, Prince Edward Island, Quebec, Saskatchewan, and Yukon also responded. FIGURE 18 Agencies with foundation reuse experience. In addition to the U.S. agencies shown in the map, Canadian agencies in Alberta, New Brunswick, Ontario, Prince Edward Island, Quebec, Saskatchewan, and Yukon indicated experience with foundation reuse, whereas the Northwest Territories DOT reported no experience.

31 motivations for and reasons against foundation reuse The 51 respondents who indicated their agencies have experience with foundation reuse were asked to select all circumstances that had motivated their agencies to reuse foundations from the responses listed in Figure 19. Economic issues were cited most frequently, by 40 of 51 respondents (78%). Accelerated construction was second most commonly cited, by 30 of 51 respondents (59%). Constructability (23 of 51, or 45%) and project schedule (20 of 51, or 39%) were also common responses. Utility conflicts were the only motivation selected by fewer than 20% of respondents. Three respondents selected “other” and reported that their agencies had been motivated to reuse foundations because the existing foundations were in good condition. It is reasonable to expect that other respondents would also have mentioned good condition as a motivation for reuse if it had been listed among the response selections. The two respondents who reported no foundation reuse experience were asked to select all the reasons their agency had not reused foundations from among the responses listed in Table 2. One respondent listed multiple reasons: uncertainty regarding existing foundations, concerns FIGURE 19 Agency motivations for foundation reuse (51 responses). Response Number Percent Uncertainty regarding existing foundations (type of foundation, plan location, depth) 1 50 Concerns regarding structural integrity of existing foundations 1 50 Concerns regarding the load capacity of existing foundations 1 50 Concerns regarding the effect of scour on existing foundations 1 50 Concerns regarding the remaining service life of existing foundations 1 50 Cheaper to build a new foundation than to retrofit an existing foundation 1 50 Concerns regarding seismic effects on existing foundations 0 0 Reuse of existing foundations is not considered in existing design codes 0 0 Unaware reusing bridge foundations was a viable option 0 0 Other, please specify: Replacement bridges have been longer and set at higher road elevations. 1 50 Two responses. TABlE 2 REASONS AGENCIES HAvE DECIDED AGAINST FOUNDATION REUSE

32 regarding structural integrity, load capacity, scour effects, service life, and it is less expensive to build new foundations than to retrofit an existing foundation. The other respondent who indicated no foundation reuse experience selected “other” and reported geometric constraints. Policies related to foundation reuse As shown in Figure 20, of the 51 respondents who indicated their agency has experience with foun- dation reuse, eight (16%) noted that their agency has policies, guidelines, or procedures related to foundation reuse. Five of the eight agencies shared their policy documents. Documents for three of the five agencies, Illinois DOT (IDOT), Maine DOT (MaineDOT), and MassDOT, include reuse policies that are generally more thorough than the other two documents, which acknowledge reuse as an option without establishing specific policies or procedures. IDOT, MaineDOT, and MassDOT are case example agencies, and their foundation reuse policies are discussed further in chapter four. Neither of the agencies without foundation reuse experience has policies related to foundation reuse, including policies that prohibit reuse. types of reused foundations and Structures Supported by reused foundations Respondents who indicated their agencies have experience with foundation reuse were asked what types of foundations their agency has reused. The responses are shown in Table 3. Most frequently reused are driven piles, with 42 of 50 respondents (84%) reporting such experience. Thirty-two (64%) have reused shallow foundations and 16 (32%) have reused drilled shafts. The rate of reuse for drilled shafts is likely lower than for piles or shallow foundations because many agency’s adoption of drilled shafts as a bridge foundation option is relatively recent. As a result, many bridges supported by drilled shafts likely have not been subject to foundation reuse. Among the other types of foundations listed by respondents were pile-supported footings and massive underwater caissons. Respondents who indicated that their agencies have experience with foundation reuse were also asked about the structures supported by reused foundations. The types of structures for which founda- tions have been reused are shown in Table 4, and traffic levels on the supported structures are shown in Table 5. All but one of the 49 respondents (98%) reported that foundations have been reused for FIGURE 20 Agencies with policies related to foundation reuse (51 respondents). Response Number Percent Driven piles 42 84 Shallow foundations 32 64 Drilled shafts 16 32 Other 8 16 Fifty responses. TABlE 3 TYPES OF FOUNDATIONS REUSED

33 bridge piers. Foundations for bridge abutments are also commonly reused, with 43 respondents (88%) indicating such experience. Fewer agencies have reused foundations for retaining walls (10, or 20%) or for arch bridges (four, or 8%). Traffic levels vary on the structures for which foundations have been reused, but for each traffic category listed, at least 30% of respondents mentioned reuse experience. aPPlIcatIonS and frequency of foundatIon reuSe Respondents who indicated their agency has experience with foundation reuse were asked about the applications for which foundations had been reused and how frequently each application for reuse had occurred in the previous ten years. As noted in the introduction to this chapter, the survey results presented in this section may underreport instances of foundation reuse since geotechnical engineers, not structural engineers, were the primary respondents to the survey and may not be familiar with all agency instances of reuse. Results related to the applications of foundation reuse are summarized in Table 6. Bridge widening and bridge replacement were by far the most common applications for reuse, with 41 respondents (82%) and 40 respondents (80%), respectively. Seismic retrofits, increas- ing clearance, and bridge repurposing were less common applications, but each was selected by at least 24% of respondents. The frequency with which each application of foundation reuse has been applied in the last ten years (2006–2016) is summarized in Figure 21. Most of the frequency values used to produce the figure are based on agency estimates, although a small number of respondents had exact numbers of applications. The sample size for each set of bars in Figure 21 is slightly less than the corresponding number of responses for each application from Table 6 because some respondents indicated that they did not have frequency information. TABlE 4 TYPES OF STRUCTURES FOR WHICH FOUNDATIONS HAvE BEEN REUSED Response Number Percent Bridge piers 49 98 Bridge abutments 44 88 Retaining walls 10 20 Arch bridge 5 10 Fifty responses. TABlE 5 ANNUAl AvERAGE DAIlY TRAFFIC OF STRUCTURES FOR WHICH FOUNDATIONS HAvE BEEN REUSED Response Number Percent AADT ≤ 1,000 24 48 1,000 < AADT ≤ 10,000 29 58 10,000 < AADT ≤ 50,000 30 60 AADT > 50,000 16 32 I don't know 4 8 Fifty responses. AADT = average annual daily traffic. TABlE 6 APPlICATIONS FOR FOUNDATION REUSE Response Number Percent Bridge widening or superstructure widening 41 82 Bridge replacement or superstructure replacement 40 80 Seismic retrofit of bridge foundations 15 30 Increase clearance (e.g., over a railway) 15 30 Bridge repurposing 12 24 Other, please specify: Scour retrofit 1 2 Cantilever retaining wall 1 2 Fifty responses.

34 The frequency of bridge widening and bridge replacement, the most common applications for bridge foundation reuse, varies among agencies with such experience. For both applications, approx- imately half of respondents reported that their agency reuses foundations for each respective purpose once per year or less. However, seven agencies reported at least five incidences of foundation reuse for bridge widening each year, and six agencies reported the same for bridge replacement. For other foundation reuse applications (i.e., seismic retrofits, increasing clearance, and bridge repurposing) incidence of foundation reuse is relatively infrequent, with at least 60% of respondents noting that their agency reuses foundations for each respective purpose once per year or less. Respondents were also asked if their agency had reused foundations for an ABC project involving PBES. ABC is a FHWA initiative intended to reduce the mobility impacts of construction projects using technology innovations such as PBES. Half of the respondents (25 of 50) reported no experience with foundation reuse for ABC/PBES projects, 14 (28%) indicated some experience, and 11 (22%) did not know. The frequency of foundation reuse for ABC/PBES projects for the 14 agencies with experience is shown in Figure 22. Eight agencies (57%) have completed one or fewer ABC/PBES reuse projects per year, three (21%) between one and two per year, and three (21%) between two and five projects per year. methodS of InveStIGatInG foundatIonS for reuSe Respondents were asked which methods their agencies have used to characterize basic details and perform condition assessment of existing foundations being considered for reuse. Similar to survey results regarding frequency of foundation reuse, it is possible results regarding foundation investi- gation methods underreport agency experiences because survey respondents likely are not familiar with every agency reuse investigation. Background information regarding investigation and condi- tion assessment methods is provided in chapter two. Table 7 summarizes responses related to char- acterization of underground portions of the foundation and Table 8 summarizes responses related to characterization of exposed portions of the foundation. For both above and below ground features, conventional records are the most common source of information, with 48 of 49 respondents (98%) using existing records for characterization of underground features and 44 of 49 respondents (90%) using inspection reports for characterization of exposed features. FIGURE 21 Average number of foundation reuse instances per year for each application.

35 FIGURE 22 Average number of foundation reuse instances per year, n, for ABC/PBES projects. Numbers listed on chart are number of agencies reporting the corresponding frequency level. Response Number Percent Research and discovery of existing records 48 98 Excavation to expose foundation (field observation) 25 51 Core drilling of foundation 21 43 Sonic echo (SE)/impulse response (IR) 7 14 Bending wave 1 2 Ultraseismic 0 0 Seismic [reflection, refraction, surface waves (SASW/MASW)], tomography 8 16 Electrical resistivity (ER)/induced polarization (IP) 1 2 Ground penetrating radar (GPR) 4 8 Parallel seismic 6 12 Magnetic logging 0 0 Cross-borehole tomography 3 6 Geophysical methods, but I don't know which ones specifically 5 10 Other, please specify: Restrike with pile driving analyzer (PDA) 5 10 Lack of settlement in response to traffic loads (i.e., observed performance) 1 2 None of the above 0 0 I don’t know 2 4 Forty-nine responses. TABlE 7 METHODS USED TO CHARACTERIzE BASIC DETAIlS AND/OR PERFORM CONDITION ASSESSMENT OF ExISTING FOUNDATIONS BEING CONSIDERED FOR REUSE Response Number Percent Inspection reports 44 90 Core drilling of foundation 31 63 Tests of concrete chloride and/or sulfate concentrations (from exposed foundation) 20 41 Sacrificial steel and inspection 10 20 Half-cell potential testing 4 8 Ground penetrating radar 4 8 Impact echo (IE) 6 12 Other 0 0 None of the above 1 2 I don’t know. 3 6 Forty-nine responses. TABlE 8 METHODS USED TO PERFORM CONDITION ASSESSMENT OF THE ExPOSED PORTION OF ExISTING SUBSTRUCTURES AND/OR FOUNDATIONS BEING CONSIDERED FOR REUSE

36 Several other methods were frequently used. Twenty-five respondents (51%) have excavated to expose portions of a foundation for observation. Twenty-one respondents (43%) have performed core drilling of the underground portions of the foundation, whereas 31 (63%) have performed core drilling on the exposed portion of the foundation or substructure. For the exposed portion of foundations and substructures, 20 respondents (41%) reported that tests of concrete chloride or sulfate concentrations had been performed, and 10 (20%) that sacrificial steel inspection had been performed. Geophysical methods were less common, but not uncommon. Five of the geophysical methods listed in Table 7 were used by at least three and as many as eight agencies (6% to 16%), and an addi- tional five respondents (10%) reported having used unspecified geophysical methods. (In interviews with case example personnel, several reported that geophysical studies are frequently undertaken by consultants rather than agency personnel.) Finally, five respondents (10%) selected “other” with regard to underground foundation investigation and indicated that their agencies had used restrikes with a pile driving analyzer as a means of condition assessment. More than 10% of these agencies have likely used restrikes when reusing pile foundations; restrikes were not included as a response selection because restrikes are primarily intended to verify load capacity rather than pile integrity. Respondents were asked to describe the availability and quality of information contained in their agency’s historical records. Figure 23 shows respondent descriptions of historical records avail- ability, while Figure 24 shows respondent descriptions of the quality of information in historical records. For both availability and quality, approximately 30% of respondents selected the best case description: historical records are always available and they always note foundation type, plan location, and dimensions. The majority of respondents indicated the second best description for both availability and quality: historical records are usually available and such records include most foun- dation information. Eleven respondents (22%) noted that historical information is available only sometimes, but that no respondent selected “never available.” Similarly, three respondents (6%) reported that foundation information is frequently missing from or conflicting in historical records, but no respondent selected “always or almost always” missing or conflicting. FIGURE 23 Availability of historical records, including as-built plans (49 responses). FIGURE 24 Quality of information contained in historical records (49 responses).

37 foundatIon ServIce lIfe The survey included a series of questions regarding service life for new and existing foundations. Twenty of 49 respondents (41%) reported that their agency explicitly considers service life as part of the design of new foundations, whereas 21 (43%) noted their agency does not consider service life and eight (16%) did not know. The 20 respondents answering in the affirmative were asked to explain how their agency considers service life in the design of new foundations. Twelve respondents provided answers, all of which are provided in Appendix B3. Examination of the 12 explanations suggests explicit consideration of service life is not as widespread as the 40% indicated by the survey responses. Only three of the 12 responses provided clear explanations of how service life is consid- ered for new foundations and these are provided in Table 9. Two other responses noted state-specific service life targets, but not how service life is evaluated for foundations. The remaining seven were either unclear, discussed existing rather than new foundations, or suggested that a 75-year service life is achieved by following AASHTO Specifications. [As explained in chapter two, AASHTO’s LRFD Bridge Design Specifications (2014) do not specify a target service life. These specifications assume a 75-year design life; however, design life is a basis for transient load determination, not the expected service life of the bridge.] Respondents were also asked how they evaluate the remaining service life of existing founda- tions being considered for reuse. Thirty of the 45 respondents (67%) did not know how remaining service life was evaluated. Most of the short answer explanations from the remaining respondents are included in Table 10. Short answer responses from all respondents are included in Appendix B3. The responses suggest that for many agencies, determining if the existing foundation will perform adequately for the target service life is central to the foundation reuse decision process even if the agencies do not explicitly determine remaining service life. The New York DOT response provided in Table 10 is an example of such a policy: rather than predict a specific value of remaining service life for the existing foundation, the agency makes a yes-or-no decision as to whether the existing foundation can be expected to be serviceable for the target service life of the rehabilitated bridge. The information used by agencies to evaluate remaining service life presumably includes the sources identified in Tables 7 and 8. Respondents were asked to identify any other sources of infor- mation used in evaluations of remaining service life and the results are shown in Table 11. loading conditions and information related to corrosion potential are among the most commonly considered sources of information. Eight respondents (17%) reported that their agency does not consider any of the sources of information in Table 11 when evaluating remaining service life. deSIGn of reuSed foundatIonS Scour and foundation reuse Respondents were asked if foundation reuse will be considered in cases where scour countermeasures are required. The responses are summarized in Figure 25. Among the 40 respondents who could answer this question there was almost an even split, with 21 respondents indicating reuse will be considered when countermeasures are required and 19 that reuse will not be considered. Additional information regarding scour issues affecting foundation reuse is presented in chapter four. TABlE 9 ExPlANATIONS OF SERvICE lIFE CONSIDERATION FOR DESIGN OF NEW FOUNDATIONS Agency Response Alberta Design of the foundation is based on ultimate and serviceability limit states. Materials selected for foundation construction are based on exposure conditions. Piers on spread footings are not permitted in rivers because of the risk of scour. New York The material requirements of state specifications have been developed to provide the required service life for typical conditions. If atypical conditions are anticipated, additional consideration is given to the design, materials, and construction procedures. Saskatchewan Pick pile types that will have longer durability, consider protective coatings, oversize piles.

38 TABlE 10 EvAlUATION OF REMAINING SERvICE lIFE FOR ExISTING FOUNDATIONS Agency Response Alberta Pier condition is inspected (primarily visually) for signs of distress. Pier is evaluated for loads based on existing geotechnical information. Florida Remaining service life has been evaluated through a combination of visual observation, coring, and in situ testing, as well as laboratory testing. Depending on the project, all or some of the following may be implemented: 1. Visual crack, delamination, and spall survey. 2. Half-cell potential survey on accessible surfaces. 3. Expose reinforcing steel for visual observation. 4. Continuity testing of the exposed reinforcement. 5. Measure concrete cover at locations where reinforcement is exposed. 6. Collect cores and perform chloride profile analysis and carbonation testing. 7. Conduct petrographic analysis. 8. Perform unconfined compressive strength testing of cores. 9. Collect soil and groundwater samples for corrosion potential evaluation (chlorides, sulfates, pH, and resistivity testing). Georgia Engineering assessment of condition and age of structure. Illinois See Chapter 4 case example. Substructure condition rating is part of reuse evaluation process. Kentucky Evaluate testing and come up with service life. Massachusetts See Chapter 4 case example. For steel piles, confirm sufficient sacrificial thickness. For concrete footings, test for chlorides in abutment or pier wall above ground. Nevada Not specifically calculated. New York The field conditions are evaluated to determine if it is reasonable to expect the existing foundation to continue to perform adequately for the proposed increase in service life. Ohio Do not evaluate remaining service life. Decision based on condition and test results. Ontario For steel piles, estimate probable rate of corrosion; add protective coating or additional sacrificial thickness. Saskatchewan Check historical file records and design loading conditions. Vermont The Structures Design Section works collaboratively with the Geotechnical Design group. We vet various ideas for determining the remaining service life, which could include records, plans, collecting and analyzing concrete cores from the abutment, etc. Response Number Percent Traffic loads 26 53 Soil/groundwater corrosion potential 20 41 Extreme event loadings 16 33 Groundwater table location and fluctuation 14 29 Subsurface drainage conditions 9 18 Winter maintenance practices 9 18 Climate 8 16 None of the above 8 16 I don’t know 6 12 Forty-nine responses. TABlE 11 INFORMATION CONSIDERED IN REMAINING SERvICE lIFE EvAlUATION, IN ADDITION TO THE INFORMATION IDENTIFIED IN TABlES 7 AND 8 FIGURE 25 Reuse when scour countermeasures are required (48 responses).

39 load capacity of foundations for reuse Methods used to predict the nominal resistance (load capacity) of existing foundations being con- sidered for reuse are shown in Figure 26. The most common method is to identify capacity from the original project documents, with 43 of 49 respondents (88%) identifying this method. Two agencies indicated by means of “other” responses that they modify the capacity value from the original bridge project documents by applying a current agency dynamic pile driving formula to the pile driving record for the existing pile. One such agency, Illinois DOT, is a case example agency discussed further in chapter four. It is likely other agencies adopt a similar approach to modifying the original capacity value even if they did not mention such in the survey. Static analysis methods are also commonly used, with 28 respondents (57%) identifying this method. Seven of the 49 respondents (14%) have used load testing to evaluate nominal resistance. Of those seven agencies, four have used high-strain dynamic load tests, two conventional static load tests, and one has used a test vehicle. design codes for reused foundations As shown in Table 12, the most common design standard applied to reused foundations is the AASHTO specifications from the date of reuse, with 31 of 39 U.S. respondents (79%) indicating such experience. However, nearly 40% of respondents had also applied the AASHTO specifications from the date of original foundation construction, and 11 (28%) had applied state-specific provisions. Among Canadian respondents, six noted that they used the Canadian Highway Bridge Design Code; while one, New Brunswick, reported that it uses province-specific provisions. Design methodologies (i.e., working stress versus reliability-based design) applied to reused foun- dations are shown in Figure 27. Working stress design methods have been applied most frequently Response Number Percent AASHTO specifications from date of foundation reuse 31 79 AASHTO specifications from date of original foundation construction 15 38 State-specific provisions 11 28 Thirty-nine responses, U.S. agencies only. TABlE 12 DESIGN STANDARDS USED TO EvAlUATE FOUNDATIONS TO BE REUSED FIGURE 26 Methods used to predict nominal resistance of existing foundations being considered for reuse (49 responses).

40 (19 of 49 respondents, 39%), but reliability-based design methods are also common (15 of 49 respon- dents, 31%), and nearly 20% of the respondents mentioned that they use the methods nearly equally. Respondents were asked to identify how their agencies have evaluated reliability for foundations to be reused. Most responses cited AASHTO or state-specific lRFD criteria. A full listing of responses is included in Appendix B3. conStructIon technIqueS and Performance monItorInG The construction techniques used to facilitate foundation reuse are shown in Figure 28. The frequency of use varied by technique; however, seven of the techniques had been used by at least one-quarter of respondents: addition of driven piles (73%), enlarged footing (63%), addition of micropiles (52%), FIGURE 27 Design methodologies applied to reused foundations (49 responses). FIGURE 28 Techniques used to facilitate foundation reuse (48 responses).

41 addition of drilled shafts (44%), pier stem widening (44%), addition of tiebacks (29%), and replace- ment of backfill with lightweight fill (27%). The frequency of agency performance monitoring for new and reused bridge foundations is shown in Figure 29. For both new and reused foundations, approximately 25% of agencies always monitor performance, another 25% of agencies sometimes monitor performance, and 35% to 40% of agencies never monitor performance. The biggest difference in responses between new and reused founda- tions is in the number of respondents who did not know the proper selection. Respondents were also asked how performance is monitored. Of 17 responses, 13 explained that performance was monitored through regular agency bridge inspections, while four others mentioned monitoring for movement by means of surveying or instrumentation. The complete set of responses is included in Appendix B3. Summary of SIGnIfIcant fIndInGS • Ninety-eight percent of responding agencies have experience with foundation reuse, which was defined as any agency action that changes the design load of a foundation. The three survey respondents without experience had all considered reusing foundations. • Respondents cited many reasons for foundation reuse. Economic issues were cited most fre- quently, by 78% of respondents. Accelerated construction (59%), constructability (45%), and project schedule (39%) were also commonly cited. • Eight agencies have policies related to foundation reuse. Most of these policies are not stand- alone policies regarding foundation reuse; rather, they are broader agency documents that address foundation reuse to varying extent. • Pile foundations have been reused most frequently, by 84% of survey respondents. Shallow foundations have also been reused frequently (64%). • Bridge widening and bridge replacement are by far the most common applications for founda- tion reuse, with 82% of respondents having experience with the former and 80% with the latter. Approximately one-quarter of respondents have experience reusing foundations for seismic retrofits, increasing clearance, and bridge repurposing. • Seven agencies reported at least five incidents per year of foundation reuse for bridge widening and six reported the same for bridge replacement. Most of the remaining agencies with relevant experience reported one or fewer incidences per year on average. Incidence rates of about one per year were also reported for most agencies for the other applications of foundation reuse. The incidence rates reported in the survey may underreport actual rates because agency geotechnical engineers may not be familiar with every instance of foundation reuse. • Nearly all agencies rely on historical records such as as-built plans and inspection reports to char- acterize and perform condition assessment of existing foundations. About half of agencies have excavated to expose portions of the foundation for observation and about half have performed core drilling of foundations. Use of geophysical methods was less common but not uncommon, with five different methods having been used by at least three and as many as eight agencies. (a) (b) FIGURE 29 Frequency of performance monitoring for (a) new and (b) reused foundations (49 responses).

42 • Two-thirds of respondents did not know how their agencies evaluated remaining service life when considering foundation reuse. Survey responses suggest remaining service life is typically considered implicitly in reuse decisions rather than explicitly evaluated. • Among 40 question respondents, about half will consider foundation reuse when scour counter- measures are required. • The most common method of predicting nominal resistance of existing foundations is to identify values from the original project documents, with 88% of respondents indicating such experience. • AASHTO specifications from the date of foundation reuse have been used by 79% of respon- dents, whereas 38% of respondents have experience using AASHTO specifications from the date of original foundation construction. • Design methodologies applied to reused foundations were split approximately evenly between working stress design and reliability-based design, with slightly more agencies indicating working stress design. • Seven different construction techniques had been used by at least one-quarter of respondents. Most commonly used were the addition of driven piles (73%), increasing footing size (63%), and addition of micropiles (52%). • For both new and reused foundations, approximately half of agencies either always or sometimes monitor performance. Of 17 explanations of how performance is monitored, 13 reported that per- formance was monitored through regular agency bridge inspections, while four others mentioned monitoring for movement by surveying or instrumentation.