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

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

43 chapter four Case examples The survey results presented in chapter three were used to select five agencies for further case exami- nation. The agencies were primarily identified based on responses that revealed that the agency had unique policies related to foundation reuse, frequent experience with foundation reuse, or experience on noteworthy foundation reuse projects. The agencies selected were Maine, Illinois, Massachusetts, Missouri, and Colorado DOTs, and Ontario Ministry of Transportation. For each, the survey contact was interviewed and agency documentation was reviewed to identify unique experiences and help- ful lessons regarding foundation reuse. Results of each case example are presented in this chapter. maine Department of transportation MaineDOT first included foundation reuse guidelines in the 2003 version of its Bridge Design Guide (MaineDOT 2014). The guidelines include specific investigation and analysis procedures for several types of existing foundations. During its agency interview, MaineDOT explained that the founda- tion reuse guidance was developed to satisfy the agency’s due diligence and to provide a rational approach to foundation reuse. The agency also explained that the guidelines were developed based on reuse experience on prior agency projects. MaineDOT reported in its survey response that foundation reuse is primarily motivated by accel- erated construction and economic issues, and that the agency reuses foundations about once each year for ABC projects and once or twice a year for superstructure replacements. The agency has used many different methods, including geophysics, for investigating existing foundations. The following sections summarize the agency’s reuse guidance and practices related to scour and foundation reuse. Two prominent examples of foundation reuse by MaineDOT are also highlighted here. foundation reuse Guidance in maineDot’s Bridge Design Guide Foundation reuse is addressed in the Bridge Design Guide in Chapter 10, “Bridge Rehabilitation.” The chapter introduction recommends that life-cycle cost analysis be completed to confirm that rehabilitation is preferred over replacement. Section 10.7, “Substructure Reuse,” includes the most pertinent information related to foundation reuse. The introduction to this section calls for evalua- tion of existing foundations whenever the substructure is to be reused “with new loads applied,” a description similar to the definition of foundation reuse provided with the survey for this Synthesis. The introduction also recommends exploration and testing to determine the geometry and condition of unknown foundations, as well as structural analysis to evaluate the effect of any deterioration. The remainder of Section 10.7 details procedures for two types of foundations: timber piles and granite or stone substructures. The guide recommends investigation and analysis procedures, but does not include any specific requirements for reuse, noting for both types of foundations covered in the guide that the reuse evaluation “needs to be appropriate to the particular site.” For timber piles, the guide lists five types of investigations, one of which is evaluation of groundwater and subsurface conditions through borings. Two of the remaining investigations relate to condition assessment and the other two are for load capacity. For condition assessment, recommended procedures include the sonic echo/impulse response test and coring the timber to evaluate the condition of the pile and to determine if marine borers are present (see “Deterioration of Timber” in chapter two of this Synthesis). Recommended procedures for load capacity of timber piles include using boring information to

44 predict capacity by means of static analysis methods and performing a static load test to 2.5 times the proposed design load. MaineDOT’s Bridge Design Guide also includes provisions regarding reuse of granite and stone abutments. These abutments are generally historical but not historically significant. The cross-sectional shape of the granite and stone abutments is variable: some are similar to massive gravity retaining walls, others are a single block thick, and still others are less well-defined, or “rubble masonry.” Five general steps outline the “typical” procedure for preliminary evaluation of the reuse of granite and stone abutments: 1. Review any existing records, including as-built plans. 2. Perform condition assessment by means of field investigation of the abutments. It is important that the field investigation include observations of any foundation instability, drainage issues, deterioration of stones or mortar, bulging or rotating stones, cracked stones, and previous modifications to the abutments such as concrete facing. 3. Perform condition assessment by subsurface investigation techniques. Techniques are to be “appropriate to the particular site” and may include: – GPR to determine abutment geometry – Conventional borings to verify abutment and foundation geometry and to gather informa- tion regarding the wall backfill and foundation material – Test pits to confirm foundation material and foundation dimensions and depth – Seismic geophysical methods to identify abutment geometry. 4. Using the results of the investigation, determine if the existing substructure is compatible with the proposed bridge alignment, width, grade, and loads. 5. Perform a cost analysis to compare reuse with replacement. The cost of reuse should include any necessary retrofits. If reuse is recommended, additional analyses of the substructure should be completed for final design according to Chapter 5 of the guide, “Substructures.” Chapter 10 of the Bridge Design Guide also includes provisions related to bridge widening. The guide recommends widening to one side of the bridge for constructability reasons. The guide also recommends geotechnical analysis be performed to determine whether the widened portion of the bridge can be cantilevered or should be supported by a widened substructure. Finally, Chapter 10 of the Bridge Design Guide includes provisions for substructure rehabilitation. The provisions include recommendations for “underpinning” existing pile caps or shallow spread footings to improve sub- structure load capacity or to correct angular distortions resulting from “inadequate bearing capacity.” Underpinning is achieved by the addition of driven piles or micropiles to the existing pile cap or footing, which may need to be widened to support the additional foundation elements. scour and foundation reuse at maineDot During its agency interview, MaineDOT indicated that the limited number of examples of bridge failures in the agency’s history was all attributed to scour, and as a result the agency is “keenly aware” of scour issues. MaineDOT generally uses HEC-18 (Arneson et al. 2012) for evaluation of scour. In 2002, USGS and MaineDOT published a study (Hodgkins and Lombard 2002) that com- pared observed and predicted pier scour in Maine for eight bridges across the state for high-flow events that occurred during a 4-year period. The study concluded the Colorado State University equation for predicting pier scour is reasonable for use with Maine bridge piers. The equation is the basis for predictions of pier scour in the 2012 version of HEC-18. MaineDOT’s Bridge Design Guide (2014) requires scour evaluation of all bridge rehabilita- tion projects for which the project scope “exceeds deck, wearing surface, or rail rehabilitation/ replacement.” Details of the scour evaluation are included in chapter two of the guide. For existing bridges, the scour evaluation is intended to determine whether or not the bridge is scour-critical. The agency identifies bridges with observed scour and bridges with scour potential per HEC-18 evalua-

45 tion as scour-critical. For bridges identified as scour-critical, investigation of scour countermeasures is included in design of the rehabilitation project. The countermeasures may include regular inspec- tions if consultation with the agency’s Bridge Maintenance division concludes inspections are an “acceptable method to reduce the risk of failure.” If not, hydraulic analysis is performed to design scour countermeasures per HEC-23 (Lagasse et al. 2009). The scour countermeasures may include riprap aprons depending on the design flow velocity. example project: U.s. route 1 Viaduct reconstruction A 1,300-ft long, 20-span viaduct carries U.S. Route 1 over local streets in Bath, Maine, before con- necting to the Sagadahoc Bridge over the Kennebec River. The viaduct was constructed in 1957 and has had several repairs and rehabilitations in its lifetime, including installation of a new surface in 2006 that was intended to extend the life of the viaduct by 10 years. In 2016, MaineDOT will replace the viaduct from the ground up, reusing the foundations but replacing the rest of the bridge including the pier columns and caps. To reduce mobility impacts associated with closure of the 18,000 ADT viaduct, the majority of the replacement work will be completed during the off-peak tourist season between October 11, 2016, and May 25, 2017, and the contractor will be permitted to work 24 hours a day, 7 days a week during the closure. Foundations for 11 of the bridge piers and one of the abutments are on steel H-piles (HP 10×42) driven to bedrock. The other eight piers and abutment are on spread footings on bedrock. Sub- surface information for the bridge includes information from the original bridge construction as well as several investigations completed for the rehabilitation project. The original investiga- tion included rod soundings driven to refusal and test borings; the rehabilitation investigations included test borings, test pits, and nondestructive testing. Three rehabilitation investigations were directed by a MaineDOT consultant and are summarized in separate reports (Haley & Aldrich, Inc. 2013, 2014, 2016). The first investigation consisted of test borings and laboratory testing including soil corrosivity tests; results were used to assist in preliminary decisions and designs for the rehabilitation. The second investigation included test pits, nondestructive testing, and additional test borings to perform condition assessment of the existing foundations and sup- port final design of the rehabilitation. The third investigation included supplemental borings to support design of sign structures. Boring information indicated that the subsurface profile at the bridge site generally consists of sandy fill overlying marine clay, glacial till, and bedrock. The fill layer is sandy and approximately 5 feet thick. The marine clay is soft, and the thickness of the deposit varies from approximately 5 feet on the west end of the site to 38 feet on the east end of the site near the Kennebec River. The glacial till layer includes clay, sand, and gravel and is less than 5 feet thick. The first foundation report (Haley & Aldrich, Inc. 2013) compares subsurface information from the historical investigation with that from the rehabilitation investigation. Differences in the survey datum that was used for the historical investigation and for the rehabilitation investigation complicated the comparisons. The MaineDOT consultant resolved the difference by comparing “side-by-side” historical and rehabilitation borings on the east end of the site, where the marine clay deposit is thickest. The survey datum conversion based on the side-by-side borings was applied to other historical borings to plot historical subsurface information on the current elevation datum. The results revealed close agreement in values of com- pressibility, stress history, and undrained shear strength of the marine clay layer between the historical investigation and the rehabilitation investigation. Results from the first rehabilitation investigation were used to evaluate the feasibility of reusing the existing foundations considering their geotechnical capacity. The consultant predicted geotechni- cal capacity based on AASHTO LRFD specifications. For spread footings, the consultant predicted a factored bearing resistance of 20 kips per square foot considering both presumptive values for the type of bedrock as well as calculations of bearing resistance for jointed rock based on rock mass rating. The structural consultant (separate from the geotechnical consultant) provided conservative load estimates for a new superstructure with updated live loading. The resulting contact pressures, between 7 and 8 kips per square foot, are less than the factored resistance; therefore, the existing

46 footings were recommended for reuse pending further evaluation in final design, including analysis of lateral load. The feasibility of reusing the driven piles was evaluated by comparing the predicted vertical pile loads for the rehabilitated bridge with the pile design loads shown on the final plans for the original bridge construction. The predicted loads were less than the original design loads; therefore, the driven piles were also recommended for reuse pending further investigation of pile condition, length, and capacity. The second rehabilitation investigation included test borings to provide additional subsurface information, as well as test pits and nondestructive testing to evaluate pile length and perform condi- tion assessment of the driven piles at five piers and one abutment. Initially, test pits were excavated to depths of 3 to 4 feet to expose the pile caps and strike them as part of parallel seismic testing to estimate pile length. Subsequently, the test pits were excavated to depths of 8 to 9 feet to assess the condition of the top 2 feet of the pile. During the first rehabilitation investigation, the consultant concluded that piles were likely driven to bedrock based on comparison of subsurface information and estimated pile lengths shown on the final construction plans and construction diaries from original construction. During the second rehabilitation investigation, pile length was first evaluated using the parallel seismic method; upon completion of the parallel seismic testing, MaineDOT supplied as-built records of pile length. The parallel seismic method was presented in chapter two and shown schematically in Figure 6 of this Synthesis. A photograph of the application of the method for the U.S. Route 1 bridge is shown in Figure 30. The testing was performed by a firm specializing in geophysics and is documented in a supplemental report to the second investigation (Olson Engineering 2014). Results of the parallel seismic testing are summarized in Table 13, which also shows information from the as-built plans and subsurface investigations. The consultants noted that pile length varies within pile groups and that the pile lengths estimated from parallel seismic testing likely reflect the length of the pile closest to the borehole used for testing. For Pier 19, results were interpreted as two values for different piles of significantly different length. The parallel seismic pile length estimates are generally within or near the range for each group indicated by as-built plans and construction diaries. The consultants note that the pile lengths are highly variable between and within pile groups as a result of a “highly erratic” bedrock surface. The consultants concluded that the piles are likely bearing on bedrock because the pile tip elevations from the as-built plans, construction diaries, and the parallel seismic estimates are generally close to the bedrock elevations from historical and rehabilitation boring explorations. FIGURE 30 Parallel seismic testing of abutment piling for the U.S. Route 1 bridge in Bath, Maine. The 4-lb hammer was used to strike the concrete pile cap, and the response was measured from a hydrophone inside the PVC casing (arrow) (Source: Olson Engineering 2014).

47 Test pits at four of the piers were excavated to depths below the pile caps to inspect the piles for evidence of corrosion. Photographs of the test pit investigation are shown in Figure 31. The investi- gation did not reveal any visible evidence of significant corrosion, although minor “chipping of an apparent pile coating” was observed for one pile and “slight pitting” was observed on a different pile. Caliper measurements of flange thickness were all greater than or equal to the specified thickness from the date of construction. The consultants also noted that the subsurface environment—naturally deposited soil with a static groundwater level near the bottom of the pile cap—is associated with a relatively low risk of corrosion. The recommended design value of axial pile capacity in the consultant report (Haley & Aldrich Inc. 2014) is the structural resistance with a reduced section to account for potential corrosion. Struc- tural resistance controls based on the conclusion from subsurface investigation, review of as-built plans, construction diaries, and parallel seismic testing that the piles are bearing on bedrock. Although no corrosion was observed, the consultant reduced the pile cross section by 1/32 inch along all edges of the H-pile when calculating the axial capacity. The reduced cross section, corresponding to a 20% section loss, was intended to account for potential corrosion in piles that were not exposed by test pits and for potential corrosion during the intended 75-year service life extension. The AASHTO struc- tural resistance factor for axial capacity was applied. Finally, the consultant report documents preliminary substructure analysis that was performed to determine if the pile groups would need modification to increase capacity. Much of the information for the analysis was provided by the structural consultant, including two superstructure alternatives as well as varying load combinations. The live loading for the analysis was HL-93, the current AASHTO standard, although MaineDOT typically designs for a modified version of HL-93 with greater loads. Analysis was completed using FB-MultiPier, a nonlinear finite element program for interconnected bridge substructures that considers soil–structure interaction. The analysis indicated that the preliminary loads provided by the structural consultant would result in pile loads exceeding the factored axial resistance for most pier locations. In the preliminary report, the consultant recom- mended the addition of micropiles if the final design analysis also indicated pile loads exceeding the design capacity. However, final design of the bridge rehabilitation resulted in reduced loading. MaineDOT explained during its agency interview that preliminary design loads are generally conser- vative to prevent final designs being costlier than preliminary estimates. Final bridge rehabilitation plans include replacing the entire bridge from the ground up and reusing the foundations without replacement. Construction was scheduled to begin in Fall 2016. example project: Haynesville Bridge The Haynesville Bridge carries U.S. Route 2A over the Mattawamkeag River in Haynesville, Maine. U.S. Route 2A is a low-volume road in Haynesville, with average annual daily traffic (AADT) of approximately 400 vehicles per day. The Haynesville Bridge was constructed in 1953 Location Pile Length, feet Pile Tip Elevation, feet Top of BedrockElevation, feet As-built Lower Bound As-built Upper Bound Parallel Seismic As-built Lower Bound As-built Upper Bound Parallel Seismic Historical Boring Rehab Boring Pier 5 9.3 13.9 9.2 10.2 14.8 14.9 14.3 15.4 Pier 7 15.7 37.2 13.5 −17.4 4.1 6.3 −2.4 3.5 Pier 10 9.8 18.7 19.7 −4.5 4.4 −5.5 1.8 −4.3 Pier 19 31.3 46.2 20.3, 37.7 −42.7 −27.8 −17.2, −34.6 −30.2 −37.9 Abutment 2 24.7 44.8 30.0 −40.0 −19.9 −25.2 −28.2, −23.4 −30.6 Based on information from Haley & Aldrich, Inc. (2014) and Olson Engineering (2014). TABLE 13 COMPARISOn OF PILE LEnGTHS FROM AS-BUILT DRAwInGS AnD COnSTRUCTIOn DIARIES AnD PARALLEL SEISMIC METHOD FOR THE U.S. ROUTE 1 BRIDGE In BATH, MAInE

48 as a three-span steel girder bridge with two mass concrete stub abutments on treated timber piles and two solid wall piers on untreated timber piles. A 2014 MaineDOT inspection report revealed several concerns with the superstructure: fracture-critical pin connections in serious condition, struc- tural steel in overall poor condition (nBI condition rating 4), and areas of moderate to advanced section loss in the steel. The same report noted that the substructure was in satisfactory condition (nBI rating 6). In 2015, MaineDOT decided to replace the superstructure while reusing the substructures and pile foundations without modification. To evaluate reuse of the foundations, MaineDOT performed condition assessment, completed static load tests, and estimated capacity of the existing timber piles. The investigations and analyses are summarized in an agency geotechnical report (Krusinski 2015). FIGURE 31 Photographs of test pits for the U.S. Route 1 bridge in Bath, Maine: (a) view from inside the test pit through the trench box showing two exposed piles (HP 10×42) beneath pile cap, (b) close-up view of exposed pile flange, (c) close-up view of pile flange thickness (Source: Haley & Aldrich Inc. 2014). (b) (c) (a)

49 Subsurface conditions at the Haynesville site generally consist of alluvial sand with silt and gravel over glacial deposits of sand, silt, and gravel. Bedrock is encountered beneath the glacial deposits, with the top of the bedrock generally 25 to 35 feet beneath the riverbed. For the foundation reuse investigation, MaineDOT completed four borings, one at each abutment and each pier, using an agency drill rig and crew. The borings included SPT data in the sand and a 5-foot core run of bedrock. Laboratory testing primarily consisted of grain size analyses. In addition, one direct shear test was performed on a reconstituted sand specimen. Field investigation of the timber pile foundations included condition assessment by pile integrity testing, as well as static load testing. The pile testing was performed by a MaineDOT consultant (GZA GeoEnvironmental, Inc. 2014). One pile at each abutment was investigated; pier piles are submerged by the river, making field investigation impractical. The existing abutments are founded on two rows of 12 timber piles. Excavation for the investigation exposed two outer piles at each abutment, one in the front row and one in the back row. The excavations exposed approximately 4 feet of each pile; visual observation did not reveal any signs of decay. After exposing the piling, a 19-inch length was removed from the test pile at each abutment as shown in Figure 32. Interestingly, the 19-inch segment of the north abutment test pile was removed easily, suggesting that any compressive load in the pile was negligible. In contrast, the chainsaw was pinched during removal of the 19-inch segment of the south abutment test pile, requiring wedges to complete the removal and suggesting a significant compressive load in the pile. After freeing the bottom portion of the pile, the pile diameter at the top of the free length was measured: 10.9 inches for the north abutment test pile and 12.6 inches for the south. Sonic echo/impulse response pile integrity testing was conducted on the bottom portion of each test pile to assess pile length. Four hammers, each with a different weight, were used to generate the test impact. The test results indicated pile toe depths below the impact location of 32 feet at the north abutment and 26 feet at the south abutment. Considering the length of pile above the impact location, the results of the pile integrity test are gener- ally consistent with the original final plans for the bridge, which estimated pile lengths of 35 feet at each abutment. After the pile integrity tests were complete, the MaineDOT consultant performed a static load test on each test pile. Tests were done by placing a hydraulic jack in the 19-inch gap where the length of pile had previously been removed as shown in Figure 33. The reaction force for the test pile load was therefore provided by the pile cap and the other piles in the group. The test procedure was generally in accordance with ASTM D1143 Standard Test Methods for Deep Foundations FIGURE 32 MaineDOT consultant uses a chainsaw to cut a timber pile supporting the Haynesville Bridge (Courtesy : GZA GeoEnvironmental, Inc. 2014).

50 Under Static Axial Compressive Load (2013). Load applied to the pile was measured using a load cell, and the jack pressure provided an indirect measurement of load. Displacement of the top of the pile was monitored with electronic displacement devices as well as with wireline devices read with an optical level. Load-displacement curves from the test piles are shown in Figure 34. Also shown on the graph of Figure 34 are lines representing the theoretical elastic deformation of each pile assuming no side resistance develops in the pile. For both test piles, the applied load was increased until it was at least three times the design load shown on the final plans from the original bridge construction. For the north abutment pile, “continuous jacking” was required to maintain the 120-kip load on the test pile. The consultant therefore suggested that the pile had achieved plunging failure. The final displace- ment of the north abutment pile was less than 0.6 inch. The south abutment load test reached a final load of 138 kips. The load-deflection data for the south abutment pile is relatively linear and never crosses the theoretical elastic compression line, although this is perhaps unsurprising for a timber pile in sand and potentially bearing on rock. However, the consultant notes that the load inferred from FIGURE 33 Static load testing of existing timber piles supporting the Haynesville Bridge (Courtesy: GZA GeoEnvironmental, Inc. 2014). FIGURE 34 Load-deflection curves from static pile load tests of existing Haynesville timber pile abutment foundations (based on data from GZA GeoEnvironmental, Inc. 2014).

51 the jack pressure was “significantly lower” than the load indicated by the load cell, which was used to develop Figure 34. Also, as described previously, wedges had to be used to remove the 19-inch segment from the south abutment test piles. Difficulties removing pile segments from loaded piles, interpreting load from the instrumentation, and working in low-overhead conditions are among the challenges that may occur frequently when load testing existing piles being considered for reuse. After completing the load tests, the free end of the test piles was re-connected to the top of the pile and pile cap using reinforcing bars before pouring concrete between the two pile segments. The abutment backfill was subsequently restored. The MaineDOT consultant recommended design values of axial geotechnical capacity based on the results of the load tests for the abutment piles and static pile evaluations for the pier piles. For the abutment piles, the final loads for each test pile were used as the nominal capacity for all piles at the respective abutment. A resistance factor of 0.7 was applied to the nominal capacity to account for the reduction in uncertainty produced by load testing. For the pier piles, the nominal capacity was predicted by means of a computer program that uses static analysis methods. Soil properties for the static analysis methods were derived from the MaineDOT subsurface information for the rehabilita- tion project. The agency used a higher resistance factor, 0.65, than typically used for static analysis methods, citing an observation that for the abutment piles predictions of nominal capacity from load test results and static analysis methods “correlate well.” MaineDOT also completed hydraulic and scour analysis of the Haynesville Bridge. Hydraulic analysis noted that the Federal Emergency Management Agency (FEMA) 100-year flood level is beneath the bridge. The agency’s scour analysis noted the bridge is not scour-critical and that the bridge has no history of scour issues. The scour analysis also included a comparison of the most recent bathymetric survey of the bridge with the existing bridge plans and observes a “small scour hole” near one of the piers. The lowest point of the streambed at the scour hole is approximately 3.25 feet below the elevation shown in the existing plans. The agency’s report qualifies the com- parison by noting that the “existing plans may not portray an extensive river survey.” The bottom of the scour hole is near the elevation of the top of the pile cap. The report recommends the scour hole “should just be monitored with routine underwater inspection” because of the “proven history” of the bridge piles. The report also recommends supplementing the riprap on the abutment slopes since the existing riprap is “small and sparse.” maineDot: lessons learned MaineDOT has implemented guidelines for foundation reuse that cover investigating existing foun- dations, determining load capacity, and making reuse decisions. The guidelines include more infor- mation regarding investigation of existing foundations than any of the other foundation reuse policies that were encountered during this Synthesis project. Although the investigation procedures include specific methods for different types of foundations (timber piles and granite abutments), the methods that are included in the guidelines vary in complexity and are not specifically prescribed. Rather, the guidelines emphasize that the selection of investigation methods be project-appropriate. During its agency interview, MaineDOT reported that existing foundation investigation techniques work most effectively when they are used in conjunction with one another for verification; the agency looks for the information from various investigation techniques to “converge.” The investigation of pile length for the U.S. Route 1 Bridge in Bath, Maine, through boring explorations, as-built plans and construc- tion diaries, and the parallel seismic method is an example of the agency’s multi-technique approach. Finally, the agency noted that during its interview that it had not observed any hesitation on behalf of the consultants with regard to recommending foundation reuse noting that as the owner, MaineDOT, exercises project-specific risk assessments when considering foundation reuse. illinois Department of transportation IDOT was an early adopter of a written foundation reuse policy, with a reuse procedure in place in the late 1980s. In the early 2000s, agency leadership decided to pursue a wider, more aggressive implementation of foundation reuse to reduce project costs for bridge replacement and modification

52 projects. The agency was confident that its foundation design practices had historically been inher- ently conservative. The conservatism provided technical justification for the agency’s reuse initiative, which included development of a more detailed foundation reuse policy. The policy was designed to achieve two primary objectives: (1) provide a basis for consistent reuse practice across all reuse projects and (2) establish a methodology for estimating current allowable capacity of driven piles from either values listed on old plans or, if available, construction driving records. The capacity meth- odology developed by the agency allows engineers to consistently and quantitatively take advantage of the foundation design conservatism. The agency reported that consultants typically would prefer construction of new foundation systems because of the legal risks associated with reuse. The agency suggested that the lack of national guidelines regarding foundation reuse makes consulting engineers hesitant to design foundation reuse projects. iDot foundation reuse policy: Bridge Condition Report Procedures & Practices IDOT’s policies related to foundation reuse are incorporated in the agency’s Bridge Condition Report Procedures & Practices (IDOT 2011). The manual outlines development of Bridge Condition Reports, which identify the current condition and function of a bridge and establish a scope of work for eventual bridge rehabilitation or replacement. It primarily addresses two topics: (1) bridge inspec- tion and (2) bridge analysis and scope of work selection. The inspection procedures are established in Section II of the manual, and the procedures reference six FHwA documents related to bridge inspection as well as the AASHTO Manual for Condition Evaluation of Bridges (1998). Section III of the manual addresses analysis and scope of work selection. The manual’s explanation of the bridge analysis process emphasizes judgment and consideration of available information. The bridge analysis process assists the engineer in determining the best scope of work for a given structure during the Bridge Condition Report preparation process. It applies thoroughness, sound judgment, and professional knowledge to the decision process. The analysis process requires the engineer to evaluate various aspects and components of the bridge to determine if they are suitable for reuse or repair. This begins with collecting the information necessary to make good evaluations and well informed decisions. Information gathered/determined by the engineer doing the analysis will include facts and well-founded assumptions. Once the analysis process is complete the results are reviewed in whole and the appropriate scope of work selected. The manual proceeds to summarize required evaluations: geometric and hydraulic capacity, deck, superstructure, substructure, miscellaneous checks, stage construction feasibility, and economic. It describes each evaluation, frequently referencing other agency documents containing more detailed procedures. Foundation reuse is addressed in the substructure evaluation portion of the manual. The foundation reuse policy outlines a procedure for estimating existing foundation capacity. The proce- dure is summarized here. iDot foundation reuse policy: Capacity Determination In the late 1980s, IDOT issued a foundation reuse policy outlining “abbreviated” and “detailed” reuse analysis methods. The abbreviated method indicated that reuse is allowed if the substructure is in good or repairable condition and the proposed dead load increase was less than 10% compared with the existing dead load imposed by the superstructure and substructure. The abbreviated method assumed that the live load would not change significantly and the increased dead load would result in settlement that was not noticeable and a minor decrease in factor of safety. If the proposed dead load increase was greater than 10%, the detailed method would be used. The detailed method required showing that the existing foundation capacity was greater than current (1980s and 1990s) AASHTO loading (then HS-20), with foundation capacity and factors of safety per the original foundation design, which was usually based on allowable stress design methods. In the early 2000s, the policy was updated to include greater predictions of existing foundation capacity. The policy update was motivated by the increased design live loads included in AASHTO’s LRFD bridge design specifications and a need to stretch construction funds; the agency considered the policy update justified by successful use of the old policy with no observed foundation reuse

53 problems. The outline for the updated policy is similar to the original policy, maintaining the use of abbreviated and detailed methods. The abbreviated method still requires a good or repairable condi- tion for the substructure; however, the updated policy specifically requires a condition rating of at least six. The updated policy’s abbreviated analysis allows increased dead loads of up to 15%, but the increase is calculated relative to only the superstructure (compared with both the superstructure and the substructure). The updated policy’s detailed method is required when the dead load increase is greater than 15%. For the detailed analysis method, new IDOT LRFD loads are compared with foundation capacity, which is calculated from the policy’s “Existing Spread Footing Capacity Deter- mination Table” and “Existing Pile Capacity Determination Table.” The tables are reproduced as Figures 35 and 36. The figures include the tables and accompanying examples as presented in the IDOT manual. The capacity of the existing shallow foundation is outlined in Figure 35. First, the designer checks the proposed load increase on the existing footing; if it is greater than 50%, reuse is not allowed. If the proposed increase is less than 50%, the allowable footing pressure is determined from the table shown in Figure 35, which consists of presumptive values based on the soil or rock type encountered below the footing in existing or new borings. The allowable footing pressures are based on allowable stress design and a factor of safety of 3.0. Therefore, equivalent factored resistance values can be determined by multiplying the values from the table by 3.0 to account for the factor of safety and then by an LRFD resistance factor of 0.5. If the resulting factored resistance is greater than the proposed loading reuse is allowed. A similar procedure is used for driven piles, but additional factors are used to increase capacity, accounting for various sources of conservatism. As for spread footings, reuse is not allowed when the proposed load increase is greater than 50%. The procedure defines the factored pile resistance, Rf, according to Equation 1: ( )( )= + + + + + +3 0.5 1 , Eq. 1R R C C H P P Sf e s b e e l m where 3 = existing ASD factor of safety, 0.5 = LRFD resistance factor, Re = existing capacity, and (1 + Cs + Cb + He + Pe + Pl + Sm) = capacity increase per table in Figure 36 If the factored pile resistance is greater than the factored pile loads, reuse is allowed. The increase in pile capacity established by the procedure accounts for six factors. Specific values for each of the factors are listed in the table in Figure 36, and IDOT’s explanation of each factor is listed here: 1. Source of information: Piles are installed to driving resistances greater than those listed on plans, making the value indicated on the plan drawings conservative. FIGURE 35 IDOT “Existing Spread Footing Capacity Determination Table” (IDOT 2011).

54 2. Dynamic formula bias: IDOT used the Engineering News Record (ENR) formula until 2007, when it began using the Gates formula. For typical agency hammer energy, the ENR formula under predicts pile capacity by 6% for piles with a capacity of less than 40 tons. 3. Hammer efficiency: Different hammer types deliver different energies even when their theo- retical energies are identical. Piles driven with high efficiency hammers (i.e., open-end diesel and air-steam) have more capacity than indicated. 4. Pile effect of hammer efficiency: Certain combinations of hammer and pile type result in greater transferred energy, which increases pile capacity. 5. Pile length: Longer piles have greater side surface area and greater opportunity for pile setup. 6. Mode of support: Depending on the ground conditions supporting the pile, additional increases are allowed to account for pile setup and/or low risk of settlement. scour and foundation reuse at iDot The Bridge Condition Report Procedures & Practices includes consideration of scour for bridges over streams being regarded for replacement: “If scour damage is identified or thought to be likely then repairs/countermeasures should be identified for bridges not being replaced.” Engineered riprap is the most commonly used scour countermeasure; however, the agency has also used driven sheet piles for construction purposes and then left them in place as countermeasures. IDOT has also used gabions, articulated blocks, and grouted riprap countermeasures. The agency performs hydraulic analysis according to HEC-18. Initial analyses typically assume sandy conditions at every site, in part because the soil gradation inputs that are required for hydrau- FIGURE 36 IDOT “Existing Pile Capacity Determination Table” (IDOT 2011).

55 lic models are generally not available when such models are developed. The agency reported that resulting scour predictions are typically severe, indicating scour depths as great as 40 feet below the mudline. The agency’s bridge manual (IDOT 2012) recommends reducing the HEC-18 scour depth based on material type as summarized in Table 14. notably, the agency’s bridge manual was published before the most recent version of HEC-18, which included updated scour predictions for various material types. iDot: lessons learned IDOT has a relatively long history of foundation reuse, which the agency promotes primarily as a cost saving measure. The agency developed and implemented a procedure for predicting the load capacity of existing foundations, which predicts greater capacity for driven piles than values listed on original plan drawings; the increased capacity helps agency engineers satisfy the increased live loading requirements that have been implemented in recent years. The procedure also helps ensure consistent practice from one reuse project to the next. The agency noted that consultants are leery of foundation reuse, preferring to recommend installation of new foundations because of legal risks associated with reuse. massaCHUsetts Department of transportation MassDOT frequently reuses bridge foundations. In 2011, the agency completed Fast 14, the notable reuse project summarized in chapter two. The agency’s survey response included estimated founda- tion reuse frequencies of five to ten times per year for bridge replacement and about once per year for bridge widening, bridge repurposing, seismic retrofit, and increasing clearance. Foundation reuse is consistent with the agency’s emphasis on maintaining and updating its existing infrastructure: based on estimates from the agency interview, approximately 90% of the agency’s budget for bridge con- struction is used for replacements and rehabilitations versus 10% for new construction. The agency’s LRFD Bridge Manual (MassDOT 2013) includes decision methodologies and eval- uation criteria that designers use to determine the scope of repairs and replacements required for each bridge project. The evaluation criteria are clear, but the manual affords agency engineers judgment to interpret the criteria. Its guidance regarding the top-level selection between bridge rehabilitation and bridge replacement is an example of such criteria: The Designer must first determine which project type will best achieve the goal [of a bridge project]. If both [repair and replacement] are equally viable, the Designer must then consider constructability of each project type, accident history, utilities, the constraints imposed by the feature crossed, and the constraints of traffic management. If both project types are still equal, then the Designer shall use the estimated construction cost as the deciding factor. The manual’s criteria for deciding between replacement and repair apply to all elements of the bridge, including foundations. The first version of the manual to acknowledge foundation reuse was published in 2005; the 2013 version includes more detailed information regarding structural, Soil/Rock Type Percent Reduction in HEC-18 Scour Depth Non-weathered limestone or dolomite 100 Shale or sandstone 90 Cohesive soil with unconfined compressive strength greater than 1.5 tsf 50 Cohesive soil with unconfined compressive strength between 0.5 and 1.5 tsf 25 Sands and cohesive soil with unconfined compressive strength less than 0.5 tsf 0 Source: IDOT (2012). tsf = tons per square foot. TABLE 14 IDOT POLICy REGARDInG SCOUR DEPTH

56 geotechnical, and hydraulic procedures related to reuse. Information about the agency’s experience with reuse, its evaluation criteria for reusing foundations, and examples from preliminary structures reports are presented in the following sections. motivations and Common applications for foundation reuse Foundation reuse is discussed in the preliminary, scoping phase of a bridge project, which is covered in Chapter 2 of the agency’s LRFD Bridge Manual. If the project does not involve major alignment changes, the agency will consider reusing the substructure to reduce project cost, satisfy right-of- way constraints, and improve constructability. The agency cited eliminating the needs for temporary shoring and large construction equipment as examples of improved constructability. For some proj- ects, foundation construction constraints are so severe that reuse is the only practical solution. The agency cited foundations adjacent to railroads, buildings, and other infrastructure as examples of such projects. For other projects, foundation reuse can be appealing because the risks are relatively low. Types of reuse projects with relatively low risk cited by the agency include: • Bridges on shallow foundations, which are easier to investigate than deep foundations; • Bridges with good construction records; and • Bridges not over water, which eliminates scour concerns. evaluation of foundations for reuse The first evaluation made by MassDOT when considering foundation reuse is the location of the piers. If there is no realignment, the agency will consider reuse. Second, the agency considers the state of the substructure using field observations and material testing (i.e., condition assessment). Chapter 2 of the agency’s LRFD Bridge Manual defines the goal for bridge rehabilitation projects as repairing a bridge structure so that it “can reasonably be expected to have its service life extended for a minimum of 75 years after the conclusion of construction.” Additional explanation of this determi- nation was provided in the agency interview. For concrete in the substructure, the agency typically bases its expectation of 75 years on determinations that concrete does not have any known problems resulting from freeze-thaw damage, alkali–silica reactions (ASR), or other sources of deterioration. The determinations are supported by field observations and material testing. Having found no known concrete deterioration, the agency expects that the concrete will not have any significant problems within 75 years and that any problems that do occur could be managed with general maintenance and preservation efforts. MassDOT’s condition assessment of the foundation portion of the substructure is more challeng- ing and involves historical records, field observations, material testing, and sometimes geophysical methods. Historical plans are consulted first to identify the type, location, and dimensions of existing foundations. The agency attempts to verify and supplement this information by excavating test pits adjacent to the foundation, taking core samples of concrete, and possibly using geophysical meth- ods. Geophysical methods are used when the other methods (test pits and coring) are inadequate for confirming structural integrity and capacity. The agency utilizes on-call contracts with consultants who specialize in geophysics. Typically, the specific geophysical method used is selected by the consultant to satisfy the specific information requirements for the project. The agency reported that the success of geophysics methods in identifying required information is mixed, but the geophysi- cal information is generally helpful. The agency also recommends testing soil resistivity to evaluate corrosion potential for reuse projects involving structures supported by steel piles. when the agency has considered reusing timber piles, it has evaluated the piles using test pit observations and installed monitoring wells to ensure piles are always submerged. The third evaluation for considering foundation reuse is the load capacity of the existing foun- dation. The agency reported that satisfying compatibility of the original foundation capacity with new AASHTO design loads is the most significant challenge it faces in reuse projects. The agency’s bridge manual states that bridge rehabilitation projects should be designed for HL-93 live loading, the current AASHTO standard. However, the manual includes exceptions for existing substructures

57 being considered for reuse, which can be considered using the HS-25 live loading from previous AASHTO standards. More lenient exceptions are also granted for reusing historical substructures. The evaluation process outlined above is documented in a Preliminary Structure Report (PSR). The contents of the report are outlined in the agency’s bridge manual: • Description of the existing bridge • Field survey of the existing structure • Material sampling and testing • Preliminary superstructure evaluation • Preliminary substructure evaluation • Geotechnical evaluation • Hydraulic evaluation • Cost estimate. Summaries of three recent example PSRs provided by MassDOT are presented in subsequent sections. Although the PSRs have been submitted for all three projects, construction of the bridge rehabilitation projects is still pending. scour and foundation reuse at massDot MassDOT requires a scour stability analysis for all bridge hydraulic studies. The first chapter in the agency’s LRFD Bridge Manual (2013) lists the reference manuals that should be used in hydraulic analysis, including HEC-18, HEC-20, and HEC-23, as well as HEC-25, Highways in the Coastal Environment (Douglass and Krolak 2008). Chapter 1 of the Manual also acknowledges the uncertainty of estimating scour depth and assigns responsibility to designers to “use sound engineering judgment to evaluate the reasonableness of any computed scour depth.” The Manual allows for modification of computed scour depths if clear documentation is provided. Finally, Chapter 1 establishes design flood return periods, which vary as a function of the structure’s functional significance. For bridge rehabilitation and superstructure replacement projects, Chapter 3 of MassDOT’s Bridge Manual requires that existing substructure be evaluated for its ability to withstand both a design and check scour event. Scour countermeasures are allowed where the existing substructures do not otherwise satisfy the design criteria. The agency’s Manual lists six allowable armoring counter- measures and four allowable structural countermeasures: • Flexible rock riprap revetments • Articulating concrete block systems • Grout-filled mattresses • Gabion mattresses • Partially grouted riprap • Grout/cement-filled bags • Concrete apron/curtain walls • Sheet or soldier pile/precast panel walls • Foundation footing underpinning (driven mini-piles through spread footings) • Construction of additional bridge spans or relief bridge/culverts. example psr: Bowker overpass over i-90, Csx railroad and ipswich street Bowker Overpass was constructed in the city of Boston in 1965. The structure is a four-span con- crete slab deck atop steel stringers supported by reinforced concrete piers. The bridge abutments and piers are all founded on steel pipe piles driven through Boston Blue Clay to bear on bedrock and then backfilled with concrete. In recent years, the bridge deck has had several emergency repairs, leading MassDOT to evaluate rehabilitation options. The PSR (Gill Engineering, Inc. 2015) docu- ments the evaluations, focusing on two critical decisions: (1) whether to replace the superstructure

58 using conventional construction methods or using ABC methods and (2) whether to replace the substructure, reuse it as-is, or reuse it with rehabilitations. For the first decision, the PSR recom- mends use of ABC methods based on the decision methodology outlined in Chapter 2 of MassDOT’s Bridge Manual. For the second decision, the PSR recommends substructure rehabilitation based on an extensive investigation that included foundation condition assessment, concrete integrity, and structural analysis. Historical documents for the bridge include as-built plans showing the installed pile lengths. Comparison of the installed pile lengths with information from new geotechnical borings confirm the piles are bearing on bedrock. The PSR also documents the results of excavating a test pit to examine the pile condition. The test pit and exposed piles are shown in Figure 37. The PSR notes minor sur- face corrosion; however, the measured diameter of the piles, 12.75 inches, matches the dimension shown on the as-built plans; therefore, the PSR concludes section loss is not measurable. In addition to the foundation condition, the PSR documents the investigation of the substructure concrete. Recent inspections rated the substructure condition fair (5), with scattered cracking, delam- ination, and spalling of the concrete. The PSR documents laboratory tests of concrete cores from the abutments, piers, and pile caps, including concrete compressive strength tests, petrographic analysis, and chloride content tests. The laboratory results generally indicated good concrete, although chlo- ride concrete is of concern: • The compressive strength values ranged from 3,100 psi to 7,400 psi. • Petrographic analysis revealed no signs of ASR, acceptable water-cement ratios, and proper air content. • Chloride contents ranged from 0.2 lb/cy to 14.4 lb/cy. The high end of the chloride content range is significantly greater than the threshold for corrosion of the reinforcement (American Concrete Institute 2001). The PSR notes that the limited spalling is evidence that corrosion of the reinforcement has likely not been initiated, but concludes that corro- sion is highly likely without rehabilitation. The PSR recommends that ECE be performed on the piers and pile caps to reduce the chloride content and extend the service life of the substructures. The PSR also documents preliminary structural analysis of the rehabilitated structure for HL-93 live loading. As a result, the report recommends adding a new structural face to the substructure after performing ECE to improve the axial and flexural capacity of the piers. Pile geotechnical capacity, assumed per AASHTO’s LRFD Bridge Design Specifications (2014) to be equal to the pile structural capacity since the piles bear on bedrock, is adequate. (a) (b) FIGURE 37 (a) Excavated test pit exposing the pile cap beneath one of the piers; (b) Top of one of the steel piles beneath the exposed pile cap (Source: Gill Engineering, Inc. 2015).

59 example psr: Hunt road over i-495 The bridge carrying Hunt Road over I-495 outside of Lowell, Massachusetts, was constructed in 1969. A PSR was prepared recently (McFarland & Johnson, Inc. 2015) to evaluate bridge reha- bilitation options. The bridge consists of a concrete deck atop steel beams resting on two concrete abutments and four multi-column concrete piers. The abutments are founded on 12-inch-diameter unreinforced cast-in-place concrete piles, and the piers are on spread footings. The PSR evaluates a proposed superstructure replacement, focusing on the feasibility of reusing the existing substructure. Reuse was investigated by reviewing historical documents, testing cores from the substructure con- crete, and performing structural analysis with updated loading. Historical documents include inspection reports, the most recent of which report that the piers are in fair (5) condition and the abutments in satisfactory (6) condition. Original plans for the bridge were located, but not as-built plans. The plans include boring information showing a thin layer of loam and peat over approximately 20 feet of sand. Twelve of the borings were terminated below the sand at “refusal;” the remaining four borings cored up to 5 feet of the rock noting only recovery values, which ranged from 15% to 46%. For the abutment foundations, the plans specify 40-ton, cast-in- place concrete piles with steel shells of unknown thickness. The “40-ton” descriptor is included in a title for the piling detail on the original plans; as described here; the PSR authors assumed that 40 tons was an allowable value. The pile lengths were not specified. The PSR assumes the piles were driven with a mandrel and omits any steel thickness in its analyses. For the pier foundations, the plans show one continuous footing beneath each pier. The plans include a crushed stone detail beneath the footings, presumably replacing the thin loam and peat layer. The plans note a maximum bearing pressure of 4,100 psf. Laboratory analysis of the cores revealed that the substructure concrete was in good condition. Compressive strength values averaged 5,600 psi. Petrographic analysis indicated no ASR and water- cement ratios between 0.4 and 0.47. Chloride contents were below 0.3 lb/cy in the piers and below 1.0 lb/cy in the abutments. Structural analysis of the abutments relied on allowable pile resistance values derived from the 40-ton value listed on the original plans. The PSR uses different allowable resistance values depend- ing on the loading situation being considered. For example, for LRFD (HL-93), the PSR multiplies 40 tons by an assumed original factor of safety of 6 and then applies the current AASHTO resistance factor of 0.10 for pile dynamic formulas to produce an allowable pile load of 32 tons, which was insufficient for the HL-93 loading. Similar analysis using AASHTO Load Factor Design practices with HS-25 loading also indicated insufficient pile capacity. Ultimately, the PSR recommended replac- ing the abutment backfill with lightweight geofoam to reduce dead load on the piles and satisfy the HS-25 scenario. Analysis of the pier footings indicated that the allowable bearing resistance listed on the plans is sufficient for all loading scenarios considered. The footings were recommended for reuse without modification. example psr: robertson street over i-93 The bridge carrying Robertson Street over I-93 in Quincy, Massachusetts, is a two-span, continu- ous, steel stringer bridge with a concrete deck built in 1958. A PSR was prepared recently (GPI, Inc. 2015) to evaluate bridge rehabilitation options. Foundations at the abutments were unknown. The original plan drawings included two options: (1) a gravity abutment without footings if a rock ledge was encountered during construction and (2) footings on soil if a rock ledge was not encoun- tered. The pier is on a continuous spread footing. Allowable bearing pressure values are listed on the original plan drawings and were used in structural analysis of the substructure, which revealed that the existing substructures were satisfactory for HL-93 loading. The analysis assumed the abut- ment foundations were on soil, not rock, reasoning this would be more conservative than the gravity abutment on rock. The PSR recommends replacement of the superstructure and reuse of the existing substructures based on the structural analysis results, the inspection ratings of the abutments (satis- factory, 6) and pier (fair, 5), and the historical performance of the foundations, for which no settlement had been documented. no field or laboratory investigations were completed.

60 massDot: lessons learned MassDOT reported more instances of foundation reuse than most other U.S. agencies. Foundation reuse is an important tool for MassDOT’s bridge program, which is focused on upgrading existing structures. Foundation reuse is considered for all existing bridge projects not involving realignment where a preliminary visual assessment indicated that the substructure is in relatively good condition. Constructability and economics are primary motivations for foundation reuse, which is more feasible for bridges on shallow foundations, bridges over land, and bridges with good documentation. Foun- dation reuse is allowed for bridges where scour countermeasures are required; however, the agency is generally less likely to reuse foundations for bridges over water. The agency’s evaluation of foundation reuse is generally conducted as part of a larger evaluation of reusing the entire substructure. The evaluation generally focuses on the condition of the substruc- ture and on structural analysis of the substructure according to more recent standards. Three example PSRs were reviewed and reveal varying levels of substructure and foundation investigation. Each example included considerable structural analysis, but condition assessment efforts varied widely. One PSR based its condition assessment on a review of historical documents without additional field data, whereas another PSR included a review of historical documents, evaluation of concrete cores in the laboratory, and excavation of a test pit to evaluate driven pile conditions. The agency explained that differences in the level of field investigation are based on bridge classification, engineering judg- ment, and site constraints, among other factors. missoUri Department of transportation Transportation funding trends experienced nationwide have been particularly challenging for Mis- souri DOT (MoDOT), an agency with the seventh largest highway system by miles (FHwA 2015b), the fifth lowest fuel taxes (American Petroleum Institute 2016), and no toll roads. To address rising upkeep costs for the large system during a period of declining revenues, the agency has emphasized innovative techniques to reduce individual project costs. Consistent with that emphasis, MoDOT has foundation reuse experience for many small bridges as well as several high-volume bridges crossing large rivers and lakes. The agency first began reusing foundations about ten years ago and there is a sense among the agency engineers interviewed that reuse frequency is increasing. The agency has no official policy documents regarding reuse; instead, reuse applications are considered for all exist- ing bridge projects, but investigations, decisions, and designs for reuse applications vary by project. Agency engineers reported that reuse guidance would be helpful, particularly if it were to address extending substructure service life. The agency’s approach to scour for reuse projects is presented here before highlighting projects where foundation reuse has been applied or considered. scour and foundation reuse at moDot In the late 1990s, MoDOT, in cooperation with FHwA, completed a hydraulic review of all agency bridges on the nBI and identified several hundred scour-critical bridges for which scour action plans were developed by the U.S. Geological Survey. The action plans require monitoring when stream or river levels reach a certain threshold and, for some bridges, closure of the roadway when stream or river levels reach a higher threshold. The scour action plans impact MoDOT foundation reuse deci- sions: if a bridge in need of rehabilitation has a scour action plan resulting in relatively frequent clo- sures, the agency is likely to replace the entire bridge rather than just the superstructure. For bridges with less onerous scour action plans, substructure reuse is considered. The agency will consider re using foundations for bridges with scour countermeasures; however, the countermeasures are typically implemented with contracts separate from the bridge work. Such arrangements generally result in cost savings because there is a wider pool of contractors capable of implementing the countermeasures. foundation reuse for small Bridges From the 1950s through the 1970s, MoDOT constructed several hundred low-volume bridges over small streams in rural Missouri using lightweight concrete decks designed for 25 years of service.

61 The substructures were constructed using normal weight concrete and were founded on rock with steel H-piles, spread footings, or timber piles. After 40 to 50 years of service, most of the superstruc- tures had deteriorated considerably, exposing the concrete reinforcement and requiring superstruc- ture replacement. Deterioration of the substructures was generally minimal, as determined by visual observation and hammer soundings. The agency estimated that 150 of the bridges remained in 2002, of which 73 are still in place. Foundations were reused for many of the replacements. Bridges on timber piles were an exception; unless timber piles are embedded in a cap below grade, the agency will not consider reusing timber piles because of the risk of decay resulting from exposure to wet-dry cycles. On paper, most of the reused substructures do not meet current MoDOT guidance for live loading; however, the agency considers the demonstrated performance of the bridges to be justifica- tion for reuse, particularly considering the lack of observed distress even in response to frequent loading by heavy farm equipment. The agency anticipates reusing the foundations for many of the upcoming superstructure replacements. i-44 over Gasconade river: Bridge slide over Unanticipated Karst The I-44 bridge over the Gasconade River was originally constructed in 1955 with a riveted plate girder superstructure. The 670-ft-long superstructure rested atop seven concrete piers founded on shallow foundations on rock. By 2011, the deck had deteriorated significantly and MoDOT decided to replace the superstructure with only minor repairs to the substructure, which was in considerably better shape than the superstructure. Because of the mobility consequences of interstate lane closures, MoDOT included a significant schedule incentive/disincentive in the project letting. The winning bid proposed constructing the new superstructure atop a new, temporary substructure adjacent to the existing structure, and then sliding the new superstructure from the temporary to the existing substruc- ture. However, upon installation of drilled shafts for the temporary substructure, karstic voids were encountered. MoDOT contracted a consultant to use geophysical methods to define the extent of the voids. Interpretation of five ER tomography profiles indicated that the size and extent of the voids were sufficiently small such that pressure grouting could reliably mitigate the risk of future collapse of the voids. After pressure grouting to fill the voids, construction resumed as proposed. Figure 38 is a photograph of the bridge slide, which was completed in one day by hydraulically jacking the new superstructure into place. The superstructure slid on Teflon bearing pads along a stainless steel plate connecting the two superstructures and lubricated with soap. Sliding the superstructure ultimately reduced the duration of lane closures from 60 to 20 days. The temporary substructure was left in place; MoDOT noted that it would consider reusing the substructure if the interstate is ever widened. Hurricane Deck Bridge: investigating old pneumatic Caissons and Cost-Based reuse Decisions The original Hurricane Deck Bridge was built to carry Highway 5 over the Osage Arm of the Lake of the Ozarks in the 1920s and 1930s. The original bridge, shown in Figure 39, consisted of an under-deck FIGURE 38 MoDOT contractor Emery Sapp & Sons, Inc. slides the new I-44 superstructure from a temporary substructure to the existing substructure over the Gasconade River [Courtesy : Emery Sapp & Sons, Inc. (Jones 2011)].

62 truss supported on massive pneumatic caissons keyed into bedrock. In 2012, MoDOT intended to replace the bridge but reuse the pneumatic caissons. Accordingly, the baseline design advertised by MoDOT involved four stages: 1. Build a temporary substructure on large-diameter, open-ended pipe piles adjacent to the exist- ing bridge. 2. Construct the replacement superstructure atop the temporary substructure. 3. Demolish the existing superstructure, with traffic rerouted onto the new structure during demolition. 4. Slide the new superstructure onto the existing caissons. To support the baseline design of foundation reuse, MoDOT and its consultants completed an investigation of the pneumatic caissons that was outlined by Axtell and Siegel (2014). The investiga- tion and its results are summarized in Table 15. The investigation revealed that the concrete caissons were in excellent condition. In addition to the baseline design, MoDOT allowed approved contractors to submit alternative technical concept bids that deviated from the advertised concept. Ultimately, one of the alternative concept bids was the low bid, edging out the lowest baseline bid by less than 1%. The winning con- cept involved replacing the existing bridge altogether with a new permanent structure on a different alignment and founded on drilled shafts. The alternative design achieved cost savings by using shorter spans and avoiding the need for temporary foundations and for sliding the new superstructure. FIGURE 39 Investigation of the original pneumatic caissons supporting the Hurricane Deck Bridge was completed by drilling from atop the old superstructure (Source: Axtell and Siegel 2014). Investigation Technique Details and Findings Historical records Caissons are massive concrete structures measuring 67 ft deep, 36 ft long, and 18 ft wide. The caissons are keyed 1 ft into bedrock. Core samples Two core runs were continuously sampled through each of the four caissons from the top of the caisson into the underlying bedrock. Recovery was generally greater than 90%. Compressive strength tests Tests of the core samples resulted in compressive strength values between 3,700 and 13,500 psi, with an average value of 7,400 psi. Petrography Petrographic analysis was performed on four concrete core samples. Average aggregate content of 71%, cementitious materials content of 29%, and air content less than 1%. Crosshole sonic logging Crosshole sonic logging was attempted between the two boreholes in each caisson. Results were inconclusive, likely because the distance between holes, 15 to 20 ft, was too great. Acoustic Tele- Viewer An Acoustic Tele-Viewer was used to visualize the sidewalls of the boreholes as shown in Figure 40. Details from Axtell and Siegel (2014). TABLE 15 EvALUATIOn OF ExISTInG PnEUMATIC CAISSOnS SUPPORTInG HURRICAnE DECK BRIDGE FIGURE 40 Acoustic Tele-Viewer results (Adapted from Axtell and Siegel 2014; Used with permission).

63 moDot: lessons learned For MoDOT, foundation reuse is an important cost-saving tool that has seen increased implemen- tation in the last ten years. The agency has several hundred bridges with scour action plans; those bridges are more likely to involve complete bridge replacement rather than reusing the foundations. The agency has found success reusing foundations for small bridges with superstructures that have deteriorated considerably more than the substructures. Foundations reused by the agency often do not satisfy current agency guidance for live loading; however, MoDOT considers the observed per- formance of the foundations evidence of their reliability. For reuse of foundations for larger bridges, the agency typically conducts more extensive field investigations of the foundations and the investi- gations are tailored to the unique conditions for each project. Project examples outlined previously included geophysical methods to evaluate risk from karst and an extensive investigation of massive, 80-year-old concrete caissons. Although the condition of the caissons appeared to be excellent, the agency decided against reuse because replacing the bridge along a new alignment was less costly. That particular project example serves as a reminder that foundation reuse is only one part of a com- plicated series of decisions to be made for bridge replacement projects. ColoraDo Department of transportation Colorado DOT (CDOT) frequently reuses foundations for bridge replacement, widening, and repur- posing. The agency’s reuse experience is particularly high compared with other western states. The agency explained that foundation reuse is often intended to minimize environmental impacts, which are associated with higher project costs. The environmental motivations and scour issues are pre- sented here. In its agency interview, CDOT reported several other noteworthy practices related to its foundation reuse experience: • The agency does not have formal policies or guidance related to reuse and noted that existing foundation details are typically limited since as-built documents are often not available and personnel associated with the original structure are frequently retired. • Investigation of existing substructures is generally limited to visual observations and hammer soundings for concrete integrity. The agency expressed some reservations over destructive methods such as concrete coring. For high-profile reuse projects, the agency has used consultants to conduct geophysical investigations. • Most reuse applications are designed in house. The agency reported that consultants are reluctant to design foundation reuse projects because the fee is not sufficient considering the amount of detailing work and “anxiety” resulting from liability issues. Consultants have designed some widening projects involving new foundations adjacent to existing foundations; however, for those projects the consultants strictly certify only the new foundations, not the original ones. • CDOT considers determining load capacity a chief obstacle for more widespread foundation reuse. The agency reported that structural engineers who manage bridge rehabilitation projects frequently need greater capacity values than the original design values to meet new live load requirements, but that agency geotechnical engineers are hesitant to assign greater values in the absence of new information. environmental motivations for foundation reuse In 1969, Colorado passed Senate Bill 40, which requires wildlife certification from the state’s Parks and wildlife agency for construction in any stream. CDOT’s Senate Bill 40 guidelines (CDOT 2013) require that “all practicable efforts shall be expended to avoid and minimize impacts to streams.” In addition, the guidelines require restoring stream profile, substrate, and habitat values to a condition “similar to or better than pre-project conditions.” On rehabilitation projects for bridges over streams, the wildlife certification requirements make foundation reuse appealing because reuse projects typi- cally have smaller construction footprints than full bridge replacement projects. For many such foundation reuse projects the agency prohibits contractors from working between bridge abutments, which avoids stream impacts.

64 The wildlife certification requirements have motivated foundation reuse for many small, rural bridges over streams. For such bridges, the abutments are often left in place when replacing the superstructure to avoid the need for construction activity in the stream. Although the abutments are left in place, new foundations are installed to support the new superstructure. The design for these applications assumes that the existing foundations support only the abutment loads, whereas the new foundations are designed to support the superstructure. Direct cost savings for foundations on the projects are likely limited, but the cost, time, administrative, and environmental benefits associated with avoiding construction activity in the stream are considerable. scour and foundation reuse at CDot Scour is a significant concern in Colorado because the state’s steep terrain and annual spring snow- melt are ideal conditions for flooding and high-flow velocities. The agency maintains a list of structures that it monitors for scour each spring during the snowmelt. volatile weather patterns are also cause for concern: rainfall in Boulder County in September 2013 was 18 inches compared with 1.6 inches on average. The resulting flooding damaged more than 120 CDOT bridges. CDOT’s Drainage Design Manual (2009) references HEC-18 and HEC-20 for scour consider- ations. The agency reported that foundations are reused when countermeasures are required. The Manual does not specify acceptable or unacceptable countermeasures. In its interview, the agency reported that riprap is typically employed as a countermeasure, but often the riprap washes away during a flood, after which the agency replaces the riprap. The agency also reported that structural engineers generally are responsible for selecting countermeasures. CDot: lessons learned Environmental regulations have motivated many of CDOT’s foundation reuse applications. The agency reported that consultants have been reluctant to design reuse projects because of legal risks and have refused to certify existing foundations for widening projects. Identifying the load capacity of existing foundations and, in particular, quantifying any increased capacity since original design, was identified as the agency’s main challenge for foundation reuse. The capacity challenge is linked to a lack of information regarding the existing foundations. As-built records are often unavailable, and investigation of the existing foundations is typically limited when foundations are reused for minor bridges. ontario ministry of transportation The Ontario Ministry of Transportation (MTO) Bridge Office advises and sets policies for the five regions within the province. One of four chief policy areas for the office is bridge rehabilitation, which includes foundation reuse. The agency’s survey response indicated that it reuses bridge foun- dations frequently, especially for widening projects, estimated at five to ten occurrences per year, and ABC projects, estimated at two to five occurrences per year. In its interview, the agency reported that many applications of reuse occur within MTO’s central region, where Toronto traffic congestion makes reducing mobility impacts an important consideration. Recently, the provincial government has nearly doubled short-term transportation investments; however, MTO staff levels and the size of the province’s transportation construction industry have remained nearly the same. In light of this disparity, bridge rehabilitations, including foundation reuse, are an appealing way to spend the investments and manage the agency’s bridge assets. foundation reuse procedures at mto: Decisions, investigations, and remaining service life Although MTO does not have formal policies or guidelines regarding foundation reuse, the agency explained that an informal procedure has evolved and is applied to most reuse projects. The agency first evaluates the load capacity of the existing foundation, comparing the value shown on original

65 design plans to the value required for the new structure to determine if additional foundation elements or other modifications would be required. Such modifications may deem reuse to be impractical. next, the agency performs condition assessment of the bridge substructure, including the founda- tion. Hammer soundings of exposed concrete are undertaken for all bridges. Concrete coring and tests of concrete compressive strength and chloride content are performed frequently, but not for all bridges. Half-cell surveys are also performed frequently. when half-cell survey or chloride content test results indicate a relatively high potential for corrosion, the agency has implemented mitigation practices including passive cathodic protection and chloride inhibitors. MTO also has excavated to expose abutment footings and pile caps as part of the condition assessment. In some circumstances, excavation of soil near the base of a pile cap has revealed severe corrosion of the tops of steel piles. In such circumstances, the agency frequently opts to replace the foundation system, although it considers encasing the tops of the piles in concrete if only a relatively short service life (e.g., 15 or 20 years) is needed for the rest of the structure. Considerations of required service life often play into MTO decisions regarding foundation reuse since the final decision is based on a life-cycle cost analysis. If the expected life-cycle cost of bridge rehabilitation (and foundation reuse) is within 20% of the expected life-cycle cost for bridge replacement, then MTO will opt for replacement. For complete superstructure replacement projects, the agency uses a 75-year target design service life. examples of foundation reuse at mto Two recent examples of foundation reuse are presented in this section. An additional example focus- ing primarily on scour aspects is included in the following section. MTO is currently completing the rehabilitation of the 17-span Bay of Quinte Skyway near St. Lawrence, Ontario. The bridge piers are on massive caissons keyed into bedrock. Reuse of the caissons was motivated by cost savings, environmental issues, and mobility constraints. Initial esti- mates indicated that replacing the substructure would double the project cost. In addition, the bridge serves more than 1,000 homes in the Tyendinaga Mohawk Territory, and closure would require an 18-mile detour. One drawback to reuse is that the substructure likely would not satisfy current seismic requirements. The agency reported that such tradeoffs are commonly encountered in reuse decisions and are considered on a case-by-case basis. Li et al. (2014) documented reuse and retrofit of foundations for the Mississagi River Bridge rehabilitation in 2012. The Mississagi River Bridge is a five-span, 390-ft-long bridge in northeastern Ontario originally constructed in 1943. Each of the four piers supporting the bridge was founded on a spread footing installed through sheet pile cofferdams, which were left in place and became part of the permanent foundation. The original bridge plans indicated that the footings were founded either on bedrock or native sand and gravel. Inspection of the bridge in 2010 revealed that many of the bridge elements were in poor condition, including a deteriorated deck, severe rusting of some structural steel members, corroded bearings, and loss of substructure concrete reinforcement result- ing from corrosion. In addition, underwater inspection and ultrasonic evaluation of the footings indicated loss of steel sheet pile section and spalling of the footing concrete at the mudline, as well as scour “to a depth below the underside of footing elevation at some piers.” Based on the results of a life-cycle cost analysis of rehabilitation options, MTO and its consultant decided on complete superstructure replacement and concrete encasement of the substructure com- ponents. Constraints associated with the location of the bridge within the Township of Iron Bridge were a significant consideration for the option of bridge replacement. As part of the rehabilitation planning, MTO and its consultant conducted a foundation investigation to gather further information about the condition and load capacity of the spread footings. The investigation consisted of coring through the bridge deck and each of the four spread footings into the material supporting the founda- tion. The investigation revealed that three of the four footings were founded on variable deposits of sand, gravel, and clay. In addition, core recovery in the same three footings was generally less than 15%. For the fourth footing, concrete core recovery was near 100%, and the footing was founded on bedrock. Structural analysis indicated that repair or replacement of the first three footings would be added to the scope of the rehabilitation project.

66 To address foundation concerns, MTO and its consultant considered replacing the entire bridge, enlarging the problematic footings and installing additional driven piles or drilled shafts, and under- pinning the problematic footings with micropiles. Of those, underpinning with micropiles was the only option that satisfied project schedule constraints, including mobility concerns, as well as envi- ronmental restrictions that permit in-water operations only during an approximately 50-day window each summer. Photographs of the micropile installation and construction of the system to transfer load from the existing piers to the new micropiles are shown in Figure 41. Figure 41 (a) shows the narrow ledge for micropile installation atop the existing footings; the left edge of the ledge is the sheet piles that were installed as cofferdam walls for the footing construction in 1943 and the right edge is the pier wall. The narrow ledge required installation of the micropiles through the deck of the existing bridge, which is shown in Figure 41 (b). The micropiles consisted of a 12-inch-diameter casing with Ties socketed through pier Beam between ties and micropiles Micropile heads (a) (b) (c) (d) FIGURE 41 Photographs of micropile underpinning of Mississagi River Bridge foundations: (a) narrow ledge atop existing foundations through which micropiles were installed, (b) installation of micropiles through bridge deck via casing through top of existing footing, (c) system for transferring load from existing piers to new micropiles (before concrete placement), and (d) completed piers with new concrete “jackets” (Source: Li et al. 2014).

67 a 2-inch-diameter center bar. The casings were installed through the existing foundations and 2 feet into bedrock, and the micropile bond zone extended 8 feet below the casing. Twenty-four micropiles were installed per pier. The system for transferring load from the existing piers to the new micropiles is shown in Figure 41 (c). Two types of structural members were installed through the piers by coring and then placing nonshrink grout. The first, railroad ties, were used at the top of the system and were selected in design because of compactness and availability. The second, high-strength steel bars were used at the bottom of the system. The ends of the railroad ties rest on a load transfer beam that rests on the micropile heads. After forming and pouring concrete for the load transfer system, the piers were jacketed with concrete, as shown in Figure 41 (d). In addition, riprap was placed at the base of the foundations as a scour countermeasure. The design of the micropile foundations included lateral resistance from the overburden material. Construction of the micropile underpinning was completed in time for the overall bridge reha- bilitation to be completed on schedule. However, project costs were considerable and exceeded the estimated construction cost for complete bridge replacement. As noted previously, environmental and mobility constraints would have complicated complete bridge replacement. scour and foundation reuse at mto The Canadian Highway Bridge Design Code (CSA Group 2014) requires that scour be estimated for all structures. The Code references the Transportation Association of Canada’s Guide to Bridge Hydraulics (2004) for analysis procedures. Foundation reuse is not prohibited in cases where scour countermeasures are required; however, MTO reported in its interview that for such cases the cost of implementing countermeasures often leads to decisions to install a deeper replacement foundation. Scour recently affected rehabilitation of the Rosseau River Bridge in Rosseau, Ontario. The origi- nal bridge was constructed in the 1930s as a single-span bridge on spread footings. Subsurface conditions at the site consist of up to 50 feet of sands and gravel above bedrock. The bridge has been widened several times in its history, including a 1982 superstructure replacement. In 2015, a contractor working on a rehabilitation of the bridge discovered a large void under the west abutment footings, presumably the result of scour. The bridge was closed immediately and a temporary detour bridge was installed for use during construction of a permanent replacement. A photograph of the bridge substructure during the closure is shown as Figure 42. The permanent replacement bridge is also a single-span structure on shallow foundations, but twice as long as the original bridge to reduce the risk of scour by moving the foundations away from the river. The agency reported in its interview FIGURE 42 Temporary support beneath the old Rosseau River Bridge (From exp Services Inc. 2016).

68 that one lesson learned from the Rosseau River Bridge replacement was that underwater inspection of the footings should have been performed as part of the condition assessment supporting the 1982 superstructure replacement as well as for the 2015 planned rehabilitation. mto: lessons learned The experience of MTO with foundation reuse is similar to that of U.S. agencies with significant experience reusing foundations. MTO applications of foundation reuse are frequently driven by urban congestion. MTO does not have formal policies or guidance related to foundation reuse; how- ever, an informal process has evolved that involves considering load capacity, evaluating substruc- ture condition within the context of required service life, and ultimately the cost of reuse versus replacement based on a life-cycle cost analysis. The agency reported that estimating remaining ser- vice life is the biggest challenge of foundation reuse and that its most significant lesson learned regarding foundation reuse was to perform sufficient investigations before implementing foundation reuse projects because “surprises are expensive.” lessons learneD from all Case examples Experiences of the six agencies described in this chapter vary substantially, but each provides valu- able lessons regarding foundation reuse: • For most case example agencies, project cost savings are the primary motivation for reusing bridge foundations. • Although cost savings generally prompt reuse decisions, project-specific constraints were reported to leave agencies with few options other than reuse for many projects. Environmental regulation is one such constraint, particularly when foundation replacement would impact streams or wetlands. Constructability, especially when working near existing buildings, historical struc- tures, or railways, is also a constraint associated with reuse. • Practices related to investigation of existing foundations vary widely, not just among the case example agencies but also within each agency’s experience with reuse. Reported applications of foundation reuse for larger, heavily trafficked bridges often included more advanced methods, including geophysical methods, whereas applications for smaller bridges frequently had only visual investigations. • Three of the case example agencies, MaineDOT, IDOT, and MassDOT, address foundation reuse in agency guidance. MaineDOT’s guidance outlines recommended investigation procedures for different types of foundations without explicitly requiring that any specific investigation methods be applied. IDOT’s guidance focuses on load capacity prediction. MassDOT’s consider- ation of foundation reuse is part of a larger agency evaluation process for bridge rehabilitations. MassDOT’s reporting requirements for preliminary evaluations of existing bridge options require field visit data, material testing, and structural analysis. Several sections in MassDOT’s policy include statements supporting the application of engineering judgement to decision making and policy interpretation. • All case example agencies discussed challenges associated with predicting capacity of existing foundations, particularly with respect to the increased capacities necessary to satisfy updated live load requirements. Two of the agencies identified capacity prediction as the primary obstacle to foundation reuse and another agency, IDOT, developed a reuse policy largely in response to the capacity challenge. • The agencies without capacity prediction methods all expressed some degree of willingness to rely on observed, historical performance as justification for reuse when current design criteria could not be satisfied using original capacity values. • Scour considerations are another challenge reported by case example agencies. The agencies were generally less likely to reuse foundations when scour was a possibility, resulting in more applications of reuse over land than water. Agency interviews revealed a general perception that scour prediction methods are rather conservative, and perhaps overly conservative. • IDOT and CDOT reported that consulting engineers are generally wary of designing foundation reuse projects because of legal risks. In contrast, MaineDOT reported no hesitation on behalf

69 of recommending reuse, and MaineDOT, MassDOT, and MTO provided example projects that were designed by consultants. The resulting picture of consulting practice for foundation reuse projects is unclear, but it appears likely that the uncertain standard of care noted in the litera- ture review (Brown 2014) makes at least some consulting engineers hesitant to design reuse projects. • In general, the agency interviews confirmed foundation reuse to be a multidisciplinary effort. For most case example agencies, the effort is led by structural engineers, but requires critical input from geotechnical and hydraulic engineers. The difference in perspective among disciplines was also apparent from the interviews. For instance, one structural engineer described geotechnical engineers as “timid” with respect to assigning load capacity values, while a geotechnical engi- neer (from a different agency) lamented that structural engineers were “always wanting definite numbers.”