Design and Load Testing of Large Diameter Open-Ended Driven Piles (2015)

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24 chapter three AGENCY STATE OF PRACTICE FOR LARGE DIAMETER OPEN-ENDED PILES This chapter provides detailed findings on how transpor- tation agencies view and use LDOEPS based on the survey results and follow-up interviews. Some information from the literature review is also included. INTRODUCTION To understand the perspectives and current practices of state agencies, an on-line survey was used to determine which agen- cies have experience with LDOEPs and to gather some prelimi- nary information on how these piles are used by those agencies that currently use them. The goal of the survey was to identify those state agencies with experience using LDOEPs, obtain basic information on their design and construction techniques, and identify those that would be willing to provide detailed experiences through one-on-one interviews. Appendix A con- tains the survey. The geotechnical engineers (or equivalent) in all 50 state DOTs plus the District of Columbia and Puerto Rico were invited to complete the survey. Of the 52 agencies surveyed, 44 (85%) provided responses. Figure 9 is a map of the responses, with green indicating states that have experience with LDOEPs, red states that do not use LDOEPs, and gray states that did not response to the survey. The survey was structured such that the first question asked if the agency had experience within the last 10 years or cur- rently uses LDOEPs. If the agency answered “No,” the respon- dent was able to provide information on why LDOEPs are not used by the agency before jumping to the end of the survey. This allowed for the collection of reasons why LDOEPs are not used for inclusion and discussion in this report, as well as easier analysis of the answers provided by agencies that do use LDOEPs. Of the 44 agencies that completed the survey, 18 (41%) indicated that they had experience with LDOEPs. Of this group of 18, two agencies [Maine DOT and North Carolina DOT (NCDOT)] reported that they are in the design phase of current projects where they are considering using LDOEPs, but have little to no past experience with LDOEPs. Most of the remain- ing agencies in this group have limited experience on only a few projects within the last 10 years. Some may have also had a few structures on these piles built predating the 10-year time frame. Appendix B contains a summary report that focuses on the responses of the 16 agencies actively using LDOEPs. Two agencies, the Maine and North Carolina DOTs are only in the design stages of projects with LDOEPs and are not included in the summary report. Graphs and charts of the responses to questions with “Yes/No” or multiple choice answers are pro- vided. Questions with written answers are shown in table form. It was believed that having “no answer” data in the totals would not be an accurate reflection of the state of practice. To acquire more detail on the experiences of this group, telephone interviews were conducted with seven of the 16 agencies. The agencies with the most experience were selected to capture the range of experiences these agencies have with respect to pile types, sizes, and soil conditions. The notes from the telephone interviews are included in Appendix C. AGENCIES NOT USING LARGE DIAMETER OPEN-ENDED PILES Twenty-six of the 44 agencies that responded to the survey (59%) indicated that they do not consider the use of or have not used LDOEPs for transportation structures. The survey provided the opportunity for respondents to provide comments on why their agency does not consider or use these piles. These responses could be grouped as follows: • The agency responded simply that they do not use LDOEPs or did not provide any additional comment. • The agency is evaluating LDOEPs for a project, but has not yet used them. • LDOEPs are not cost-competitive with other deep foun- dation systems. • Geologic and soil conditions are not suitable for LDOEPs, but more suited to drilled shafts, H-piles, or smaller diameter piles. • There is a lack of expertise and equipment among the pool of contractors that typically perform foundation installation in the state. • Smaller pile sizes are suitable for the typical structure size and loads. • Design of these piles is not specifically addressed in AASHTO Design Specifications, leading to uncertainty in extrapolating the standard AASHTO axial resistance

25 prediction methods to larger pile sizes. Specific design issues and questions include: – Prediction and extent of plugging, – Determination of pile capacity/resistance, – Length of concrete infill, – Structural design of concrete–steel section, and – Resistance factor selection. • Concerns over vibrations to adjacent structures. • How to evaluate potential benefits against uncertain con- struction costs and risks. The comments and concerns on design issues, as well as the benefits versus construction costs and risks, reflect some of the reasoning behind the undertaking of this syn- thesis project. The comments about unsuitable soil condi- tions, poor cost-competitiveness, and a lack of experienced contractors are related and are to be expected for some areas of the country. Not all locations are suitable for every foundation type. SURVEY RESPONSES Agencies That Responded The 16 agencies that indicated they currently use LDOEPs are listed here. These agencies are spread across the coun- try and represent a wide range of subsurface and geologic conditions. The level of experience is generally low, with all but Alaska Department of Transportation and Public Facili- ties (ADOTPF) and California DOT (Caltrans) noting that they have implemented no more than ten projects utilizing LDOEPs within the last ten years. Those agencies both noted that they have executed more than 50 projects with LDOEPs in the last ten years. Alabama (ALDOT) Louisiana (LADOTD) Alaska (ADOTPF) Maryland DOT California (Caltrans) Massachusetts (MassDOT) Florida (FDOT) Minnesota (MnDOT) Idaho (ITD) New York (NYSDOT) IDOT Ohio (ODOT) Iowa DOT Texas (TxDOT) Kentucky (KYTC) Virginia DOT (VDOT) Each of these agencies reported that they use design con- sultants for LDOEPs. In addition to using consultants, most of the 16 said they also used one of the other three forms of design delivery: design by agency (75%), design-build (75%), and value engineering change proposal (VECP) by contractor (69%). Applications, Selection, and Pile Types Applications/Selection Several choices were provided to respondents to indicate the reasons that LDOEPs were selected for projects in their area, with respondents allowed to select more than one answer. The most common response (94%) was to resist large lateral loads. Slightly more than half also chose large axial loads (56%) and soil and rock conditions (56%). Cost-benefits (31%), special applications (25%), and other (19%) were also selected. Sched- ule and environmental considerations were given as “other.” Figure 10 illustrates the reasons for selecting LDOEPs. FIGURE 9 Map of survey responses.

26 Common themes in the interviews were the ability to resist large lateral loads and the potential to avoid cofferdams and excavations for pile footings. By taking advantage of the effi- cient bending resistance of LDOEPs, a few larger piles can be used in a pile bent, eliminating the need for a pile footing and the associated cofferdam when using a large number of smaller piles. Also, fewer piles were reported to have construc- tion schedule benefits and occasional environmental benefits. Selection of LDOEPs is often heavily influenced by local practice—the availability of the piles and a qualified con- tractor pool that is capable of installing LDOEPs. Areas that have subsurface conditions favorable for LDOEPs tend to have piles readily available and experienced contractors to install them, making them a viable choice of foundation. Areas not as favorable tend to lack contractors experienced in LDOEP installation, making them less attractive to agen- cies to consider. Where LDOEPs are typically used, the process of evaluat- ing and selecting LDOEPs over an alternate foundation type is part of the typical bridge design process. The foundation that is ultimately selected is chosen based on many factors that usually include suitability of the foundation type for the specific project, costs, performance, and schedule. ADOTPF specifically noted several additional benefits with LDOEPs that help with the selection process, including: • Less environmental impact—pile bents with a few LDOEPs remove the need for excavation and cof- ferdams for large pile footings containing numerous H-piles or small pipe piles. • Quick installation—ADOTPF is utilizing accelerated bridge construction as a result of the very short con- struction season in Alaska. There are also time restric- tions because of the prevalence of wildlife. Fewer large piles can be installed more quickly and superstructure work started sooner. • Seismic design—a benefit of adopting 48-in. pipe piles has been that no major changes are needed to designs to meet updated codes, since the pipe piles are suitable for the updated loadings. Concrete Piles Seven agencies use concrete LDOEPs, with five using spun- cast post-tensioned piles, one bed-cast piles, and one using both. The diameters range from 36 to 66 in., with 36 in. and 54 in. being the most common. Wall thickness ranges from 4 to 8 in., with concrete compressive strengths ranging from 6 to 7 ksi. Prestress values were reported to range from 0.7 to 1.6 ksi. Steel Piles Twelve agencies utilize steel LDOEPs with a variety of welded plate, straight seam welded, and spiralwelded pipes. The reported diameters ranged from 36 to 96 in., with 36 to 48 in., being the most common. Wall thickness values were ½ in. to 2 in., with yield strengths ranging from 36 to 75 ksi. Grade 50 steel appears to be the most typical. Standard Plans and Specifications Very few agencies (5) indicated that they have any standard plans or specifications for LDOEPs; most use their published standard specifications written for driven piles without regard to size. Some of the “Yes” answers were followed with descrip- tions of special provisions or modifications (such as reinforce- ment of testing requirements) rather than a completely separate specification. FDOT has settled on a standard design for two FIGURE 10 Primary reasons for selecting LDOEPs.

27 types of concrete LDOEP: a 54-in.-diameter spun-cast post- tensioned pile and a 60-in.-diameter full-length pre-tensioned bed-cast pile. NYSDOT also has a standard specification for concrete cylinder piles that can be modified, if necessary, for each project. Design Piles Bearing in Soil To determine the methods used by agencies for determining static axial resistance and displacements, several common methods were listed for both cohesionless and cohesive soils. Respondents were asked to select all methods that they use and were provided an option to explain any “in-house” or other methods in use. The methods for both soil types are shown in Figures 11 and 12, with the percentage of the 16 agencies that selected each. The Nordlund and the alpha (Tomlinson) methods are the most often cited for cohesionless and cohe- sive soils, respectively. The “Other” and “In-House” methods included several items that are discussed here. Louisiana Department of Transportation and Development (LADOTD), MnDOT, and NYSDOT all indicated that they generally follow the FHWA methods with little or no modifi- cation. MnDOT noted that most of its experience, however, FIGURE 11 Static analysis methods in cohesionless soils. FIGURE 12 Static analysis methods in cohesive soils.

28 has been to drive pile to bear on rock, so that calculations of side resistance are not a significant issue for static resistance. NYSDOT noted that they temper the FHWA methods with their dynamic test experiences at other sites. VDOT reported that consultants on design-build projects are not limited to the method they can select and so can use methods other than those listed in the survey. Several agencies reported that they have developed in-house methods for estimating pile axial resistance including Alabama DOT (ALDOT), ADOTPF, FDOT, Illinois DOT (IDOT), and (TxDOT). All of the methods apply correlations to historical installation data, primarily on small diameter piles. ALDOT has an in-house computer program developed from test pile data performed in the 1960s and 1970s (K. Davis, personal communication with R. Thompson, July 2014). The program was originally written in Quick Basic to perform on DOS computers, but was recently upgraded to a Windows- based version. The program initially only accounted for ulti- mate tip and side resistance in sand and clay soils; it lacked the modeling of silty soil and the calculation of pile settlement. The latest version now has silty soil models and calculations of pile settlement, as well as the ability to perform calculations utilizing an LRFD resistance factor. The initial program was based on test pile data performed during the construction of the I-65 bridges through the river delta in Mobile County and the following references: • NAVFAC DM-7, Soil Mechanics, Foundations, & Earth Structures, p. 7-13-9. • U.S. Steel Highway Structures Design Handbook, Vol. 1, p. 1/10.10. • Peck, Hanson, and Thornburn, Foundation Engineering. • Highway Research Record, No. 333, p. 93. ADOTPF has developed a modified beta method using case studies from historic PDA®/CAPWAP® results (Dickenson 2012). The study is based on 20 years of driving records and PDA® data for 36 to 48 in. LDOEPs in granular, cohesionless soils. This method uses region-specific empirical relationships to estimate unit side and base resistance, with an equivalent plug used for base resistance calculations. The methods have been used for some recent projects (2013 and 2014), where the dynamic test results matched very well with the modified static calculations. A summary of the report is included in chapter five. Prior to using this method, ADOTPF applied the unmodi- fied FHWA methods as contained in the computer programs DRIVEN and Allpile. It believed that these methods were not modeling the plug correctly and that the methods were not properly “scaling up” for larger pile sizes; that is, the unmodi- fied methods were based on smaller pile sizes that were not adequately modeling soil–pile behavior for larger pile sizes. FDOT typically uses the computer program FBDEEP devel- oped by the University of Florida for the agency, but avail- able commercially through the Bridge Software Institute. The program allows for the use of either SPT or CPT data for pile design, with the SPT methodology based on empirical correla- tions between CPT and SPT tests for typical Florida soil types. The correlations are based on pile installations in Florida. Some consultants and others outside the state of Florida use FBDEEP for foundation design. IDOT uses an in-house design method designated the Mod- ified IDOT Static Method (IDOT 2011). The original IDOT static method was developed more than 40 years ago, correlat- ing allowable pile resistance to the ENR (Engineering News Record) dynamic formula. In 2007, the method was updated to reflect the change to LRFD design, producing the Modified IDOT Static Method. The nominal pile resistance is calculated from unit side and base resistance that include correction fac- tors for cohesive or noncohesive soils. The nominal unit side and tip resistance are both calculated from correlations to SPT N(1)60 values for cohesionless soils and undrained shear strength, qu, for cohesive soils. Factored resistance is calculated using a Geotechnical Resistance Factor, jG, of 0.55 applied to the nominal pile resistance, less reductions for liquefaction, scour, and downdrag. TxDOT has design methods based on the Texas Cone Penetrometer (TCP) that is the standard in situ test method for TxDOT instead of the SPT or CPT. (Texas Department of Transportation 2012). The TCP is a cone similar to the CPT driven with a hammer similar to the SPT. The TCP blow counts, NTCP, are used indirectly to estimate the in situ, undrained shear strength of soils. Correlations of NTCP to pile tip and side resistance are used for pile design. The cor- relations were initially developed in the 1950s and have been updated periodically (Vipulanandan et al. 2008). The data used for the correlations include piles of up to 24 in. in diameter. The correlations for pile design are presented in the TxDOT Geotechnical Manual as design charts plotting “Allowable Skin Friction” or “Allowable Point Bearing” versus NTCP. The different relationships are plotted for basic soil types. The plots include limiting values of maximum values of side and tip resistance for design. Two agencies mentioned that they use the API design methods in API RP2 GEO (2011). Caltrans uses this method regularly; KYTC used this design guidance for the single project it has under design for which a load test program was performed (Terracon 2014). During the telephone interviews, one of the KYTC consultants noted that his experience, and that of the offshore industry, indicates very good agreement of API RP2 GEO with load test data. Significant differences between the API and FHWA methods that are beneficial when using the API method are: • API evaluates friction inside of pile plug formation, rather than a more arbitrary selection by FHWA. • API limits side resistance to a maximum mobilized value, whereas FHWA (Nordlund) does not include an upper limit by default.

29 KYTC noted that the soil properties and limiting values of pile resistance recommended or determined by the API method were adjusted based on KYTC and Terracon experi- ence and the CPT data collected for the project. The CPT data were especially helpful in evaluating limits on mobi- lized pile resistance. Piles Bearing on Rock Six of the 16 agencies using LDOEPs drive the piles to bear on rock; four do not typically use special toe treatments, one does use special toe treatments, and one does either depend- ing on the rock formation. The treatments tend to be strength- ened rings or other special reinforcement added to the toe. ADOTPF has some special cases where if lateral support is needed the rock is cored to seat the pile in the socket. Con- crete is sometimes used to set the pile. For the design of rock-bearing piles, most agencies design based on the structural limits of the pile section and use wave equation analyses. The piles are monitored during driving with PDA® or driven to a required blow count. FDOT utilizes FBDEEP® with its method for soft Florida limestone. MnDOT made special note that while static resistance analysis methods are reasonable estimates of the long-term resistance of the pile the resistance is not always easily dem- onstrated with dynamic testing methods. There is also concern with appropriate modelling of the pile and proper selection of associated damping/quake needed for analysis, considering the general low level of experience with dynamic testing of LDOEPs compared with smaller pile diameters. Resistance Factors Most of the agencies using LDOEPs utilize the resistance factors for driven pile design recommended in the current AASHTO Specifications, as noted in Figure 13. Eight agen- cies (50%) stated they use the AASHTO factors, whereas five (31%) use a combination of AASHTO and agency-specific fac- tors for driven piles in general. Three agencies (19%) indicated that they use something other than AASHTO resistance fac- tors. Caltrans uses factors that they have developed. ALDOT is currently evaluating resistance factors for LDOEPs as it does not have any projects in design since LRFD implementa- tion. TxDOT’s design method uses the TCP as an Allowable Stress Design-based method. Pile Plugging Most agencies (10) evaluate the potential for pile plugging during driving on a site basis, looking at the specific soil con- ditions, pile type, and pile size. Of the remaining six agencies, three [Idaho TD (ITD), Iowa DOT (Iowa DOT), and IDOT] usually assume that a plug will form, whereas the remaining three [FDOT, Maryland SHA (MSHA), and TxDOT] assume that the plug will not form. Note that the three “assume will form” agencies have had limited numbers of pile installations, including ITD having only one use of LDOEPs. FDOT’s basis for assuming that a plug will not form is from research on concrete cylinder piles by McVay et al. (2004). FDOT also had undertaken direct observations on two projects where the soil and water column inside the pile rose in the pile during driving, causing problems with pile cracking owing to increased stress from pressure inside the pile. A more detailed discussion of these occurrences is included in chapter five— Case Histories. For KYTC’s only LDOEP project to date plugging was not anticipated; therefore, the use of a constrictor plate in the pile was investigated in order to facilitate plug development in a specific target stratum (Terracon 2014). The key question was development of the plug—if the plug is being relied on to either achieve penetration into the target stratum or to achieve the nominal pile resistance, how could the certainty of the plug developing and its location be determined? Some of the test piles were fitted with steel constrictor plates inside the pile to encourage plug development. The evaluation started with the API method internal and external skin friction analyses, com- pared with a plug forming to determine the most effective point to set the plate to engage the plug. For the test piles, the plate was set at an elevation higher than estimated in order to have the piles penetrate further into the target stratum than determined for the design. This was done to account for variability of the top of the target stratum and to provide confidence that the piles did bear in the stratum. Of the two pile diameters evaluated, the 48-in.-diameter piles tended to develop a plugged condition at the target stratum, while the larger 72-in.-diameter piles did not. Additional discussion of the test program is included in chapter five—Case Histories. FIGURE 13 Source of resistance factors.

30 Setup and Relaxation Twelve of the 16 agencies (75%) evaluate setup and relax- ation for each project, although most assume that relaxation will not occur. Dynamic testing on restrikes of piles is very common to evaluate or demonstrate that setup has occurred. VDOT stated that the coastal areas of Virginia routinely exhibit 200% to 300% setup. Production pile lengths are set based on a test pile program documenting the setup. High- strain dynamic tests with restrikes have significantly reduced the pile lengths being installed compared with when setup was not determined and accounted for. Drivability and Driving Criteria All 16 agencies typically use wave equation analysis to assess drivability, although not all utilize it during design as part of the pile selection process. Some, such as MnDOT, will per- form an initial check during design for larger diameters and special conditions (such as needing to penetrate a hard layer to get to minimum tip), where high driving stresses are antic- ipated to verify that the designed piles can be installed by using typical hammers. Most typically rely on the contrac- tors’ submittals to evaluate drivability for the specific hammer system and pile design. NYSDOT will evaluate drivability during design, including various plugging scenarios, as part of the drivability evaluation. The use of test piles to evalu- ate drivability was also noted by IDOT and MassDOT. IDOT includes comparison of the test pile to the WSDOT driving formula. ADOTPF does not typically do full drivability analysis during design for most loading conditions, but will review driving stresses with low penetration as well as with pen- etration at the estimated tip. If a specific project has very high axial loads, or high driving stresses are anticipated, a wave equation analysis will be performed to verify that the designed piles can be installed with the use of typical hammers. Contractors are required to submit wave equa- tion analysis with equipment submittal as is typical with most agencies. Figure 14 shows the agency responses to the question con- cerning driving criteria. The use of high-strain dynamic tests on test or indicator piles for setting driving criteria is used by 12 of the 16 agencies (75%). Verification of the required resis- tance with restrikes is also common [10 of 16 (63%)]. Load tests and wave equation analyses were used by almost half of the agencies [7 of 16 (44%)]. Driving to a specified tip ele- vation (routine practice for LADOTD) to practical refusal or to a specified resistance using wave equation analyses are also used to some degree among the agencies using LDOEPs. All of these agencies contributed to NCHRP Synthesis 418: Devel- oping Production Pile Driving Criteria from Test Pile Data (Brown and Thompson 2011). Details on how each develops and uses driving criteria can be found in that report. Testing Most of the 16 agencies use high-strain dynamic testing to measure or demonstrate pile resistance, as well as to monitor driving stresses to reduce pile damage. Some use it exclusively (e.g., ADOTPF), whereas others use it alone or with rapid and/or static load tests (e.g., FDOT). Most use restrikes to develop setup curves and establish driving criteria (e.g., LADOTD). VDOT noted that all projects with LDOEPs will have a com- prehensive test program of high-strain dynamic testing during driving, often supplemented with static or rapid load tests. FIGURE 14 Driving criteria practices.

31 FDOT relies heavily on dynamic testing to verify resistance, set tip elevations, and establish final order lengths. The agency has had no significant issues with dynamic testing; however, load test programs did indicate that pile resistance deter- mined by CAPWAP® was conservative compared with static/ Statnamic® testing (Muchard 2005; Kemp and Muchard 2007). The test program on steel LDOEPs executed by KYTC (Terracon 2014; see also chapter five—Case Histories) included an extensive program of dynamic, static axial, Statnamic® axial, and Statnamic® lateral tests on piles with wall thicknesses ranging from 1 to 2 in. KYTC concluded that dynamic testing was underestimating the static pile resistance as determined by the static and Statnamic® tests. In addition to comparisons of test methods, a detailed eval- uation of dynamic pile testing records was done to consider methods of improving the match quality and the estima- tion of static pile resistance when considering plugging. Comparisons of analyses using a single-toe pile model and a double-toe model were made, as well as application of radial or radiation damping models. Among other findings, it appeared that the radiation damping models provided better match quality as well as estimating base resistance when the constrictor plates were engaged. MnDOT considers problems with demonstrating the required pile resistance by means of dynamic testing meth- ods to be a significant issue. There is reluctance by MnDOT, as with many other state DOTs, to use a higher resistance than can be verified though testing. The experience of MnDOT has been that it is often difficult to provide a large enough hammer to move the pile enough on restrike to dem- onstrate the required resistance once the pile is firmly bear- ing on rock or any setup has occurred. Having adopted the approach to perform rapid load tests (Statnamic®) to better assess the static pile resistance and help correlate and/or cali- brate PDA® data has resulted in more confidence in designs utilizing LDOEPs. NYSDOT used a combination of static and dynamic load tests 25 to 30 years ago to evaluate the resistance of concrete piles. Currently only dynamic testing is used, both for mea- suring resistance and setup and for quality control (moni- toring stresses to reduce cracking and damage to concrete). Dynamic tests are sometimes done on pre-production test piles to set order lengths, while on some projects tests are on production piles only. Dynamic tests always include sig- nal match analysis using CAPWAP® software. Interestingly, NYSDOT reported that in practice they will use the super- position method (Hussein et al. 2002) noted in chapter two, adding base resistance from the end-of-initial drive (EOID) with the side resistance from restrike blows to estimate the static pile resistance. For very long piles, the side resistance from several blows is superimposed to estimate the side shear resistance for the pile. Driving Aids Driving aids have been used by only five of the 16 agencies and they highlighted the following useful practices: • Where concrete LDOEPs are used in sandy soils, such as by ALDOT and NYSDOT, jetting is allowed under cer- tain circumstances. Jetting involves using water delivered under pressure in a pipe with special nozzles to the pile tip to loosen the soil to make driving easier. Environmental issues related to turbidity usually require special mea- sures or can prohibit jetting at specific project sites. • FDOT allows jetting if environmental permits can be obtained, but tends to use pre-drilling or pre-forming holes no deeper than minimum tip elevations. Pre-drilling is allowed in the FDOT specification, but is not currently practiced with LDOEPs. • IDOT allows piles to be set and started with vibratory ham- mers, with completion or verification by impact hammer. • Caltrans has several allowable driving aids available to contractors, including driving shoes, pre-drilling, center relief drilling (drilling out the plug in the center of the pile), and vibration. Observations, Challenges, and Lessons Learned In the survey and during the interviews, respondents were given the opportunity to offer specific observations, lessons learned, or challenges from their experiences. Some of those not high- lighted in the previous sections of this chapter are noted here. ADOTPF • Do not use static analysis methods alone to predict resis- tance. They are too conservative as a result of not scal- ing up to larger diameters. • Have observed piles reaching a maximum resistance and then not gain additional resistance with increased depth. One idea is that the soil is liquefying close to the pile as it is being driven, causing reduction or loss of side resistance. Some gain occurs after driving has been completed, but not to the level expected. • Cleaning out the center of piles (center relief drilling) is effective for overcoming hard driving or obstructions in gravely soils. • If pile resistance is lower than the anticipated pile resis- tance from ADOTPF static analysis methods, increas- ing the frequency of high-strain testing to increase the resistance factor has been effective. Increased resistance factor decreases the required driving resistance. Caltrans • How to demonstrate and/or verify nominal axial resis tance: – PDA® alone for large diameter piles does not appear to adequately measure axial resistance.

32 – Pile driving formulas for large diameter piles are not sufficient. – Static pile load testing in conjunction with PDA® is needed according to the Caltrans LRFD Amendment to the AASHTO design code (California Department of Transportation 2012). – Load tests are needed to be taken to failure to better calibrate resistance factors; however, this is difficult. • Potential for effects of vibrations from installations in highly urbanized areas. More monitoring data and research is needed for LDOEP installations since most information is for small diameter piles. FDOT • Proper quantity, size, and location of vent holes in the sides of concrete cylinder piles are very important to reduce potential for longitudinal cracking as a result of stresses in the void space of the pile. • When driving concrete cylinder piles, the pile cushion needs to have a void with the same size as the void of the pile. Using a solid pile cushion may result in it being pushed into the void, generating radial stresses that ini- tiate longitudinal cracking or spalling at the pile head. • Careful consideration of the configuration of a driving helmet is important to avoid cracking resulting from mis- alignment and/or radial stresses at the top of the pile. • Evaluations of installed concrete cylinder piles that expe- rienced significant longitudinal cracking showed these piles performing very well for resisting corrosion (Lau 2005). LADOTD • Attention to the details of vent hole placement (for stress relief) and reinforcing at the top of concrete piles (for driving stresses). • Based on work for the LA 1 project, unit side resistance appears to be less for the larger diameter piles compared with small diameter piles. VDOT • The length and weight of LDOEPs requires good con- struction control to meet installation tolerances. • Installing LDOEPs as batter piles adds to the difficulty of meeting installation tolerances. • Good templates by the contractor help reduce the prob- lems of maintaining control of the pile during installation. RESEARCH NEEDS IDENTIFIED BY AGENCIES Through the survey and the interviews agencies using LDOEPs were asked what they perceived as areas needing research to better utilize these types of piles. These general areas included calculating axial resistance and the issues of appropriate resistance factors and installation methods. Specific suggestions included: • Developing new methods or improving existing meth- ods for calculating static resistance by accounting for the large pile sizes. • Developing appropriate resistance factors. • Better understanding of the mechanism of pile plug- ging, both during driving and under static loading. This also includes research on the effectiveness of forcing a pile to plug. • Investigating the impact on pile axial resistance if a vibratory hammer is used. • Correlations of soil resistance during driving to nominal axial static resistance. • Wave equation modeling of LDOEPs with insert plates or other devices to force the formation of a plug. • Effects on the formation of the plug when vibratory ham- mers are used. • Evaluating the time for setup of LDOEPs compared with closed-end piles or other pile types. • Determining the most appropriate or applicable failure criteria or mechanism. • Calibrating resistance factors and static analysis methods to dynamic testing. • Guidance on how to adequately perform signal matching and wave equation analysis for LDOEPS as compared with smaller piles. • Better understanding of the effects that the hammer impact on the pile has on pile resistance, particularly in cases of soils where piles do not increase resis- tance with depth resulting from soil remolding or other phenomena. • Increasing understanding and reliability of field verifi- cation of pile resistance.