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8 that explains the methodology and provides design examples 1.4 RESEARCH APPROACH (Orr and Farrell, 1999; see also Orr, 2002). The final draft of the future Eurocode 7 (October 2001, see also Frank, 2002) 1.4.1 Design and Construction Process of Deep Foundations is an extensive code that is expected to become an EN pub- lication by August 2004. This detailed document contains Figure 3 presents a flow chart depicting the design and 12 sections dealing with all geotechnical design aspects rang- construction process of deep foundations. Commonly, design ing from geotechnical data (section 3), to construction super- starts with site investigation and soil parameter evaluation, vision (section 4), to hydraulic failure (section 10). Section 7 assessments that vary in quality and quantity according to the is dedicated to pile foundations. While not very detailed importance of the project and complexity of the subsurface. regarding a specific determination of the pile capacity, the Possible foundation schemes are identified based on the results code is elaborating for all cases (i.e., static load test results, of the investigation, load requirements, and local practice. All static and dynamic methods) factors to be applied to both the possible schemes are evaluated via static analyses. Schemes minimum and average of the capacity as a function of the for driven piles also require dynamic analysis (drivability) for number of applications. For example, static load test capac- hammer evaluation, feasibility of installation, and structural ity will have factors (to be divided by) ranging from 1.4 to adequacy of the pile. In sum, the design stage combines, 1.0 when applied to the results of 1 to 5 or over load tests. therefore, structural and geotechnical analyses to determine Specifically, if, for example, three static load tests are carried the best prebidding design. This process leads to estimated out, the mean value of the three will be divided by 1.2, and quantities to appear in construction bidding documents. the minimum value by 1.05, and the lower of the two will Upon construction initiation, static load testing and/or determine the factored resistance to be used. dynamic testing, or dynamic analysis based on driving resis- Substantially fewer details are provided by the codes for tance (using dynamic formulas or wave-equations) are LRFD design of drilled shafts. The two extremes being the carried out on selected elements (i.e., indicator piles) of the aforementioned Bridge Code (1992), in which drilled shafts original design. Pile capacity is evaluated based on the con- are included under a single category of cast-in-place piles struction phase testing results, which determine the assigned ( = 0.4 like all other concrete piles), and the AASHTO rel- capacity and final design specifications. In large or important atively detailed provisions described in section 1.3.5.2. projects, the pile testing may also be used as part of the design. Two requirements are evident from this process: (1) pile evaluation is carried out at both the design and the construction stage, and (2) these two evaluations should 1.3.5.4 Difficulties with the Existing LRFD Codes result in foundation elements of the same reliability but pos- sibly different number and length of elements depending on All existing codes suffer from two major difficulties. the information available at each stage. One is the application of LRFD to geotechnical problems as described in section 1.3.4 (e.g., site variability, con- struction effects, past experience, etc.). The other problem 1.4.2 Overview of the Research Approach is lack of data. None of the reviewed codes and associated resistance factors were consistently developed based on data- The complete application of LRFD to the process described bases enabling the calculation of resistance factors from case in Figure 3 requires an integrated framework. For example, histories. the method by which a field test (say SPT) is used to obtain The current AASHTO specifications of driven piles soil parameters must be coordinated with the method used for reviewed in section 1.3.5.1 encounter additional difficulty static capacity of the pile, and both must be coordinated with due to the multiplication of the resistance factor by the mod- the assessment of uncertainty. Independently, one needs to ifier v. This procedure requires the interaction of two inde- evaluate the design verification process during construction, pendent pile capacity evaluations (e.g., static analysis and i.e., static load testing and dynamic testing to assess and mod- dynamic methods) and results in unnecessary and confusing ify the pile installation, as well as quality assurance (e.g., conservatism. A clear separation of the resistance factors on nondestructive testing of drilled shafts) and related issues. the basis of design and construction is required and is one Previous LRFD developments, using back analysis of aim of the present study. As a result of the aforementioned ASD and judgment, have addressed some of these issues difficulties, the current AASHTO LRFD specifications for (e.g., Withiam et al., 1998). The present effort to assemble a geotechnical applications are of limited use. Two surveys case history database adds other difficulties, for example presented in this report (see section 2.1) found that only determining a "predicted" capacity that can be compared 14 states (30%) are currently committed to the use of LRFD with measured load-test values. in foundation design. In contrast 93% of the responding use The present effort was focused on calibrating the direct WSD, suggesting that most of those that use LRFD are uti- design and construction evaluation process. For the design, lizing the methodology in parallel to WSD. specific methods and correlations were chosen. Their results