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5 is a summary of the principal findings of this study and pre- Structures Office (Bridge). Information provided includes a sents steps that can lead to more effective use, design, and brief description of the anticipated site conditions, conceptual construction of rock sockets for bridge foundations. In each foundation types considered to be feasible, and conceptual chapter, significant findings derived from the survey are iden- evaluation of potential geotechnical hazards such as lique- tified and discussed. Appendix A provides a list of survey re- faction. The purpose of these recommendations is to provide spondents and Appendix B presents the questionnaire and a sufficient geotechnical information to allow a bridge prelim- compilation of the responses to each question. inary plan to be produced. DESIGN PROCESS Develop Site Data and Preliminary Plan Structural foundation design within state DOTs is typically a Bridge obtains site data from the regional office and devel- joint effort between the structural and geotechnical divisions. ops a preliminary bridge plan (or other structure) adequate The geotechnical group may include engineering geologists for GD to locate borings in preparation for final design of the and both groups may operate under the supervision of a chief structure. Bridge would also provide the following informa- bridge engineer. As a starting point, consider Figure 2, which tion to GD to support development of the preliminary foun- shows a flow chart of the overall foundation design process. dation design: The chart is from the Washington State DOT Geotechnical Design Manual (2005). Based on responses to Question 4 of Anticipated structure type and magnitudes of tolerable the survey questionnaire (Appendix B) and interviews with settlement (total and differential). DOT personnel, Figure 2 typifies the process followed by At abutments, the approximate maximum elevation fea- many states. A summary of each step, also based on the sible for the top of the foundation. Washington State DOT manual (2005), is as follows. For interior piers, the number of columns anticipated and, if there will be single foundation elements for each Conceptual Bridge Foundation Design column or if one foundation element will support mul- tiple columns. An informal communication/report is produced by the Geo- At stream crossings, the depth of scour anticipated, if technical Division (GD) at the request of the Bridge and known. Typically, GD will pursue this issue with the Hydraulics Office. Known constraints that would affect the foundations in Bridge and Structures Office (Bridge) requests conceptual terms of type, location, or size, or any known con- foundation recommendations from Geotechnical Division straints that would affect the assumptions made to de- (GD) termine the nominal resistance of the foundation (e.g., utilities that must remain, construction staging needs, excavation, shoring and falsework needs, and other GD provides conceptual foundation recommendations constructability issues). to Bridge Preliminary Foundation Design Bridge obtains site data, GD provides preliminary develops draft preliminary foundation design plan, and provides initial recommendations A memorandum is produced by GD at the request of Bridge foundation needs input to GD that provides geotechnical data adequate to conduct struc- iterate tural analysis and modeling for all load groups to be consid- Bridge performs structural GD performs final ered. The geotechnical data are preliminary and not in final analysis and modeling and geotechnical design and form for publication and transmittal to potential bidders. At provides feedback to GD provides final geotechnical regarding foundation loads, report for the structure this stage, foundation recommendations are subject to type, size, depth, and change, depending on the results of structural analysis and configuration needed for structural purposes modeling and the effect that modeling and analysis has on foundation types, locations, sizes, and depths, as well as any design assumptions made by the geotechnical designer. Pre- liminary foundation recommendations may also be subject Bridge performs final structural to change based on construction staging needs and other modeling and develops final PS&E for structure constructability issues discovered during this phase. Geotech- nical work conducted during this stage typically includes com- FIGURE 2 Design process for Load and Resistance Factor pletion of the field exploration program to the final PS&E Design (Washington State DOT 2005). PS&E = Plans, level (Plans, Specifications, & Estimates), development of Specifications, & Estimates. foundation types and feasible capacities, foundation depths

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6 needed, p-y curve data and soil spring data for seismic mod- Anticipated foundation loads (including load factors eling, seismic site characterization and estimated ground and load groups used), acceleration, and recommendations to address known con- Foundation size/diameter and depth required to meet structability issues. A description of subsurface conditions structural needs, and a preliminary subsurface profile would also be provided Foundation details that could affect the geotechnical at this stage; however, detailed boring logs and laboratory design of the foundations, and test data would usually not be provided. Size and configuration of deep foundation groups. Structural Analysis and Modeling Final Foundation Design Bridge uses the preliminary foundation design recommenda- This design step results in a formal report produced by GD tions provided by GD to perform structural modeling of the that provides final geotechnical recommendations for the foundation system and superstructure. Through this model- subject structure. This report includes all geotechnical data ing, Bridge determines and distributes the loads within the obtained at the site, including final boring logs, subsurface structure for all appropriate load cases, factors the loads as profiles, laboratory test data, all final foundation recommen- appropriate, and sizes the foundations using foundation nom- dations, and final constructability recommendations for the inal resistances and resistance factors provided by GD. Con- structure. At this time, GD checks the preliminary foundation structability and construction staging needs continue to be design in consideration of the structural foundation design investigated during this phase. Bridge provides the following results determined by Bridge, and makes modifications as feedback to GD to allow them to check their preliminary needed to accommodate the structural design needs provided foundation design and produce the Final Geotechnical Re- by Bridge. Some state DOTs may also make this report avail- port for the structure: able to potential bidders. FIGURE 3 Design and construction process for drilled shaft foundations (adapted from Paikowsky et al. 2004a). QA/QC = quality assurance/quality control; NDT/NDE = nondestructive testing/evaluations.

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7 Final Structural Modeling and Development Design Process in Relation to the Synthesis of Plans, Specifications, and Estimates Based on the process described previously and followed by Bridge makes the required adjustments to the structural model most state DOTs, Figure 3 is a flowchart of the design and to accommodate changes in the geotechnical foundation construction process for drilled shaft foundations that pro- recommendations as transmitted in the final geotechnical vides a framework for the topics addressed by this synthesis. report. From this, the bridge design and final PS&E are In each subsequent chapter, the topics being covered are con- completed. A similar design process is recommended if a con- sidered within the context of the overall process as shown in sultant or designbuilder is performing one or both design Figure 3. This includes site investigation, geomaterial prop- functions. erty evaluation, and design for axial and lateral loading.