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1 CHAPTER 1 Introduction This Final Report summarizes work that was carried out on · Optimizing design approaches for both routine design and National Cooperative Highway Research Program (NCHRP) special design cases using more comprehensive methods; Project 12-70 Seismic Analysis and Design of Retaining Walls, · Avoiding hidden conservatism in design approaches; Buried Structures, Slopes, and Embankments. This project in- · Ensuring applicability of specifications to seismic zones volved an effort to develop analysis and design methods and nationwide, including provisions for "no seismic design" recommended load and resistance factor design (LRFD) spec- in low seismicity regions; and ifications for the seismic design of retaining walls, slopes and · Satisfying LRFD philosophy and providing flexibility in embankments, and buried structures. establishing serviceability criteria. 1.1 Overall Project Objectives, The approach for the Project initially focused on data col- Approach, and Schedule lection and review during Task 1, leading to the documentation The overall objectives of the Project were to develop analysis of problems and knowledge gaps in Task 2. The problems and and design methods and to prepare LRFD specifications and ex- knowledge gaps identified in Task 2 were used to recommend ample problems for the design of retaining walls, slopes and em- analytical methodology developments in Task 3, and a detailed bankments, and buried structures. These overall objectives were work plan in Task 4. The results of these four tasks were intended to address short-comings in AASHTO LRFD Bridge summarized in Task 5, the first Interim Report. This phase of Design Specifications or in some cases the absence of a recom- the work occurred within the first 9 months of the planned mended design methodology in the LRFD Specifications. 39-month project duration. The approach used to address these two objectives was out- Following submittal of the first Interim Report and the lined in a Working Plan submitted by the Project Team to NCHRP Oversight Panel's review and approval of the work NCHRP in May of 2004. The Working Plan is based on CH2M plan described in the first Interim Report, the approved work HILL's proposal to NCHRP in November of 2003, with mod- plan was implemented in Task 6. An outline of the LRFD ifications summarized in Attachment 2 of CH2M HILL's letter specifications was prepared in Task 7, and the results of the dated January 13, 2004, to Dr. Robert Reilly of the Transporta- analytical developments and LRFD specification outline were tion Research Board. Also included in this Working Plan was summarized in Task 8, which was identified as the second In- a Progress Schedule tied to the Project start date of March 29, terim Report. The submittal of the second Interim Report 2004, and a Table of Deliverables for this Project. A copy of concluded Phase 1 of the Project. The schedule for complet- the Working Plan for the Project is included in Appendix A ing the second Interim Report was originally planned to be to Volume 1 of this Final Report. approximately 22 months after the initiation of the Project; Five fundamental goals were identified during the plan- however, actual work took approximately 24 months. ning of the Project in 2004. These goals formed the basis for Phase 2 was initiated upon completion of Task 8. This the work that was to be done during each Project activity. The phase involved Task Orders 9-12, where specifications, com- five goals involved mentaries, and example problems were prepared and sub- mitted to the NCHRP Oversight Panel for review. The third · Improving existing or developing new analytical methods Interim Report provided the first draft of the specifications, to overcome the shortcomings of existing technology, commentaries, and example problems, in accordance with based on sound soil-structure interaction principles; the requirements of Task 10. Following receipt of comments