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4 P shaft design were consulted. These include Drilled Shafts: M Construction Procedures and Design Methods by O'Neill H and Reese (1999) and the AASHTO LRFD Bridge Design Specifications (3rd ed. 2004). In addition, a draft version of Section 10, "Foundations," of the 2006 Interim AASHTO LRFD Bridge Design Specifications was reviewed. A questionnaire was developed and sent to the principal SOIL geotechnical and structural engineers of 52 U.S. transportation agencies (including Puerto Rico and the District of Columbia) and the Canadian provinces. The primary purpose of the survey was to define the current state of practice for rock-socketed shafts. Questions were grouped into the following categories: WEATHERED ROCK OR IGM Use of rock-socketed shafts by the agency, Evaluation of rock and IGM properties, ROCK Design methods for axial loading, Design methods for lateral loading, Structural design, FIGURE 1 Rock-socketed shaft designed for highway bridge Construction, and structure. Field load and integrity testing. The major challenges faced by U.S. transportation agencies Thirty-two U.S. and one Canadian provincial transporta- in the use of rock-socketed drilled shafts for highway bridges tion agencies responded to the questionnaire, completely or were identified by NCHRP Topic Panel 36-12 as follows: in part. A list of responding agencies and a summary of re- sponses to the questions are given in Appendix A. The ques- The first challenge is characterizing the nature of the tionnaire was also sent to several consulting firms and drilled rock or IGM. By its nature, rock and IGM are highly shaft contractors. Two contractors responded to the survey. variable and difficult to characterize for engineering Based on responses to the questionnaire, selected state purposes. To effectively design drilled shafts in rock and agency personnel and contractors were interviewed. IGM, engineers must accommodate high levels of un- certainty. Issues to be addressed include quantifying material characteristics, rock mass behavior, and appro- priate application of laboratory and field test methods. ORGANIZATION OF SYNTHESIS The second challenge is determination of the axial load The synthesis is presented in six chapters and two appendixes. capacity of rock-socketed shafts. Rock-socketed shafts Chapter one defines the problem, objectives, scope, and resist axial load in both side shear and end bearing. De- methodology of the study. This chapter also provides an signers need well-documented methods for assessing overview of the foundation design process used by state de- side shear and end bearing. Different methods are ap- partment of transportation (DOT) agencies. This overview propriate for different types of geology. There are many provides a framework for understanding the interrelationships issues related to characterizing the rock and construc- between site characterization, material property evaluation, tion that affect design for axial loading. geotechnical and structural design, load testing, and con- The third challenge is analysis and design of rock- struction of rock-socketed shafts. Each of these topics is con- socketed shafts under lateral loading. It has been a cus- sidered in subsequent chapters. Chapter two reviews methods tomary practice to adopt the techniques developed for of site characterization and material property evaluation that laterally loaded piles in soil to solve the problem of are applicable to rock-socketed shafts. Chapter three is a com- rock-socketed shafts under lateral loading. There exist pilation and critical review of methods used for analysis and several analysis and design methods specifically for design of rock sockets for axial loading. Chapter four reviews rock-socketed shafts under lateral loading; their appli- and summarizes analysis methods for rock sockets under lat- cation in practice remains limited. eral and moment loading and discusses structural design is- sues relevant to rock sockets. Chapter five provides an METHODOLOGY overview of current technologies for rock-socket construction and considers some of the construction issues identified by A literature review was conducted on all topics related to the survey. This chapter also covers field load testing of rock- drilled shafts in rock or IGM. To assess current practice, the socketed shafts and the role of load testing within the context primary manuals used by transportation engineers for drilled of state DOT foundation engineering programs. Chapter six