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Drilled shafts are one of the few structural foundation types that can be built directly into rock. Foundations in rock are attractive because high load carrying capacities are possible and foundation displacements can be limited to acceptable levels more readily than through foundations in soil. Over the past 25 years, much knowledge and experience has been gained by the engineering and construction industries with the use of rock-socketed drilled shafts for support of transportation structures. The goal of this synthesis is to collect, review, and organize the most salient aspects of that knowledge and experience and to present it in a form that is useful to foundation designers, researchers, contractors, and transportation officials. Challenges faced by foundation designers when considering rock-socketed drilled shafts include: (1) characterizing the nature of the rock mass or intermediate geomaterial, (2) select- ing appropriate design methods for analysis of axial load carrying capacity and axial load- deformation response, (3) analysis and design for lateral loading, and (4) assessing issues of constructability and their influence on foundation performance and costs. Each of these issues is considered in the synthesis within the context of the overall foundation design process as practiced by transportation agencies. A survey questionnaire was developed and distributed to the principal geotechnical and structural engineers of 52 U.S. transportation agencies (including Puerto Rico and the Dis- trict of Columbia) and Canadian provinces. The purpose of the survey was to define the cur- rent state of practice for rock-socketed drilled shafts. Thirty-two U.S. transportation agencies and one Canadian provincial transportation agency responded to the questionnaire. Innovative methods for field load testing of drilled shafts, including the Osterberg Cell and Statnamic methods, have contributed to advances in design and construction of shafts in rock. Load testing is shown to be an integral part of several state department of transporta- tion programs that have led to increased use of rock-socketed drilled shafts and improved de- sign methods. These and other load testing methods for rock-socketed shafts are reviewed. ROCK-SOCKETED SHAFTS FOR HIGHWAY STRUCTURE FOUNDATIONS SUMMARY
