O-Cell Test Results for Drilled Shafts in Marl and Limestone

The replacement of the existing I-95 Fuller Warren Bridge over the St. Johns River in I Jacksonville, Florida, required the installation of more than 750 drilled shafts founded in limestone and marl for support of the new 2,304-m (7,559-ft) long bridge. This project included Osterberg load cell tests on 915, 1220, and 1830-mm (36, 48 and 72-inch) diameter drilled shafts located on land and in the river to confirm shaft capacities and to establish shaft tip elevations for construction. One of the test shafts had a single O-Cell® while the remaining three test shafts had two levels of O-Cells to determine both ultimate friction and end bearing resistance. The two shafts in the river were installed with isolation casing to eliminate shaft friction above the design scour elevation. The paper describes the design of the drilled shaft foundations and the installation of the test shafts. The paper also presents and discusses the results of the O-Cell load tests, and compares the test results with predicted design values. In addition, the paper provides a comparison of the test results with values predicted using methods described by O'Neill and Reese in the current FHWA manual on drilled shaft construction and design. The data evaluation also includes an assessment of the influence of the hydrostatic pressure of the plastic concrete on friction resistance by comparing the results of two 1,830-mm (72-inch) diameter shafts.