Use of In Situ Tests to Design Drilled Shafts in Dense and Cemented Soils

In the desert southwest of the United States (Arizona and parts of New Mexico, California, Nevada, Utah and Colorado), the soils are often dense and cemented. The design procedures for drilled shafts described by the American Association of State Highway and Transportation Officials (AASHTO) or the Federal Highway Administration (FHWA) do not incorporate the effect of density or cementation. Use of β-α methods cited in these publications often result in an over-design of the drilled shafts with associated greater costs. The FHWA publication by O'Neill and Reese suggests classifying dense or stiff soils as intermediate geomaterials (IGMs) and proposes alternative design methodology. Based on results of the recent large-scale load tests in Arizona reported in this paper (2.44 m diameter test shaft) and the results of tests in New Mexico described by Chua et al. (1.37 and 1.83 m diameter test shafts), it appears that the actual skin friction in desert southwest soils is much higher than that predicted by the equations for IGMs. This paper presents the results of the test program performed for the Arizona Department of Transportation (ADOT) that included a large scale load test on a 2.44 m diameter, 41.1 m deep shaft to re-design large diameter drilled shaft foundations for the I-10/I-19 Traffic Interchange (TI) in Tucson, Arizona. The methodology implemented on this successful project may be useful for future projects in dense and variably cemented soils.