Uplift Capacity of Small‐Diameter Drilled Shafts from In Situ Tests

Abstract

Predictions of the ultimate uplift capacity of six small‐diameter drilled shafts installed in stiff cohesive soil are compared with pullout tests conducted to failure. The shafts were installed by the dry‐hole method with gravity free‐fall concrete placement, and were 76 mm and 152 mm in diameter with lengths ranging from 1.52 to 4.57 m. Predictions of the ultimate uplift capacity were made assuming that failure takes place as a result of perimeter shear. An effective stress model was used with soil parameters obtained from in situ tests. Soil shear strength was obtained from the results of borehole shear tests, and an interpreted profile of in situ, at‐rest horizontal soil stress was obtained from the results of prebored pressuremeter tests. The results of the test program demonstrate that the borehole shear test and pressuremeter test may be used in combination to design drilled shafts for uplift resistance in stiff soils.