Evaluation of Base Grouted Drilled Shafts at the Audubon Bridge

The load test program for the Audubon Bridge project provides a comparison of the performance of base grouted and ungrouted shafts on large diameter foundations in sand. Comparison of several field load tests at the two pylon foundations indicate that the base grouting operations more than doubled the available base resistance, and provided for consistent load-deflection behavior in sand with varying properties. Base grouting of all the production shafts also provided a verification of axial resistance. The Audubon Bridge will be a new Mississippi River crossing near St. Francisville, Louisiana, and the two main pylons of the cable-stayed span are each supported by a 3 x 7 group of 2.29m (7.5ft) diameter drilled shafts. The drilled shafts bear in an alluvial sand and gravel formation at an elevation about 61m (200ft) below the surface. Underlying this formation was a clay with less potential base resistance for deep foundations.