Predicting End Bearing Capacity of Post-Grouted Drilled Shaft in Cohesionless Soils

Although pressure grouting beneath the tips of drilled shafts had been used successfully worldwide for close to 4 decades, it has remained relatively unused in the United States in part due to the absence of a rational design procedure. Previous international usage relied predominantly upon experience and unpublished proprietary approaches. More recently, research aimed at quantifying the improvement that could be derived from postgrouting drilled shaft tips has resulted in a design methodology. This paper briefly discusses the postgrouting process and outlines the full scale test programs used to identify parameters affecting postgrouting performance. Correlations developed between applied grout pressure and end bearing improvement are presented along with a numerical example illustrating the design procedure.