Study of grouted deep foundations in cohesionless soils

Grouting of deep foundation subsequent to installation has become popular due to its effectiveness in improving axial capacity under serviceable displacement. Post tip grouting of drilled shafts has been successfully employed worldwide to mobilize a significant portion of tip resistance under small displacements. Recently, Florida Department of Transportation developed a new jetted and grouted precast pile system and the construction of the pile utilizes the advantages of several proven deep foundation installation techniques.;This research focused on the individual and group behavior of jetted and grouted piles and tip grouted drilled shafts in cohesionless soils. Experimental study and numerical modeling of both types of foundations were performed to investigate the response in individual and group scenario. Based on the study, a methodology for jetted and grouted piles that predicts expected grout pressures during grouting, unit side and tip resistance and the load-displacement response of the pile is proposed. In case of post grouted drilled shafts, the study found that the increased axial capacity under serviceable displacements depended mainly on preloading effects and the increased tip area provided by the grouting process. A simple prediction approach for estimating the tip capacity of grouted shafts utilizing cone penetration resistance was suggested based on the results of the study. The validity of the proposed approach was verified by the analysis of full-scale case studies of grouted shafts reported in the literature.;The experimental group study at 3 x pile/shaft diameter (D) center-to-center spacing revealed that the jetted and grouted piles behaved as a block during axial loading, whereas the post grouted drilled shafts acted independently of one another, i.e., negligible group interaction. It was also identified that the side grouting of a foundation prior to tip grouting has a substantial influence on improving the axial capacity. The side grouting was found to significantly increase the grout pressure developed during tip grouting and helps in the formation of tip grout bulb by spherical cavity expansion process and thus improves the unit tip resistance of the foundation.