OPTIMIZATION OF GROUTING METHOD AND AXIAL PERFORMANCE OF PRESSURE GROUTED HELICAL PILES

Pressure grouted helical pile (PGHP) is an innovative piling system that allows a significant increase in helical pile capacity with relatively low additional cost. The pile is constructed by applying pressurized grout during the installation of conventional helical piles. The grout is injected into the ground through two nozzles welded to the hollow pile shaft. This paper presents a comprehensive laboratory study to investigate the effect of three different nozzles configurations on the shape and axial performance of PGHP. The results reveal a significant increase in the PGHP shaft resistance over that of the un-grouted helical pile due to the formation of a continuous grout column with a larger diameter, higher friction angle at the pile/soil interface, and higher lateral earth pressure around the pile. The shape and diameter of the created grout column depend on the nozzles configuration used for grout injection. An increase in the end-bearing resistance is observed due to grout dissipation into the supporting soil voids. The study also shows that PGHPs installed with the third nozzles configuration have the fastest installation rate and the highest compression and pullout resistances. Thus, the third nozzles configuration is recommended for PGHP construction.

FIELD STUDY OF GROUP EFFECTS ON THE PULLOUT CAPACITY OF ‘DEEP’ HELICAL PILES IN SAND

This paper presents the results of a field load test program used to investigate group effects on the pullout capacity of single-helix ‘deep’ helical piles/anchors in sand. The high tensile capacity and silent installation of helical piles has given them serious consideration as an alternative to conventional deep foundations and anchors for offshore renewable energy structures. New offshore applications may consider the use of groups of helical piles to resist structural loads. Group interaction effects are known to occur in helical piles but there is a scarcity of field data on groups in sands under tensile loading. This study involved the installation and load testing of single-helix 152-mm diameter round shaft piles and pile groups embedded in sand to depths of 12 and 18 helix diameters below the ground surface. The study was designed to explore the effects of close pile spacing, group configuration (i.e. number of piles), and soil strength as interpreted from Cone Penetration Test (CPT) resistance. The results showed group efficiencies ranging from about 0.6 to 1.0 at a horizontal spacing of 2 to 3 times the helix diameter in sands with friction angles of about 39 to 44 degrees. The data from this study may also be useful for calibration and validation of numerical models for further analysis of helical pile group interactions.

Model Uncertainties in Foundation Design

The book focuses on providing a foundation designer information on the model factor and its statistics for conventional foundation types such as shallow foundations, driven piles, and drilled shafts as well as special foundations such as spudcans and helical piles. Besides foundations, the book also provides information for other geostructures such as mechanically stabilized earth (MSE) walls, soil nail walls, pipes and anchors, slopes, and braced excavations.