Axial Behavior of Pressure Grouted Helical Piles Installed in Marine Soft Clay Based on Full-Scale Field Tests

Pressure grouted helical pile is an innovative soil–cement helical pile constructed by applying pressured grouting during the installation of the helical pile. Compression and tension field tests were presented to investigate the axial behavior of pressure grouted helical piles installed in clay deposits. Six compression and four tension tests were conducted, including three un-grouted helical piles, five pressure grouted helical piles, and two hollow-bar micropiles. From the observation of the excavated piles, a continuous soil–cement column could be created with a diameter larger than the helix plate. The load transfer analysis based on the strain gauge measurements showed that the pressure grouted helical piles increased the pile resistance in the clay layers. The maximum skin friction of the mud clay under compression was improved by 75%. The larger soil–cement column diameter and higher ultimate skin friction strengthened the pile stiffness and contributed to the increase of the overall axial capacities. In this study, the axial capacities of the pressure grouted helical piles were approximately two times that of the un-grouted helical piles. The overall results demonstrated that the pressure grouted helical pile was an enhanced construction method that can improve axial capacities in marine soft clay compared to the un-grouted helical piles.