Field Tests on the Installation Effect and Bearing Capacity of Inclined Helical Piles in Silty Clay

The installation effects and bearing performance of inclined helical piles have garnered significant attention due to their increasing application in supporting loads from transmission towers. This study presents three field tests on the installation of helical piles with inclinations of 0°, 5°, and 10° in silty clay. Two load tests were conducted on helical piles inclined at 0° and 10°. The installation effect, bearing capacity, and torque factor were investigated. A theoretical model was developed to estimate the installation torque, incorporating the pile’s inclination angle and the anisotropy of soil shear strength. The results show that pile inclination pronouncedly influenced installation torque and bearing performance. Specifically, the 10°-inclined helical pile outperformed the vertical pile in terms of torque factor and bearing capacity, with increases of 16.3% and 12.2%, respectively. During installation, pore-water pressure and soil stress showed reasonable agreement with predictions from the cavity expansion method and followed a logarithmical decrease with increasing radial distance. Near the pile wall, the maximum changes in pore-water pressure and soil stress were estimated to be 4.3suv and 5.3suv, respectively, where suv is the undrained shear strength in the vertical direction.