Multiangle helical piles are used to support multidirectional loads. The load transfer behavior of inclined piles may differ from that of vertical piles. Vertical compressive and oblique uplift load field tests were conducted on a multiangle helical pile group and two single helical piles embedded in silty clay. The load-bearing capacities, group effects, load transfer behavior, earth pressure, and excess pore water pressure were investigated. The results show that the vertical compressive and oblique uplift capacities of the 10 degrees-inclined single helical pile were improved by 12% and 95% compared to those of the vertical single helical pile, respectively. The inclined installation of helical piles significantly optimized the load transfer mechanism of the piles under oblique loads. The group efficiency of the multiangle helical pile group was approximately 102%, attributed to the increased pile spacing resulting from the inclined installation. During loading, the helices and pile toe together contribute more than 50% of the bearing capacities of helical piles. The earth pressure and excess pore water pressure around the grouped helical pile, particularly near the bottom helix, exhibited less variation than those around the single pile, suggesting a smaller disturbance in the surrounding soil.

Previous earthquake events indicate that pile foundations in liquefiable soils are vulnerable to damage due to the coupling of inertial and kinematic effects. Inclined piles are widely applied in structures located in liquefiable soils, but few investigations of the coupling of the superstructure-pile inertial and soil-pile kinematic effects have been conducted. To address this gap, this study adopted a three-dimensional (3D) numerical model to investigate the coupling of inertial and kinematic effects in pile foundations with different inclination angles. The pile head bending moment was employed to represent the pile response, while the soil surface displacement and structure acceleration were utilized to quantify the kinematic and inertial effects. The role of the inclination angle on the interactions between inertial and kinematic effects is herein considered for pile groups. In particular, the inertial effect significantly influences the behavior of pile groups with larger inclination angles, whereas the kinematic effect predominates the pile head moment in vertical pile groups. In this paper, the influence of the pile inclination angle, superstructure configuration, and earthquake intensity on the interactions was investigated. The principal findings revealed that the kinematic effect dominates in the vertical pile group irrespective of the properties of the superstructure, while the inertial effect plays a significant role in the response of the inclined pile groups, especially for superstructures with considerable heights. Inclined piles are vulnerable to damage due to the interaction of inertial and kinematic effects during earthquakes. This study conducted a series of three-dimensional (3D) finite-element simulations to investigate the interaction of inertial and kinematic effects in pile foundations with different inclination angles. The influence of pile inclination angle, superstructure height, and earthquake characteristics was investigated. In current practices, various codes and pseudostatic methods have been adopted to sum a percentage of the inertia-induced bending moment and another percentage of the kinematic-induced bending moment. This study indicates that under certain conditions, the simple summing of the bending moment induced by the inertial and kinematic effects could be inaccurate. The present study identified several factors that influence the interaction of inertial and kinematic effects on piles with different inclination angles. The inclined piles in liquefied soil, especially for supporting tall and heavy superstructure, attention should be given to the influence of inertial effect on the pile head bending moment.