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.

This study investigates the application of machine learning (ML) algorithms for seismic damage classification of bridges supported by helical pile foundations in cohesive soils. While ML techniques have shown strong potential in seismic risk modeling, most prior research has focused on regression tasks or damage classification of overall bridge systems. The unique seismic behavior of foundation elements, particularly helical piles, remains unexplored. In this study, numerical data derived from finite element simulations are used to classify damage states for three key metrics: piers' drift, piles' ductility factor, and piles' settlement ratio. Several ML algorithms, including CatBoost, LightGBM, Random Forest, and traditional classifiers, are evaluated under original, oversampled, and undersampled datasets. Results show that CatBoost and LightGBM outperform other methods in accuracy and robustness, particularly under imbalanced data conditions. Oversampling improves classification for specific targets but introduces overfitting risks in others, while undersampling generally degrades model performance. This work addresses a significant gap in bridge risk assessment by combining advanced ML methods with a specialized foundation type, contributing to improved post-earthquake damage evaluation and infrastructure resilience.

Helical piles can be rescrewed at greater depths after failure and put back into service again as long as their integrity is preserved. However, reports on the lifetime performance after reinstallation are completely missing in the literature. This work compares the tensile cyclic response of single helix piles in dry and saturated sand after experiencing failure due to monotonic uplift and after reinstallation, using centrifuge model testing. Tensile cyclic tests were conducted on three model piles with different helix-to-shaft diameter ratios, under two different conditions: (1) cyclic loading after monotonic pile failure, and (2) cyclic loading on a pile that has been reinstalled deeper into the soil after experiencing a monotonic failure. The experiments revealed that the preceding monotonic failure causes significant influence on the post-failure cyclic performance, in which few tens of cycles are enough to lead to a critical accumulated displacement. The cyclic tests on the reinstalled helical pile at a depth of 2D (D = helix diameter) below the initial helix depth showed that the cyclic performance can be partially to fully recovered depending on the loading amplitude.

For an offshore photovoltaic helical pile foundation, significant horizontal cyclic loading is imposed by wind and waves. To study a fixed offshore PV helical pile's horizontal cyclic bearing performance, a numerical model of the helical pile under horizontal cyclic loading was established using an elastic-plastic boundary interface constitutive model of the clay soil. This model was compared with a monopile of the same diameter under similar conditions. The study examined the effects of horizontal cyclic loading amplitude, period, and vertical loads on the horizontal cyclic bearing performance. The results show that under horizontal monotonic loading, the bearing capacities of a helical pile and monopile in a serviceability limit state are quite similar. However, as the amplitude of horizontal cyclic loading increases, soil stiffness deteriorates significantly, leading to greater horizontal displacement accumulation for both types of piles. The helical pile's bearing capacity under horizontal cyclic loadings is approximately 60% of that under monotonic loading. With shorter cyclic loading periods, horizontal displacement accumulates rapidly in the initial stage and stabilizes over a shorter duration. In contrast, longer cyclic loading periods lead to slower initial displacement accumulation, but the total accumulated displacement at stabilization is greater. When vertical loads are applied, the helical pile exhibits more stable horizontal cyclic bearing performance than the monopile.

Helical piles can be classified as partial displacement piles in terms of moderate advancement rate. However, its installation effect on surrounding soil is unclear. This study presented four field tests on the installation of helical piles with various dimensions in silty clay. The radial earth pressure and excess pore water pressure were measured during the installation processes. The installation effect of helical pile embedded in silty clay was comprehensively discussed and evaluated from multiple dimensions of time and space, based on the cavity expansion method (CEM) and Randolph and Wroth's elastic-plastic method verified by field data. The research reveals that as the length of the helical pile increases by 1.0 time, the maximum variations in radial earth pressure and pore water pressure by a remarkable 25.0 times and 7.8 times, respectively. Additionally, when the shaft diameter of the helical pile expands by 20%, the maximum alterations in radial earth pressure and pore water pressure swell by approximately 18.6 and 5.7%, respectively. Comparing the radial earth pressure at various embedment depths at the same penetration stage, it is found that the radial earth pressure induced by helices is slightly greater than that induced by pile shaft. The estimated radial earth pressure and pore water pressure agree with the measured maximum data, and the pore water pressure generated by the installation of helical pile completely dissipates after 10-12 days of installation in this work.