Impact of Groundwater Table Fluctuations on Uplift and Bearing Capacities of Short Straight-Shaft and Spiral Piles under Two-Way Cyclic Loading
Impact of Groundwater Table Fluctuations on Uplift and Bearing Capacities of Short Straight-Shaft and Spiral Piles under Two-Way Cyclic Loading
The growing demand for renewable energy has accelerated solar power installations, often on soft or sloped ground where short spiral (helical) piles are preferred for their strong uplift resistance and ability to reinforce slopes through rotational penetration. These piles are also widely used in subway platform door foundations. However, fluctuations in the groundwater table (GWT) can significantly influence their axial performance. This study experimentally examines the effects of GWT variations on the uplift and vertical bearing capacities of short straight-shaft and spiral piles subjected to two-way cyclic loading. Initial tests in fully saturated silica sand established baseline behavior. Lowering the GWT increased both uplift and bearing capacities due to soil desaturation, enhanced matric suction, and greater effective stress, improving soil-pile interaction. The spiral pile, which mobilizes additional shaft friction along its helical blades, exhibited a more pronounced capacity increase than the straight-shaft pile. Under unsaturated cyclic loading, both piles experienced performance degradation caused by suction-maintained gaps forming around the pile, reducing tip and shaft resistances. Upon re-saturation, suction dissipated and sand flowed into these gaps, restoring soil-pile contact and resulting in bearing capacity recovery. Although the recovered capacity remained lower than under unsaturated conditions, it exceeded the initial saturated state due to localized densification and enhanced interparticle interlocking from prior cyclic loading. These findings highlight the critical role of suction and re-saturation processes in governing pile behavior under cyclic loading and emphasize the need to incorporate groundwater fluctuation effects in the design of short piles for solar panels.
Faheem Shah; Koichi Isobe
11th International Conference on Physical Modelling in Geotechnics (ICPMG2026)
Session 3: Resilient geotechnical infrastructure
https://doi.org/10.53243/ICPMG2026-196