Theoretical Analysis of Axial Compressive Load Transfer Mechanism of Anti-Toppling Helical Piles Embedded in Strain-Hardening Soils

Anti-toppling helical piles exhibit superior load-bearing performance due to enhanced interaction between the helices and the underlying soil; however, rigorous theoretical frameworks for their compressive analysis remain scarce. To address this limitation, this study proposes a computationally efficient analytical model utilizing the Modified Cam-Clay (MCC) constitutive framework to calibrate plane strain elements for pile–soil interaction simulations. Wedge-shaped and bulb-shaped fictitious soil pile models are introduced to accurately capture vertical capacity mobilization beneath the helix and pile tip, respectively. After successfully validating the framework against 3D finite element simulations and field test data, extensive parametric analyses were conducted. The key findings reveal that (1) unlike conventional piles, skin friction for anti-toppling helical piles increases monotonically with depth; (2) an optimal helix-to-pile diameter ratio of approximately 1.5 maximizes coordinated bearing capacity; (3) increasing pile length below a fixed helix depth provides negligible additional capacity; and (4) the critical state parameter M strictly controls the ultimate bearing threshold.