A Method for Calculating Uphill Direction Lateral Response of Flexible Monopiles near the Slope Toe in Sand

Deck arch bridges are a suitable structural solution for spanning V-shaped valleys. Pile foundations at arch seats of these bridges are typically subjected to lateral loads in the uphill direction, demonstrating distinct load-bearing characteristics compared with piles on flat ground. This study proposes a failure-wedge model that incorporates slope angles and the distance of the pile from the slope toe, considering both pile–soil interface friction and wedge base-angle variations. An analytical formulation was developed to quantify ultimate soil resistance for piles under lateral loads in the uphill direction in a cohesionless slope, and the calculation depth of the deep-plane failure mechanism was modified. The method’s feasibility was validated through comparison between theoretical predictions and numerical simulation results. Results show that increasing slope angle significantly enhances shallow-soil resistance around piles. The neglect of shallow pile–soil interface friction leads to underestimation of lateral bearing capacity. When the slope angle increases to 30°, variations in wedge base angle significantly affect shallow-soil ultimate resistance. The use of fixed base angles in calculations produces unreasonably shallow-soil ultimate resistance values.