Terrain slope angle effect on p–y curves for piles in gravelly soil

Abstract

Horizontal resistance can be significantly different for gravel soil slope sites with different gradients. Slope angle effects on the horizontal resistance and the safety and stability of the structure are important in the design of pile foundations. In this paper, the effects of slope angle on the p–y curves are studied via in situ lateral load testing on eight piles installed in gravelly soil; the deflection of piles versus load curves and the resulting p–y curves for piles at different slope angles are compared. The outcomes are used to establish the initial stiffness (k_ini) and the ultimate subgrade reaction of soil (p_u) as a function of the slope angle, which can be used to further develop standardized p–y curves for gravelly soil conditions in sloping ground. The analysis shows the proximity of the slope angle has small effects on k_ini of the p–y curves when soil displacement is under 3 mm; otherwise, the proximity of the slope angle adversely affected the p–y curves. Furthermore, k_ini is reduced close to the ground surface and gradually increases with depth until it finally becomes equal to the value of level ground. The ratio between p_u in slope ground and level ground was determined as 0.79, 0.63, and 0.50 for slope angles of 15°, 30°, and 45°. The newly developed p–y curves were cross-validated using another in situ test. The findings of these analyses showed that the predicted responses of piles with the new p–y curves are in good agreement with the results of the in situ test. The difference between the actual and predicted p–y curves was approximately 20% for maximum bending moment and 5–10% for maximum displacement.