Centrifuge investigation of pile base effect on the lateral load capacity for large diameter rigid piles embedded in sand

Large-diameter drilled shafts show rotational-behavior under lateral loads inducing pressure on pile base, which may affect the lateral load capacity. This study examines the effect of pile base pressure (p base ) to the lateral load capacity of large-diameter drilled shafts in sand. A series of centrifuge tests were conducted on model piles with varying slenderness ratios (L/D) and soil conditions, where p base was directly measured. The lateral load–displacement responses, bending moments (BM), and p base distributions were systematically analyzed. Test results revealed that p base was asymmetrically distributed across the pile base and played a non-negligible role in the overall lateral resistance. The values of BM mobilized at the pile base (BM b ) were evaluated to quantify the effect of p base . The contribution of BM b to total BM (BM t ) increased with decreasing L/D and increasing pile stiffness, particularly in loose sands. At the ultimate limit state (ULS), percent ratio of BM b /BM t ranged from 3.6% to 15.0%, while it reached up to 25.7% at the serviceability limit state (SLS). Based on these results, a modification factor to quantify the contribution of BM b to the lateral load capacity was proposed with the goal of establishing a more robust and optimized design strategy for drilled shafts.