Comparative study on bearing properties of bored piles with two different length-to-diameter ratios by field tests in sand/silty clay formation

Based on full-scale field static load tests in sandy/silty clay, this study compares the bearing and deformation characteristics of pile-tip post-grouted bored piles with different length-to-diameter ratios (L/D = 33.3 and 48.0). Both types of piles behave as friction piles. The small L/D piles (short length, large diameter) exhibit better load-bearing performance and smaller settlement under the same load. Their axial force attenuates more slowly, and the mobilization of pile side frictional resistance in the upper and lower parts of the pile is more coordinated, allowing load transfer to deeper soils. In contrast, pile side frictional resistance of the large L/D piles (long length, small diameter) softens in some soil layers. For the same soil type at different burial depths, the pile-soil relative displacement required to mobilize limiting pile side frictional resistance for the same pile varies.