Performance of Drilled Shaft under Combined Vertical and Horizontal Loading

p–y curves have been widely used to design laterally loaded drilled shafts and driven piles, which has been a reliable and predominant method of analysis for the past few decades. Research and practice provide enriched data that have been made continuous updates possible. So far, the developed p–y curves for different soils have been successfully incorporated into numerous software to aid the design of laterally loaded drilled shafts and driven piles. However, up to date, the design of drilled shafts/driven piles cannot consider the interaction between vertical and horizontal loads, if both loads are present. Namely, vertical and horizontal loads are considered independently in the current design practice. This assumption works reasonably well when either vertical or horizontal load is the dominant one; however, if both vertical and horizontal loads are significant, the validity of the existing p–y curves under these circumstances has not been systematically verified. This research concentrates on the behavior of drilled shafts under combined vertical and lateral loads, which uses experimental and numerical approach to investigate the effect of vertical loads on a laterally loaded shaft. The experimental study involves a lab-scale test of the drilled shaft built in a test chamber. The results from the lab-scale test were then used to calibrate a numerical model that was utilized to perform the parametric analysis to study the effects of many possible factors such as drilled shaft geometry, soil friction angle, and soil stiffness. The results from this study showed that the effect of the vertical load can be significant on a laterally loaded drilled shaft, and, in general, the presence of vertical load reduced the lateral deflection. The effect of the vertical load is less salient as the length of the shaft is increased.