Performance-Based Design Method for Multiple Helices of Helical Pile in Cohesionless Soil

Abstract

Multiple helices are being used frequently in helical pile applications nowadays. This paper presents multiple helices on simplified field design charts for small diameter helical piles that relate service compressive load and soil parameters as a group with the pile parameters. This study conducts an extensive three-dimensional nonlinear finite element analysis (FEA) study on multiple helices piles using the FEA program PLAXIS to evaluate helices’ performance subjected to axial compressive loads. A calibrated and verified numerical model uses full-scale load testing data of multiple helices from practical experience. This paper compiled numerical results from 495 models to propose an extension of the chart-based design. Here, the optimized combination of multiple helices will be the output of the design chart for soil type, service load, and allowable displacement as input. At the end of this paper, the design charts for double and triple helices are validated for cohesionless soil. The correlation square, R2, ranges from 0.69 to 0.86 for cohesionless soil. The mean Qc/ Qm is 0.90 for double helices and 1.04 for triple helices. Preliminary evaluation suggests that the method performs well. The authors believe that this study will permit engineers and state agencies to better understand the behavior of multiple helices, resulting in a more resilient approach in designing small diameter helical piles for a compressive load.