Lateral Performance and p-y Curves for Large-Capacity Helical Piles Installed in Clayey Glacial Deposit

The lateral performance of large-capacity helical piles is of significant interest. This study presents the results of five full-scale lateral load tests conducted on 6.0 and 9.0 m large-capacity helical piles of shaft diameter 324 mm and installed in structured cohesive soil. The piles were either single or double helix, with inter-helix spacing of 1.5 and 3.0 times the helix diameter, instrumented with strain gauges. The shorter piles were tested under a short-term condition, whereas longer piles were tested under a long-term condition. The soil’s p-y curves and its initial modulus of subgrade reaction were back calculated from the strain measurements and were compared with the subgrade modulus estimated from the properties of the undisturbed soils. The pile installation had a significant effect on the subgrade modulus. The number of helices and the inter-helix spacing ratio had minimal influence on the mobilized load deflection at pile head and soil resistances. A reduction factor for the initial subgrade modulus was introduced to be incorporated in design.