A New SPT-Based Method for Estimating Axial Capacity of Driven Piles in Glacial Deposits

This paper proposes a new design method for the axial capacity of driven piles in glacial deposits with the standard penetration test (SPT) based on a database of 53 full-scale pile load tests. These static load tests were conducted on driven steel H and pipe piles in glacial deposits across the province of Ontario, Canada. The piles were tested in either compression and/or tension to plunging failures and had sufficient soil measurements, in particular SPT measurements, along their length for further analyses. The SPT is the most popular, and in many cases the only, field exploration technique applied in Ontario for gravel or cobble rich glacial deposits. First, the performance of existing SPT-based design methods was evaluated with the results from these pile load tests. On average, the existing design methods overestimated the measured capacity by a factor of 1.62 with a coefficient of variation (COV) of 58%. Second, a new design method was proposed according to the effective stress method to better correlate side and tip resistances with the SPT blow count (N-value). The new design method considers both the pile type and soil gradation. A set of pile load tests collected from literature were applied to validate the newly proposed method. It was found that the newly proposed design method can provide an unbiased prediction with a significantly reduced variation.