Resistance responses and design recommendations for driven piles in coarse-grained soil-based intermediate geomaterials

Piles driven in Intermediate GeoMaterials (IGM) pose multiple design and construction challenges because of the high uncertainty in IGM properties, lacking knowledge pertaining to pile responses in IGM, and absence of classification, static analysis (SA) methods, and design recommendations. A classification criterion is established for coarse grained soil based intermediate geomaterials (CG-IGM) using test pile data from bridge projects completed in four U.S. states. This study improves our understanding of pile resistance responses in CG-IGM and results in pile design recommendations. Unit shaft resistance (q_s) of CG-IGM increases with the ratio of effective vertical stress (${\sigma }_v^{\prime }$) to the ratio of corrected N-value, (N₁)₆₀. Unit end bearing (q_b) increases with the ratio of. corrected N-value, (N₁)₆₀ to the effective vertical stress (${\sigma }_v^{\prime }$). New SA methods are developed for predicting q_s and q_b. The proposed SA methods are compared against existing β-method developed for coarse grained soil and validated using an independent pile load test dataset. Pile setup is observed in q_s of piles driven in CG-IGMs, and pile relaxation is mostly observed in q_b. Statistical assessment concludes that the proposed SA methods provide more accurate and consistent q_s and q_b predictions than that by the β-method.