Evaluation of End Bearing of Driven Steel H-Piles in Intermediate Geomaterials Based on Spherical Cavity Expansion Methods

Due to shallow bedrock strata, steel piles driven in the Rocky Mountain regions are often driven in Intermediate GeoMaterials (IGMs) which are transitional geomaterials between soil and rock. Piles driven in IGM have possessed many design and construction challenges due to high uncertainty in the engineering properties of IGM, and absence of analytical quantifications. It is crucial to understand the end bearing of driven piles to ensure the stability and safety of structures, especially in Intermediate Geomaterials (IGMs). With its analytical solutions and advancements, the cavity expansion method (CEM) offers a powerful tool for analyzing end bearing of piles in various geomaterial conditions. Determining the end bearing of piles using cavity expansion theory hinges on estimating the limit pressure, which is the maximum pressure required to enlarge a spherical influence in the geomaterial around the pile tip. This study evaluates the end bearing of steel H-piles driven into siltstone for nine bridge projects in the states of Wyoming, Idaho, and Montana. The analysis was conducted based on a spherical undrained cavity expansion theory using the Mohr-Coulomb Yield criteria. The estimated end bearings based on CEM were compared with end bearings determined from full-scale static load tests (SLT) for two test piles and dynamic (DLT) pile load tests for nine test piles. The predicted end bearings considering the shape factor are 20% lower than the measured end bearings from static and dynamic load tests. On the other hand, the predicted end bearings without the shape factor are 40% lower than those from load tests. The study revealed that the radius of plastic zone decreases with the increase in undrained shear strength (su). Expanding cavity pressure increases with su and decreases gradually when the ratio of expanded to initial cavity radius exceeds 1.8.