Axial Capacity of Piles Supported on Intermediate Geomaterials: An MPART Project

To develop empirically based guidelines for the analysis and design of piles driven into intermediate geomaterials.

Pile foundation used to support bridges must be designed and installed to sustain axial and lateral loads without failing in bearing capacity or structural damage, and without undergoing excessive settlement. The axial load-carrying capacity of a driven pile is derived from friction or adhesion along the pile shaft, and by compressive resistance at the contact of the pile base with the underlying soil. There is a well-established state of practice for evaluating pile capacity and for predicting pile driving characteristics for three material types used for subsurface materials—cohesive soil, cohesionless soils, and rock. There is a fourth type of geomaterial, however, that does not fit into one of these three basic materials types. Referred to as intermediate geomaterials, this type can have a wide array of properties with characteristics ranging from stiff or hard soil to soft weathered rock and includes shale, siltstone, claystone, and some sandstones. The axial capacity, driving resistance, and long-term resistance of piles driven into intermediate geomaterials are not well established. Intermediate geomaterials are encountered throughout Montana, and it is anticipated that a significant number of future bridge foundations will be founded in these materials, especially in the eastern part of the state. This study will develop empirically based guidelines for the analysis and design of piles driven into intermediate geomaterials. The results of this study will have the potential to improve the reliability and cost effectiveness of a significant number of future bridge foundations in the state of Montana.