Montana Department of Transportation

Malcolm “Mack” Long, Director


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Development of P-Y Curves for Analysis of Laterally Loaded Piles in Montana

Close-up showing a deep cross-section of soil.

The response of a laterally loaded pile depends on the lateral stiffness of the soil, the pile stiffness, and the interaction between the pile and the surrounding soil. A laterally loaded pile can be analyzed using different methods; among which, the P-Y method, a method of intermediate complexity and reasonable accuracy, has been widely accepted by the geotechnical engineering community. In the P-Y method, the soil reaction is replaced with a series of independent nonlinear springs, and the nonlinear behavior of the soil is represented by the P-Y curves and relating the oil reaction and pile deflection at points along the pile length. The P-Y curves are developed based on a relatively small amount of data in specific soil conditions. Their accuracy depends on the data from which the curve was developed which may or may not correlate well with soils in Montana. Consequently, the applicability of these procedures to different soil conditions is uncertain and may lead to overly conservative designs.

The research proposed will be accomplished with the following steps: 1) review the current methods for analysis of laterally loaded piles, from the most common methods (e.g., P-Y method) to the most complex, and evaluate the applicability of P-Y curves to Montana soil conditions; 2) review and prioritize soil conditions in Montana for which laterally loaded pile behavior is not well known; 3) perform a series of model-scale, instrumented centrifuge experiments on piles embedded in prioritized soils collected from different regions of Montana in the centrifuge facility at the University of New Hampshire to develop a data set capable of gaining insight into the characteristics of P-Y resistance in Montana soil conditions; 4) couple the experimental results with numerical simulations to understand the behavior of a single pile laterally loaded in different prioritized soil conditions and develop p-y curves for analysis of laterally loaded piles in Montana; 5) use the findings from previous tasks in this research to re-evaluate the performance of a laterally loaded pile from a project site located on Interstate 15 in Lewis and Clark County, MT and validate the findings of the new research.

For more information, contact Vaneza Callejas, 802-546-0217.