United States Department of Transportation
i
Improving agreement between static method and dynamic formula for driven cast-in-place piles.
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2013-06-01
[PDF-7.19 MB]
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Abstract:This study focuses on comparing the capacities and lengths of piling necessary as determined with a static method and with a dynamic formula. Pile capacities and their required lengths are determined two ways: 1) using a design and computed method, such as the static method (Nordlund/Thurman/Tomlinson) identified in the Wisconsin Bridge Manual, and 2) using as-driven information, such as the Wisconsin-modified Engineering News Formula, the modified-Gates method. A collection of 182 cases was used to compare predictions made with the static method with prediction made using the Federal Highway Administration (FHWA)-modified Gates driving formula. The most effective factors influencing the agreement between predictions made by DRIVEN and FHWA-Gates were the effective stress at the tip of the pile, the friction angle for coarse-grained soils, and whether load was carried in side resistance or end bearing. Correction factors are developed to correct the static method for overburden stress at the tip of the pile. Furthermore, conditional limits are suggested for the friction angle for coarse-grained soils. Improvements were attained in the agreement for pile length required for many of the cases, however, in about 10 percent of the cases, the prediction of length of piling was not as accurate and the overall coefficient of variation increased. However, predictions of capacity at the depth driven in the field was significantly improved. Coefficients of variation for the agreement between methods improved to 0.28 from the original 0.98.
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