Load transfer curves from large-diameter pipe piles in silty soils at the Sakonnet River bridge

Nele Tewis, University of Rhode Island

Abstract

This manuscript presents load-transfer curves evaluated from static load tests performed on large-diameter pipe piles in silty soils. Safe and economical deep foundation design requires an accurate prediction of settlement and pile load distribution. Foundation settlement is commonly estimated using the load transfer or "t-z" method where the pile and supporting soil are modeled as a system of springs. The soil springs describe the load transfer along the pile shaft (t-z curve) and at the pile toe (q z curve). The t-z curves published for sands and clays have been derived from theory or from analysis of full-scale loading tests on slender piles. However, there are currently no t-z curves in the literature that are specifically for silts. The application of existing t-z curves to a large diameter pile in silt is uncertain because of the differences in soil behavior and possibly the effects of pile diameter. This study presents t-z curves developed from the analysis of existing load test data from two 1.8-meter diameter pipe piles in silty soil in Portsmouth, Rhode Island. Strain gage measurements were used to calculate the load distributions down the piles. One of the load distributions was adjusted for residual loads. The t-z data were directly calculated from the pile load distributions and normalized to compare them to t-z curves for sands from the literature. The developed curves show a softer load-movement response as compared to published empirical t-z curves from slender piles in sands. Using existing empirical t-z curves could lead to an inaccurate load-transfer interpretation and an underestimation of settlement. The developed t-z data compare favorably with existing theoretical t-z curves for sand but only after reducing the soil shear modulus for disturbance effects associated with installation of the pile.

Subject Area

Civil engineering

Recommended Citation

Nele Tewis, "Load transfer curves from large-diameter pipe piles in silty soils at the Sakonnet River bridge" (2011). Dissertations and Master's Theses (Campus Access). Paper AAI1500327.
https://digitalcommons.uri.edu/dissertations/AAI1500327

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