Calibration of Region Specific Gates Pile Driving Formula for LRFD

This research project proposes new Louisiana Department of Transportation and Development (DOTD) pile driving formulas for pile capacity verification using pile driving blow counts obtained at either end-of-initial driving (EOID) or at the beginning-of-restrike (BOR). The pile driving formulas were developed using a regional database containing 252 static load tests and 934 dynamic load tests (DLT) collected from DOTD projects. The DLTs were conducted on blow counts taken at EOID (183 Case Pile Wave Analysis Program (CAPWAPs)) and BOR (751 CAPWAPs). The pile driving formulas were developed by conducting a nonlinear regression analysis of the generic Gates formula. The Load and Resistance Factor Design (LRFD) resistance factors (ɸ) were calibrated using the Monte Carlo Simulation (MCS) method for the Strength I limit state with a reliability index (βT) of 2.33 as recommended for pile groups in American Association of State Highway and Transportation Officials (AASHTO) specifications. The current LADOTD pile driving formula (Federal Highway Administration (FHWA) Gates Formula) used to evaluate blow counts taken at EOID was evaluated; results show a best fit ratio of 0.80 with a resistance factor of 0.67—higher than the AASHTO specifications resistance factor (ɸ) of 0.40 for the same pile driving formula. The new EOID LADOTD Modified pile driving formula has a best fit ratio 0.91 with a resistance factor of 0.59. This study recognizes pile capacity setup can significantly affect pile driving formulas ability to predict pile capacity when using blow counts obtained at BOR. Pile capacity setup was evaluated by computing the Skov-Denver pile setup factors (AQ) using total pile capacity (Q). A minimum of two pile setup categories (A and B) were identified in Louisiana. Pile setup category A is located in the coastal marshes along the gulf coast of Louisiana with setup factors (AQ) ranging from 0.135 to 0.428. Pile setup category B was assigned to the remainder of the state with AQ pile setup factors ranging from 0.021 to 0.108. An evaluation of the pile setup curves using the Skov-Denver model indicates that more than 90% of the long-term pile capacity (load test conducted at t = 14 days) can be obtained at t ≥ 6 days for pile setup category A and t ≥ 3 days for pile setup category B. A BOR pile driving formula was developed for setup category A with restrikes conducted at t ≥ 1 days with a best fit ratio of 0.93 and a corresponding resistance factor (ɸ) of 0.64. A different BOR pile driving formula was developed for pile setup category B with restrikes conducted at t ≥ 1 days with a best fit ratio of 0.92 and a corresponding resistance factor (ɸ) of 0.605. Recommendations on the implementation of these EOID and BOR pile driving formulas have been included in this study.

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