LRFD Resistance Factors for Design of Driven Piles Using the Texas Cone Penetration (TCP) Test-Paper

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This study calibrates Load and Resistance Factor Design (LRFD) resistance factors for driven piles in soil designed using the Texas Cone Penetration (TCP) test. The work supports replacing the allowable stress design approach currently used in the TxDOT Geotechnical Manual.<br /><br />Researchers compiled full-scale load-test data from Texas and neighboring states, conducting new TCP borings at non-Texas sites. The final database included 30 precast square concrete piles. Measured ultimate capacities were interpreted using Davisson’s criterion and 5% and 10% relative-settlement criteria, then compared with capacities predicted from TCP blow counts and TxDOT design procedures. Data-quality ratings were used to weight the statistical analysis, giving an effective sample size of 26.8. Capacity biases were best represented by lognormal distributions.<br /><br />Monte Carlo simulations calibrated resistance factors for target reliability indices of 2.33 and 3.00. For the three capacity criteria, the factors were respectively 0.44, 0.47, and 0.47 at a reliability index of 2.33, and 0.30, 0.32, and 0.31 at 3.00. Although the 10% settlement criterion produced the highest mean bias, it also had greater variability, so it did not yield the highest factor in every comparison.<br /><br />The authors recommend using Davisson-based factors for LRFD design of driven piles in soil with the TCP method, given Davisson’s widespread use and the small gains from the other criteria. The recommended factors are 0.44 for a target reliability index of 2.33 and 0.30 for 3.00.

Keywords

Load and Resistance Factor Design

LRFD resistance factors

driven piles

Texas Cone Penetration test

TCP

Davisson criterion

pile load test

geotechnical design

Monte Carlo simulation

reliability index