Resistance Factors at Serviceability Limit State Using the Texas Cone Penetrometer as the Predictive Model-Article

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The study calibrates serviceability limit state (SLS) resistance factors for deep foundations designed using the Texas Cone Penetrometer (TCP) method. It analyzes 60 full-scale load tests—33 driven piles and 27 drilled shafts—paired with TCP boring data from projects in Texas and neighboring states.<br /><br />The researchers used a load-based performance function, comparing the measured load corresponding to a tolerable settlement with the design load predicted by the TCP method. Tolerable settlements ranged from 6.35 to 25.4 mm (0.25 to 1.0 in). Biases were modeled as lognormally distributed, and resistance factors were calculated using First Order Second Moment (FOSM) and Monte Carlo simulation (MCS), for reliability indices of 2.33 and 3.00.<br /><br />Across the tested settlement limits, factors ranged from 0.33 to 0.62 (FOSM) and 0.37 to 0.67 (MCS) for driven piles, and from 0.37 to 0.77 and 0.41 to 0.86, respectively, for drilled shafts. Factors generally increased with allowable settlement. Most foundations designed using the TCP method were predicted to settle no more than 12.7 mm (0.5 in) under design load.<br /><br />The results provide SLS factors for TCP-based design, but apply only to foundations in soils and settlements up to 25.4 mm. The authors also caution that static load-test behavior may not represent service conditions in every case; additional data are needed for larger settlements and foundations in rock or intermediate geomaterials.

Keywords

serviceability limit state

deep foundations

Texas Cone Penetrometer

TCP method

driven piles

drilled shafts

load tests

resistance factors

reliability analysis

tolerable settlement