Evaluation of the TxDOT Texas cone penetration test and foundation design method including correction factors, allowable total capacity, and resistance factors at serviceability limit state

Date

2016-08-19

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Abstract

This dissertation explores three different aspects of the Texas Department of Transportation’s Texas Cone Penetration (TCP) test and its associated foundation design charts. The first aspect has to do with the reliability of TCP data. The TCP test hammer efficiency, rod length influence on the hammer efficiency, and effect of overburden pressure on the TCP test blowcounts (NTCP) are explored. Results are compared with published correction factors for the Standard Penetration Test (SPT). The final dataset analyzed for the study, consisted of 293 TCP tests from which 135 tests were instrumented. Analyses showed a statistically significant relationship between the TCP hammer efficiency and the rod length below ground surface. Rod length correction factors (CR-TCP) and overburden correction factors (CN-TCP) were obtained factors for the TCP test.

The second topic involves a quantitative and a qualitative evaluation of the predictive validity of the Texas Cone Penetration (TCP) foundation design charts where allowable measured total capacities determined from results of full-scale load tests were compared to allowable predicted total capacities determined from TCP foundation design charts. The final dataset analyzed compiled for this study consisted of 60 full scale load testes comprising 33 driven piles and 27 drilled shafts. Allowable measured capacities were determined using strength-based and serviceability-based models. Results from analyses suggested that it is apparent that different performance assessment criteria leads to different conclusions regarding the predictive validity of the TxDOT TCP method for deep foundation design. The allowable predicted total capacity determined from the TCP foundation design charts could be considered to be reasonable based on a strength-based model, moderately over-conservative, to over-conservative according to serviceability-based models. Further, it was observed that as the level of tolerable settlement is increased, the interpretation of the TCP foundation design charts becomes even more conservative.

The third topic identifies resistance factors for the serviceability limit state (SLS) condition used in the load and resistance factor design (LRFD) of deep foundations using the results from the TCP test. The performance function was established based on load corresponding to tolerable displacement and design load. The compiled dataset consisted of a total of 60 full scale load test cases comprising 33 driven piles and 27 drilled shafts. The loads corresponding to tolerable displacements were determined using the load-settlement curves, and these loads were compared with the design load determined using the TCP test method. Resistance factors for SLS conditions were obtained for tolerable displacements using both the Monte Carlo simulation (MCS) and the first order second moment (FOSM) calibration approaches.

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Keywords

Load tests, Deep foundations, Hammer efficiency, Rod length correction factor, Overburden pressure correction factor, Texas Cone Penetration Test (TCP), Serviceability, Predicted capacity, Measured capacity, Regression analysis, Angular distortion, Settlement, SPT, ASD, LRFD

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