Analyzing the Load-Transfer Behavior (T-Z Curve) for Instrumented Test Piles Driven in Clayey Soil-Paper

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The study develops an empirical shaft load-transfer (t–z) curve for driven prestressed concrete piles in clayey soils. Researchers analyzed 12 instrumented test piles installed at bridge sites across Louisiana. Vibrating-wire strain gauges measured axial load along each pile during static load tests conducted 7–14 days after driving, allowing shaft friction and relative pile–soil movement to be calculated for individual segments.<br /><br />The measured relationships were compared with established load-transfer models, including those proposed by Hirayama, Fleming, and Bohn and colleagues. The study calibrated the stiffness parameter, M, in a hyperbolic t–z equation to best fit the test results. Regression analysis produced a recommended value of M = 0.0012, lower than the comparison models’ values of 0.0025, 0.004, and 0.0038, respectively. The proposed curves showed good agreement with measured behavior and were also assessed against other pile-load-test cases.<br /><br />The authors conclude that the calibrated hyperbolic model offers a practical way to estimate shaft-friction mobilization and predict pile load–settlement response. However, its performance depends strongly on accurately estimating ultimate shaft capacity, which should reflect local soil conditions and practice.

Keywords

shaft load-transfer

t-z curve

driven prestressed concrete piles

clayey soils

instrumented test piles

static load tests

shaft friction

hyperbolic model

pile-soil interaction

load-settlement response