Estimation of Shaft and Base Responses from Pile Load Test-Paper

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The paper presents a method for estimating a pile’s shaft and base stiffnesses and ultimate resistances from initial axial pile-load-test data. The pile–soil system is idealized as a rigid pile with separate, nonlinear shaft and base responses represented by hyperbolic relationships. The measured load–settlement curve is analyzed using Chin’s method: a linear fit of settlement/load against settlement provides estimates of the pile’s ultimate load and initial stiffness. These values, together with measurements at selected settlements, are used in an iterative procedure to determine shaft and base parameters.<br /><br />The method is applied to test piles at three bridge sites on India’s NH31D. Predicted load–settlement curves agree well with the measured curves. The estimated shaft and base parameters vary substantially among sites, highlighting the influence of local soil conditions and pile installation. Estimated ultimate base resistances are broadly comparable to values calculated using IS 2911, while the code-based shaft-resistance estimates are reported to be higher in most of the comparisons.<br /><br />The authors conclude that initial load tests can be used not only to check pile capacity but also to infer the installed pile’s shaft and base responses. They suggest that compiling such results could help improve Indian design guidance. The approach relies on the assumed hyperbolic response and rigid-pile model, and its demonstrated application is limited to three test sites.

Keywords

pile load test

shaft stiffness

base stiffness

ultimate resistance

hyperbolic relationship

Chin’s method

load-settlement curve

bridge piles

soil-structure interaction

IS 2911