Load tests and numerical modeling of CFA and driven piles in marl in Savannah, Georgia
Date
2024
Authors
Zhou, Zhihao
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Marl along the southeast coast of the US, especially in South Carolina and Georgia, is a stiff, calcium carbonate-rich, over-consolidated fine-grained soil commonly used as a bearing layer for pile foundations. However, two significant engineering challenges arise: unreliable CPT-based estimations of pile resistance and strain-softening behavior complicating the prediction of pile capacity, deformation, and load-transfer mechanisms under axial load.
Comprehensive pile load tests conducted in Savannah, Georgia, were used to improve CPT-based pile resistance estimations and develop a numerical model using load-transfer (t-z and Q-z) method for driven and Continuous Flight Auger (CFA) piles. For CPT-based pile resistance estimations, the accuracy of the original LCPC and Eslami and Fellenius methods was first evaluated. Pile load test results were then used to back-calculate the coefficients of these methods for improvement, which were subsequently verified with additional pile load test data. The main strength parameters of the load-transfer (t-z and Q-z) method model were correlated with the improved CPT methods coefficients. After calibration, the numerical model was verified using additional pile load test data. Moreover, a 3D continuum finite element method (FEM) simulation using the ‘OC Clay’ model in Plaxis 3D was conducted to capture strain-softening behavior and examine load-transfer mechanisms. The 3D continuum FEM model was calibrated and validated against separate pile load test data, and a parametric study was conducted to investigate how soil strength parameter, pile dimensions, and embedment depth into marl influence pile performance.
Description
Keywords
marl, driven pile, CFA pile, numerical simulation, T-z method, CPT correlation, 3D continuum finite element method