The Influence of Variable Geotechnical Parameters on the Analysis of Axially Loaded Deep Foundations Subjected to Large Deformations-PPT Presentation

PPT Presentation

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The presentation examines how variability in geotechnical stiffness affects settlement predictions for heavily loaded pile-raft foundations at a storage-tank site in Suape Port, Pernambuco, Brazil. The tanks required checks of initial and final settlement, including under the hydrostatic test specified by API 653.<br /><br />The investigation included 29 standard penetration tests, soil sampling, and laboratory classification, triaxial, and oedometer tests. Two 1,000 mm-diameter continuous-flight-auger piles were instrumented and load-tested to 10,000 kN using different loading procedures. The tests reached maximum loads of about 6,000 kN and 4,700 kN, with corresponding head displacements of 250 mm and 320 mm.<br /><br />The study assessed the influence of sand stiffness using finite-element models and Janbu’s stress-dependent modulus approach. It varied the modulus number across soil layers and compared predicted movements with load-test results. Accounting for parameter variability produced substantial uncertainty in settlement estimates; calibration against load-test data improved the coefficient of variation. The tests indicated a higher modulus number in the second layer than typical reference values.<br /><br />For design, the authors selected layer moduli based on reliability and allowable movement, then evaluated serviceability at an 80 mm settlement limit. The proposed pile-raft system used 19 piles, each 15 m long and 1 m in diameter, with the raft carrying approximately 45% of the load and the piles 55%.<br /><br />The presentation concludes that stiffness variability must be addressed when foundations operate near pile failure loads. Reliability-based assessment and full-scale load testing—particularly in coastal sedimentary soils—are essential for credible deformation predictions, and in this case the load tests were more useful for design calibration than laboratory oedometer results.

Keywords

geotechnical stiffness

pile-raft foundations

settlement prediction

Suape Port

storage tanks

API 653

load testing

Janbu modulus

reliability-based design

oedometer tests