Hyperbolic load-displacement analysis of helical and expanded piles: database approach

In recent years, there has been a focus on improving geotechnical systems by implementing and constructing new deep foundation such as helical and expanded piles. This study examined the effects of parameters such as embedment depth, pile geometry, and axial loading direction on the load-displacement behaviour of these piles. To conduct the research, a database was compiled consisting of 80 axial loading test records for different piles. The embedment depth of the piles ranged from 2.4 to 36.8 m, and the diameter of helices or expanded parts ranged from 254 to 1500 mm. The ultimate load of the piles was determined using the 2.5% and 5% displacement ratio criteria and the Brinch-Hansen 80% method. Additionally, hyperbolic functions were fitted to the load-displacement curves, allowing for consistent estimation of the limit load and the initial tangent modulus. Analysis of the results from the database revealed that the dominant factors influencing the ultimate load, limit load, maximum measured load, initial stiffness, and load-displacement behaviour were the ratio of helices or expanded part diameter to shaft diameter, shaft and toe surface area, and load direction. Correlations derived from the database were validated using measurements from eight full-scale helical and expanded piles.