Analysis of nonlinear load-displacement behaviour of pile groups in clay considering installation effects

This paper presents an analytical approach for predicting the nonlinear load-displacement behaviour of pile groups consisting of displacement piles in normally consolidated and lightly overconsolidated clayey soils. The effects of squeezing and remolding on the soil around the piles caused by pile installation are reflected by the soil strength and shear modulus. The nonlinear load-displacement behaviour at the pile-soil interface is modeled by the load-transfer method with exponential load-transfer functions and the pile-pile interaction effects are reflected by the shear displacement method. A hybrid analytical method, incorporating the developed soil parameters and combining the load transfer method and the shear displacement method, is proposed for the problem considered. Four sets of centrifuge model tests, involving pile groups with different pile diameters, pile lengths and pile spacings, were conducted to verify the proposed analytical framework. The validity of the proposed method, the significance of the installation effects as well as the nonlinear behaviour of the pile groups are demonstrated by comparing the load-displacement curves from the centrifuge model tests with those from the proposed method and other relevant methods. Parametric studies are conducted to investigate the pile diameter, pile length, pile spacing and pile number on the stiffness efficiency of pile groups. The results indicate that increasing the pile diameter and length can effectively improve the stiffness efficiency and the load carrying behaviour of displacement pile groups.