Centrifuge Modeling of Laterally Loaded Pile Groups in Improved Soft Clay

Abstract

A series of centrifuge tests were performed to investigate the behavior of laterally loaded pile groups in improved and unimproved soft clay. The soil profile consisted of four lightly overconsolidated clay layers overlying a dense layer of sand. The pile groups had a symmetrical layout consisting of 2×2 piles spaced at 3.0 and 7.0 pile diameters (D). After improving the soft clay in situ using simulated cement deep soil mixing (CDSM), pile foundations were driven into the improved ground. Centrifuge tests revealed that CDSM is an effective method to increase the lateral resistance of pile foundations. The lateral resistance of the improved pile group at 7D spacing increased by 157%. Due to pile–soil–pile interactions, the lateral resistance in the 3D pile group increased by only 112%. In both improved and unimproved pile groups with 3D spacing, the leading row of piles carried larger loads and bending moments than the trailing row of piles. No group interaction effects were observed in all pile groups with 7D spacing. At very large deflections, cracks developed and tension failure occurred in the CDSM block of the improved 3D pile group. Values for p-multipliers were back-calculated and incorporated into a computer code to perform a parametric study on improved pile groups with 3D spacing. It was seen that for CDSM block depths greater than 9D, increases in lateral resistance are practically negligible. At deflections less than 8 cm, lateral resistance of the improved pile groups is not sensitive to undrained shear strength of the improved clay representing typical cement contents.