Dragload of pile groups in consolidating non-Darcian clays

Abstract

In the present study, the behaviour of pile groups with flexible cap in consolidating non-Darcian soil is investigated in terms of dragloads and downdrag. The effective stresses and the settlements are computed at different depths of the soil layers using a non-linear, one-dimensional consolidation equation for variable permeability and the non-Darcian condition. The relationship between displacements and shear stresses at the pile–soil interface and at the pile tip are modelled using a hyperbolic function. The proposed model is validated with the reported experimental results. The effects of pile spacing, slenderness ratio, soil modulus, pile modulus and the effects of non-Darcian parameters (α and n) on the developed dragload and downdrag have been studied for line pile groups (3 × 1), square pile groups (2 × 2, 3 × 3 and 5 × 5) and rectangular pile groups (3 × 2). It is observed that the central pile of a 5 × 5 pile group mobilises only about 30–45% of dragload as compared to the single piles during 1 year to 10 years of consolidation. In a 2 × 2 pile group, only 20–30% of ultimate pile settlement is attained after 5 years of consolidation owing to the non-Darcian condition, in comparison to 90% of ultimate settlement for the Darcian flow condition.