Behaviour of pile groups with defective piles

This paper presents analyses for response of single piles with defects, and of pile groups containing defective piles. Consideration is given to the influence on load-settlement behaviour of both structural defects (such as “necking” of the pile) and geotechnical defects (such as softened soil below the pile base). For single piles, the presence of defects leads to a reduction in pile head stiffness, and the possibility of reduced load capacity. If failure of the pile occurs because of a structural defect, there is a sudden and dramatic increase in settlement. With geotechnical defects, the apparent loss of load capacity is characterised by a more gradual increase in settlement with increasing load. For each type of defect, typical relationships have been developed, for a single pile, between the reduction in stiffness, the extent of the defect, and the applied load level. These relationships have then been used to examine the behaviour of a typical six-pile group containing defective piles. The ability of the group to redistribute the pile loads from defective to intact piles results in a less severe reduction in axial stiffness than is the case for a single defective pile. However, the presence of defective piles will generally lead to the development of lateral deflection and rotation of the group, and induces additional bending moments in the piles, even under purely axial applied loading.