Numerical Assessment of an Imperfect Pile Group with Defective Pile both at Initial and Reinforced Conditions

Abstract

The assessment of problems of imperfect, damaged, pile groups is scarce in the geotechnical literature. Besides, techniques of assessing the performance of the foundation system once a defect is found are seldom presented, as well as real examples of the behavior of large scale imperfect foundations after their remediation. Therefore, this paper has extended the design philosophy of “piled raft” foundations to predict the numerical behavior of imperfect pile group foundations at pre and post-remediated conditions. Focus will be given to the problem of groups with either defective shorter length or lower stiffness piles, caused by natural or man-made sources. The remediation of the group is considered via added reinforcement piles with either similar or dissimilar characteristics (length, diameter, stiffness) compared to the original undamaged piles. Although the results are limited, they allow preliminary generalizations of the overall group behavior at working conditions, once a pile flaw is noticed and after the remediation has taken place. Among other results the paper highlights the load sharing mechanism between foundation elements, which relates to the position and magnitude of damage of the defective pile, as well as to the overall characteristics of reinforcement one. It was concluded that a defect caused by an unwanted pile length variation can be more detrimental to the foundation system than an unexpected low structural stiffness for the constructed pile. The derived factor of safety (SF) of the system (overall value) and of its distinct components (individual values) are also influenced by aforementioned variables, leading to questions on how the reinforcement can be made in such manner to obtain well optimized SFs. As noticed throughout the analyses, defective piles share its load with system components, once a defect appears. Nevertheless, even when imperfect such piles continue to absorb some load, although to a lesser degree than the original value. The reinforcement piles tend to absorb (or retain) some of the load spread by the defective ones, in a proportion which depends to its general characteristics (size, position, stiffness). Again, questions about an optimization procedure have to be made in order to wisely and economically use this particular observed feature on the remediation design.