Reliability assessment of pile groups in sand

According to the U.S. Army Corps of Engineers statistics, over 40% of the inland navigation structures are more than 50 years old, and the demand for rehabilitation must be selectively invested to maximize navigation benefits. Evaluation and assessment of existing structure can play a significant role in reducing the likelihood of unexpected failures. However, current evaluation and assessment methods of pile foundation components and pile groups, that are required to maintain system integrity during normal and sever operational conditions, are based on the use of factor of safety or safety margin. They allow certain reductions in the strength based on the subjective judgement and experience of the designers.; The primary objective of the dissertation was to develop a probability-based reliability assessment methodology for single piles and pile groups as a system under lateral loads in sandy soil. The effects of soil nonlinearity, pile-soil-pile interaction (pile group effect), and pile cap flexibility on the strength and serviceability performance functions were investigated in the dissertation.; The development of a reliability assessment methodology to assess pile foundations under lateral loads required defining the modes of failure for single piles and pile groups, analytical models that can be used to predict the pile behavior, probabilistic characteristics of basic random variables used in the design, and reliability analysis methods.; Winkler solution, that models the soil response using nonlinear springs, was used to represent single piles with appropriate P-Y curves. Two analytical methods were modified to account for the pile-soil nonlinearity and pile group effect, i.e., the modified nondimensional method and stiffness method. The proposed methodology for reliability assessment was based on the stiffness method with rigid and flexible analysis of the pile cap using several reliability methods. The reliability methods used in the study are the (1) advanced second moment (ASM) method; (2) Monte Carlo simulation (MCS) method; and (3) importance sampling simulation (ISS) method. The pile group system reliability, by accounting for system redundancy due to the occurrence of partial failure of the system components, was also studied and developed.; The methodology demonstrated that the failure of pile groups, consisting of flexible piles in sandy soil under lateral loads, can be attributed to either excessive lateral deflection of the pile cap or yielding moment of average piles of respective rows in a group. The yielding moment is most likely to be reached before the full mobilization of the ultimate soil resistance. The proposed assessment methodology based on probabilistic analysis provides an easy and a more realistic approach than the current safety margin method and can accurately evaluate pile foundations by considering the uncertainties involved in loads, strength variables, and prediction models.