Reliability studies of bored concrete pile foundations

There is a growing tendency to base the design of nuclear power plant structures on reliability criteria. In addition, even when conventional code specifications are followed, questions concerning the reliability of the system often arise. The paper presents results of ongoing studies aimed at the determination of the probability distribution of the global strength of bored pile foundations. The analysis resorts to a model in which the piles are represented as series of axially stressed elements, or 'links'. The parameters used in the model were determined from data available in an extensive experimental program that involved the measurement of the compression strength of about 3000 concrete core samples. The first part of the study deals with the evaluation of various parameters, such as depth and age, on the strength of 'in situ' concrete. The properties of concrete are then used in conjunction with the pile cross-sectional dimensions to obtain the strength distribution of a pile 'link'. In a second stage, the global strength probability distribution of a foundation system with a large number of piles is calculated by simulation. The influence of instability effects, which could lead to tilting of the entire foundation, is examined. (orig.)