PROBABILISTIC FAILURE ANALYSIS OF PILE FOUNDATIONS

Abstract

The reliability assessment of the load-carrying capacities of piles based on static and dynamic approaches with special consideration to pre-cast concrete and steel as pile types is reported in this work. Steel and precast concrete piles were analyzed based on static pile capacity equations under various soils such as cohesive, cohesionless, and intermediate soils between sand and clay and layered soils. Likewise, three (3) dynamic formulae (namely: Hiley, Janbu and Gates) were closely examined and analyzed using the first-order reliability concept. Uncertainties are common phenomena in engineering, therefore all the interrelated variables in the carrying capacities of pile are treated as random variables with assumed practical probability density functions. The concept of the First-Order Reliability Method (FORM) is a powerful tool for estimating nominal probability level of failure associated with uncertainties and it is the method invoked for the reliability estimations in this work. Generally, piling reliability decreases as pile length increases but the rate of decrease is more rapid for concrete than steel. For precast concrete piling, pile length greater than 30m will result in catastrophe while much longer steel piles that economy will permit are admissible. Hence, steel piles are recommended as alternative materials in cohesionless soils. Likewise, the dynamic predictions of Hiley and Janbu lead to similar safety levels while Gates' results in totally different implied safety levels.