This paper presents the reliability assessment of free head long piles embedded in (p-y)soft clay below the water table subjected to cyclic loading of quasi-static type. It is postulated that the physical parameters used in the description of pile-(p-y)soil system are considered to be independent random variables. The response of the system in terms of maximum driving deflection yTL is considered as a function of random variables. The COV(yTL) is assessed by the First-Order Second-Moment (FOSM) Mean Value method. The applied load is considered as a variable in a discrete fashion of a deterministic type. The reliability explorations of the performance of the system are conducted in the framework of a direct reliability method. The mean value and standard deviation of the safety margin of performance MyT allow the determination of a reliability index of the performance βyT for a specific value of the applied load. In this paper the assessment of the reliability index of performance βyT and the probability of failure are conducted in terms of individual COV(each design variable) that are variables and a group of COV(all design variables) having the same value for COV(each design variable) in the presence of a deterministic load of discrete variability.
The uncertainties in the performance of deep foundations are associated with many reasons, such as the uncertainties in loads (Ditlevsen, 1981; Ruiz, 1986; Tandjiria et al., 2000), spatial distribution of soil parameters that vary in a random fashion depending on the specific site (Ruiz, 1984; Phoon and Kulhawy, 1999a), limitations connected with a soil site exploration program, inconsistency in various testing methods, as well as uncertainties in the soil-structure interaction model (Phoon and Kulhawy, 1999b). The quantification of the uncertainties that are intrinsically connected with each cause is important, since they reflect on the behavior of the system.