Reliability of Vertical Ultimate Bearing Capacity of Foundation Pile Based on KL Expansion

To investigate the influence of soil spatial variability on the bearing characteristics and reliability of foundation pile, a numerical model of vertical foundation pile in spatial soils is developed. The KL-FORM is employed to analyze the reliability of foundation pile for the ultimate limit state of bearing capacity, which verifies the feasibility of determining the number of optimal expansion terms according to the global variance relative error. The influence of the spatial variability of soil undrained shear strength S_u and elastic modulus E on the reliability index of vertical foundation pile is analyzed. The results show that the cohesive strength of pile-soil interface should be considered as a variable which varies with the discrete value of S_u in the numerical simulation; the trend of the foundation pile resistance and pile top displacement curve is affected by the spatial variability of E, while the ultimate bearing capacity and reliability index is constant; the reliability index decreases with S_u of coefficient of variation and vertical autocorrelation distance; and when the discrete accuracy is determined, the effect of exponential and square exponential autocorrelation functions on the reliability index is negligible, but the computational cost of the latter is significantly smaller.