Uncertainty of p-y Curve Parameters for Laterally Loaded Driven Piles in Soft Clays

One of the design checks for driven piles is the pile lateral deflection due to lateral forces and moments. In the Indonesian practice, the pile lateral deflection is limited to 25mm to minimize the pile structural demands during strong earthquakes. This paper evaluates the field performance of laterally loaded driven piles, and is a continuation of previous studies by the authors. Twenty-nine driven concrete spun piles from three projects were laterally loaded according to ASTM D 3966-07, and the maximum lateral load was gradually applied in four cycles to 200% of the design lateral capacity. Subsequently, the test results were back-analyzed using the computer program LPILE. For each case, a trial-and-error process was conducted using a set of LPILE p-y curve input parameters to match the LPILE results with the actual pile load versus lateral deflection data. The required LPILE p-y curve input parameters were then evaluated. The first finding was that soft clays not subjected to any ground improvement measures appeared to be modelled better using the p-y curves for soft clays, while soft clays subjected to ground improvement measures appeared to be modelled better using the p-y curves for stiff clays with free water. New S_u−Sug based correlations for estimating the strain level ε₅₀ and the initial stiffness K_Sug are proposed. The uncertainty of these correlations was also examined.

Keywords: Driven piles, Laterally loaded piles, Pile load tests, Soft clays, p-y curves, Preloading, Uncertainty.