Development of Experimental P-Y Curves from Centrifuge Tests for Piles Subjected to Static Loading and Liquefaction-Induced Lateral Spreading-Article

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The study uses five centrifuge tests of pile-supported wharves to investigate pile behavior under static loading and earthquake-induced liquefaction and lateral spreading. Unlike many earlier studies, the tested piles experienced both kinematic loads from moving soil and inertial loads from the wharf deck.<br /><br />Researchers back-calculated static and dynamic soil-reaction curves (p-y curves) from pile strain, displacement, and pore-pressure measurements, then compared them with American Petroleum Institute (API) sand curves. For static loading, API curves represented ultimate soil resistance reasonably well, but their initial stiffness was generally too high. Using reduced subgrade-reaction moduli improved predictions of bending-moment profiles and other pile responses. The recommended moduli were 3,500 kN/m³ for loose and dense sand and 5,200 kN/m³ for rockfill.<br /><br />Liquefaction substantially reduced soil resistance in loose sand. The authors found that this softening could be represented in pseudo-static pile analyses by applying a p-multiplier related to excess pore-water-pressure ratio, Ru: Pm = 1.2 − 1.1Ru when Ru > 0.2, and Pm = 1.0 when Ru ≤ 0.2. The approach simplifies complex dynamic behavior, including transient resistance spikes associated with sand dilation.<br /><br />Analyses using the modified API curves and Ru-based multipliers reasonably reproduced measured peak pile bending moments across the tests; predicted values averaged about 5% above measured values. The findings support this practical method for estimating pile demands in liquefied granular soils under combined spreading and structural-inertia effects. However, the conclusions are based on sand centrifuge tests, and their applicability to soils such as sandy or low-plasticity silts requires further investigation.

Keywords

pile-supported wharves

centrifuge tests

liquefaction

lateral spreading

p-y curves

API sand curves

pile bending moments

subgrade-reaction modulus

excess pore-water pressure

p-multiplier