Effects of Vibratory Driving of Monopiles on Soil Conditions and Their Cyclic Lateral Load Bearing Behavior-Paper

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The study examines how vibratory installation affects the soil around monopiles and their subsequent lateral response under cyclic loading. Researchers conducted 1-g model tests in saturated dense Berlin sand, comparing two vibratory installation modes—cavitational and non-cavitational—with impact driving. Instrumentation measured pore-water pressure, radial earth pressure, pile penetration, bending, and lateral displacement.<br /><br />Installation produced distinct soil responses. Vibratory driving increased excess pore-water pressure, with the greatest rise during non-cavitational vibration; impact driving generated less accumulation. Impact driving caused the largest peak changes in effective radial stress, while the cavitational vibratory test had slightly higher peak stresses than the non-cavitational test. After installation, however, the non-cavitational pile had the lowest radial stresses. Stress reduction around the shaft was strongest for the impact-driven pile, consistent with friction fatigue.<br /><br />In initial monotonic lateral loading, the impact-driven pile was slightly stiffer than the vibratory-driven piles. The cavitational pile behaved similarly to the impact-driven pile, while the non-cavitational pile was softer and had lower lateral capacity. The impact-driven pile also showed greater restraint at the toe.<br /><br />Under cyclic lateral loading, installation-related differences diminished rapidly. Displacement accumulation was concentrated in the early cycles: results for all three piles became nearly identical after roughly 10–100 cycles, indicating stabilization or “shakedown” of the pile–soil system. The non-cavitational pile remained somewhat softer after the first loading package, but its cyclic response also converged with the others.<br /><br />The results suggest that installation method affects initial soil conditions and monotonic lateral behavior, but has a much smaller influence on accumulated displacement after repeated cyclic loading. Because the findings are based on scaled model tests, further research is needed before drawing general conclusions.

Keywords

monopile

vibratory installation

cyclic loading

soil response

pore-water pressure

radial earth pressure

impact driving

lateral response

Berlin sand

shakedown