Plug Heave Phenomena during Pile Installation-Paper

Paper

Pdf Summary

The paper examines plug heave—the upward movement of soil inside open-ended piles during installation—and highlights its potential to disrupt offshore construction. Excessive heave can trap pile followers, obstruct pile operations, and increase dredging requirements. Unlike suction-pile heave, the phenomenon has little coverage in industry guidance.<br /><br />Plug growth depends on how soil enters the pile, changes in volume, and the stresses acting inside and outside the pile. Installation method is crucial: static jacking can generate strong pressure differences that promote plugging, while dynamic driving generally produces less plugging because soil inertia limits those differences. However, driven piles can still experience substantial heave, particularly in dense or overconsolidated soils, where dilation and loosening may increase plug volume. Pore-pressure dissipation can also cause volume changes between hammer blows or over time.<br /><br />Field data from an offshore wind project showed that a seabed piling template can create initial heave. Preloading its mudmats displaced soft seabed soil upward through the central pile opening. Accounting for this effect substantially improved estimates of measured heave. Analyses also considered soil volume changes and dilation, though predictions remained uncertain. A separate case study produced a predicted heave range consistent with the observed value.<br /><br />The authors conclude that plug heave cannot yet be predicted accurately, but understanding its mechanisms can help designers and contractors anticipate risks. For preliminary estimates, they suggest assuming that half of the pile-wall-displaced soil enters the pile, while accounting for template effects and possible soil volume changes. Based on observed variability, applying an uncertainty factor of about 1.5 may provide a reasonable upper-bound design estimate. Further field data and research are needed.

Keywords

plug heave

open-ended piles

offshore construction

soil plugging

pile installation

static jacking

dynamic driving

offshore wind project

soil dilation

field data