Model tests on pile tip buckling scenarios during impact driving in dense sand

Pipe piles, such as offshore monopiles, may suffer from considerable damage at the pile tip during installation because of contact with an obstacle such as a boulder or a stiff soil layer but also because of amplification of a pre-deformation or pre-dent. This damage is often referred to as pile tip buckling initiation in the former situation and extrusion buckling in the latter. This paper reports on a series of model tests carried out to verify the numerical model and understand pile tip buckling during impact driving in saturated, dense sand. The test program includes three different scenarios: tests with an initial dent at the pile tip, tests with a fixed rigid body and tests with free-moving rigid bodies (boulders) placed at a certain depth in the sand. The results show that the soil stress level strongly influences pile tip buckling. At high soil stress levels, the penetration rate of the pile decreases progressively. Notably, the wall thickness of the pile has a significant effect on the penetration curve in the case of pre-dented piles. The tests with boulders at low soil stress levels show that the buckling behavior is strongly influenced by the shape of the boulder, by the point of initial contact and by the movement of the boulder. Only small deformations can be observed at the pile tip due to the contact with a spherical steel boulder, whereas the test with the imperfectly shaped stone boulder caused considerable damage to the pile under otherwise equal test conditions. • Evaluation of model tests on pile tip buckling under various scenarios. • Performance of model behavior under increased stress levels. • Investigation of drivability in relation to pile tip buckling. • Analysis of deformation propagation due to extrusion buckling. • Collision of the pile with difference boulders during penetration.