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.

Cyclic loads induced by environmental factors such as wind, waves, and currents can lead to degradation in pile performance, affecting settlement accumulation and bearing capacity evolution. This paper presents a comprehensive investigation through model tests focusing on a single pile subjected to static and cyclic loading in medium-dense sands. The influence of installation method, diameter, cyclic load amplitude, and loading frequency on pile response was explored, particularly emphasizing the accumulation pattern of pile head settlement and the evolving laws governing pile shaft and end resistance. The findings illustrate that the radial stress at the pile shaft 400 mm away from the pile end increases to 3.27 times its initial stress after pile jacking. As pile diameter increases, the accumulative settlement rate decreases, highlighting the soil-squeezing effect on cyclic stability. Small cyclic loads gradually densify soil around the pile end, increasing pile end resistance, while larger cyclic loads rapidly reduce both pile end and shaft resistance. Under high-amplitude, low-frequency cyclic loading, the load-settlement hysteresis characteristics of model piles intensify, with the hysteresis loops moving more rapidly in the deformation direction.

Integrated field and laboratory characterisation of geomaterial behaviour is critical to foundation analysis and design for a wide range of offshore and onshore infrastructure. Challenges include the need for high -quality sampling, addressing natural and induced micro -to -macro structures, and applying soil and stress states that represent both in -situ and in-service conditions. This paper draws on the Authors' recent research with stiff glacial till, dense marine sand and low -to -medium density chalk, and focuses particularly on these geomaterials' mechanical behaviour, from small strains to failure, their anisotropy and response to cyclic loading. It considers a range of in -situ techniques as well as highly instrumented monotonic and cyclic stress -path triaxial experiments and hollow cylinder apparatus tests. The outcomes are shown to have important implications for the analysis of large driven piles under monotonic -and -cyclic, axial -and -lateral loading, and the development of practical design methods. Also highlighted are the needs for approaches that integrate field observations, advanced sampling and laboratory testing, numerical and theoretical modelling.

Featured Application The failure analysis of soil in the field of geotechnical engineering.Abstract The localization of deformation in shear bands is a fundamental phenomenon in granular materials like soil. In this study, we focus on the characteristics of shear bands, particularly the size effect, by implementing biaxial discrete element method (DEM) modeling. Firstly, we describe the establishment of the biaxial experimental model with dense sands. Then, we implement analyses of specimens with different sizes and find that there is a clear size effect in the stress-strain curve after the peak strength point, and there is less of a size effect in the angle of the shear band; the angle is consistent with Arthur's theory. Finally, the reason for the size effect is analyzed using the width of the shear band and the porosity inside the shear band. As the specimen size increases, the ratio between the shear band area and the whole specimen decreases. This effect reduces as the isotropic confining stress increases. The difference in the proportion of the shear band area mainly causes the size effect that affects the specimen deformation characteristics. We also find that with the increase in isotropic confining stress, the type of shear band gradually changes from cross-type to single-type. Our study provides valuable insights into understanding the behavior of granular materials.