Open-ended pipe piles (OEPPs) are widely used in offshore foundations, yet accurately predicting their driving responses remains challenging due to soil plug complexities. Existing pile driving analysis models inadequately characterize the effects of soil plug, potentially leading to driving problems such as hammer refusal, pile running, and structural damage. This paper proposes an effective soil plug (ESP) model for OEPP driving analysis. The ESP model considers the effective range of soil plug, which exerts internal resistance that increases exponentially with depth while the beyond of effective range contributes only mass inertia. It also accounts for the relative slippage at the pile-soil plug interface. A differential iterative method is developed to solve the ESP model. Subsequently, investigations including the model validation and parameter analysis are conducted. Model validations against existing models and field measurements confirms the reliability of the ESP model. Parameters sensitivity analysis reveals the importance of soil plug length and distribution type of internal resistance on the pile dynamic responses. In addition, if soil plug slippage occurs, the displacement peak of soil plug increases with depth rather than one-dimensional wave attenuation. Furthermore, contrary to previous assumptions of continuous slippage, the soil plug experiences a discontinuous jump-sliding mode under long-duration impact loading. These findings provide theoretical basis for OEPP driving simulation and interpretations of high-strain dynamic test.

Inspired by the anisotropic shear behavior of the snakeskin, an innovative suction caisson with a bio-scale sidewall of the snakeskin is proposed, which is called the scale suction caisson (SSC). Compared with traditional suction caisson (TSC), the interface friction decreases when the SSC penetrates to the seabed, but increases as the SSC is pulled out. Therefore, the SSC has better installation and service performance than the TSC. The model tests are carried out to investigate the penetration behaviors of the SSC. The study shows the penetration resistance depends on the aspect ratio of the bio-scale surface, and the corresponding value increases with increasing the diameter of bio-snakeskin surface D1, but firstly decreases and then increases with increasing the height of bio-scale surface H1. More sand bypasses the end of the sidewall into the SSC and the sand inside the SSC is loosened under the seepage, causing the soil plug inside the caisson. In the half-caisson model tests, the soil heave inside the caisson under the different penetration depths is captured with an HD camera, and the permeability coefficient k can be further calculated. Considering the variation of the permeability coefficient k, a method of calculating the critical suction is provided.

Open-ended pre-stressed high-strength concrete (PHC) pipe piles are susceptible to progressive distortion and even failure in the vicinity of the pile toe during driving into stiff soil or rock strata. This paper presents an experimental investigation conducted as part of a power plant construction in Huainan, China. After 50 piles were driven in the initial phase, the toe of 9 piles were detected as damaged using the sonic echo testing method. In the second construction phase, four piles were instrumented with longitudinal and circumferential fiber optic cables, as well as discrete strain gauges. The recorded responses of pipe piles throughout their driving process are analyzed to reveal the causes of damages. The results show that a maximum circumferential tensile stress developed at a distance of 1/6 pile length above the pile toe, with its value three times greater than that in other cross-sections. This high circumferential stress results in transverse cracks and the failure of open-ended PHC piles and is believed to be related to the formation of soil plugs. The findings provide valuable insights into performance evaluation of driven open-ended PHC piles.