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.

Vertical-inclined alternating composite steel pipe pile(VIACP) is a new green foundation pit support technology. A numerical experimental study on the mechanical properties of vertical-inclined combination piles with different pile inclination angles and lengths was carried out with a foundation pit in Longli County, Guizhou Province, as the research object. Results demonstrate that the VIACP reduces maximum deformation by 57.8% (20.07 mm) compared to traditional cantilever piles (47.57 mm), aligning closely with field monitoring data (16.94 mm). The parametric study shows that the maximum horizontal displacement of the pile decreases and then increases as the inclination angle (5 degrees-30 degrees) increases, with the minimum displacement (20.07 mm) at 20 degrees, which is the optimum angle. Increasing pile lengths lead to progressively reduced displacements followed by stabilization while alternating long-short pile configurations exhibit synergistic effects. Mechanically, axial forces and lateral friction resistance show negative correlations with inclination angles, while bending moments adopt an S-shaped distribution along pile depth with minimal sensitivity to angle variations. Mechanism analysis highlights that the inclined piles in the structure have a pull-anchor effect, the soil between the piles together has a gravity effect, and the alternating arrangement of piles has a spatial structure effect. The three major effects increase the stiffness and stability of the support structure, which is conducive to the deformation control of the foundation pit. The research results will provide a theoretical basis for the popularization and application of the structure.

In order to study the squeezing effect of static press large-diameter single pile and piles group in layered soil, field tests of static press large-diameter pipe piles were carried out based on a project under construction, and numerical simulations of the squeezing effect of single piles and piles group were conducted using finite element software. It is shown that during the process of pile penetration, the pore water pressure in the soil surrounding the pile rapidly increases to a higher initial value. Subsequently, the excess pore pressure will rapidly dissipate and gradually stabilize. The simulated and measured values of pile top displacement show a pattern of larger displacement at the pile top when the pile is first penetrated, and smaller displacement at the pile top when the pile is penetrated later. The measured horizontal displacement of the soil layer at each observation point of the group of 7 piles showed a turning point at a depth of about 2.5 m and fluctuated with increasing depth. The measured displacement reached its maximum value between 25 and 30 m and then rapidly decreased. The finite element simulation results of squeezing effect of the group of 20 piles show that the squeezing effect around the pile is very obvious within the depth range of the pile length. The horizontal displacement of the soil below the pile length rapidly decreases, and the maximum horizontal displacement of the soil at different depths around the pile mainly occurs at the surface. In addition, the reasons for the errors between the finite element simulation values and the measured values were analyzed.