Visualizing the penetration behavior of tapered thread piles via transparent soil: Effects of thread design

With superior construction efficiency and load-bearing performance, precast tapered thread piles hold significant potential for offshore and coastal infrastructure. However, their installation mechanics remain poorly understood, and visual experimental investigations are scarce. To address this knowledge gap, this study utilizes a developed optomechanically coupled testing system to investigate the continuous penetration process of tapered thread piles. The influence of thread design on installation behavior and load-bearing capacity was evaluated by integrating transparent soil with Particle Image Velocimetry techniques. The results indicate that minimal soil disturbance and optimal installation energy efficiency cannot be simultaneously achieved using a single thread height. Among the tested geometries, the deep thread configuration provides the highest disturbance-bearing capacity ratio, whereas the shallow thread designs maximize energy-to-capacity conversion efficiency. The shallowest thread configuration induces the lowest soil disturbance and most effectively suppress large-scale shear band propagation. Furthermore, although denser thread configurations enhance the ultimate bearing capacity, they increase both soil disturbance and installation energy consumption. Designs with pitch ratios between 0.8 and 1.2 achieve a more favorable balance among bearing capacity, installation energy, and soil disturbance than the densest configuration. This study provides fundamental physical insights into the installation mechanics and geometry optimization of tapered thread piles.