Torpedo pile penetration by combined water jet and mechanical vibrations in cohesive sedimentary beds

The penetration efficiency and safety of piles on the seabed affect the cost of offshore structures and the reliability of relevant equipment, which entails to the success or failure of the development and utilization of ocean resources. However, the traditional methods of pile penetration, including pressing method, impact driving method and vibro-driving method, are difficult to adapt to the complex marine environment. In this study, the torpedo pile penetration in cohesive sedimentary bed was investigated by applying downwardly directed vertical water jet and mechanical vibrations. The experimental work was developed in the laboratory through a series of pile penetration tests in different types of cohesive sediments. During the penetration processes of the torpedo pile, the relevant influencing factors such as water content of cohesive sediment, vibration intensity and water jet velocity were considered. The experimental results show that the penetration depth of the torpedo pile increases with the increase of water jet velocity, vibration intensity and water content of cohesive sediment. Based on the dimensionless analysis and data regression, a formula for the critical penetration depth of the torpedo pile in cohesive sediment is proposed, which is correlated with the water jet velocity and vibration intensity, as well as the torpedo pile and soil properties. In addition, the formula is verified by the experimental data of other study, which presents good consistency.