Torpedo piles are steel, torpedo-shaped objects that are installed as projectiles penetrating the sea floor under velocity. They are a potentially viable alternative for anchoring both mobile drilling units as well as permanent facilities. However, they have not yet been used in the Gulf of Mexico. The goal of this project was to improve understanding about how torpedo piles behave during installation and pull-out by conducting 1:30 scale model tests in normally consolidated beds of kaolinite. The model torpedo piles consisted of a straight shaft with a conical tip and a load attachment at the heel (or top).
The following conclusions are drawn from this work:
- The embedment depth of a torpedo pile increases as the drop height and the weight of the pile increase, and it can be predicted accurately using a simple model for the soil resistance based on its undrained shear strength.
- The axial pull-out capacity under undrained loading after set-up increases with the embedment depth, the undrained shear strength of the soil, and the weight of the torpedo pile. The soil immediately adjacent to the shaft may be reconstituted at a higher moisture content during penetration; the predicted capacity in our model tests matches the measured capacity when an empirical side shear transfer factor, α, value of 0.5 is used in the prediction model. This zone of reconstituted soil is localized, and may not affect the mobilized side shear on the fins for a torpedo pile with fins.
- The lateral pull-out capacity under undrained loading after set-up is predicted well by a simple model that assumes the pile rotates as a rigid body in undisturbed soil.
The model test results indicate that torpedo piles do have the potential to provide a practical alternative for offshore anchors. Recommendations for further work include performing additional model tests in the laboratory and full-scale tests in the field.
