In coastal engineering, gravity-type caisson breakwaters traditionally depend on their own weight for stability. However, the increasing intensity of wave activity driven by climate change, such as high waves from typhoons, raises concerns about their susceptibility to sliding and overturning.
While larger caissons can enhance stability, they come with significant construction and transportation costs due to size limitations imposed by available equipment and construction conditions. An effective strategy is to connect multiple caissons to create longer structures. Unfortunately, current connection systems often fail to efficiently balance load resistance, energy absorption, and cost-effectiveness, which limits their ability to enhance breakwater stability during extreme wave events.
A research team from National Korea Maritime & Ocean University, K-BETS, and Buman Engineering Co., Ltd. has undertaken a study titled “Structural evaluation of the novel connection system between adjacent breakwater caissons.” This research introduces two innovative caisson connection systems and assesses their performance through numerical simulations.
The first system is a hemisphere connection that features a hemispherical protrusion-recess joint. This design promotes self-alignment during construction, allows for slight sliding under wave loads to absorb shocks, and helps reduce stress concentration. Finite element analysis utilizing the Continuous Surface Cap material model indicated that an 800 mm diameter hemisphere at a 2/3 embedment depth could absorb 419 kJ of energy, which is 63% more than at full embedment depth. Additionally, each 1 mm increase in diameter resulted in a maximum load increase of approximately 9.3 kN.
The second system, known as the embedded rebar connection within riprap (ERCR), incorporates voids at the joints filled with riprap and rebar. This configuration allows for controlled displacement under lower loads while resisting excessive deformation through the interaction between the rebar and riprap. Analysis using a coupled discrete element method-finite element method approach revealed that the confinement provided by the rebar and the compaction of the riprap are crucial. Specifically, 16 mm rebar was found to absorb more energy than 25 mm due to its superior ductility, and reducing voids significantly improved overall performance.
Conducting a full-scale stability evaluation under the conditions present at the Pohang coastal site (with an 18 m water depth, 7.7 m wave height, and an 11-second wave period) demonstrated that both connection systems substantially reduced sliding displacement. Notably, the 800 mm diameter hemisphere connection at full embedment depth decreased displacement by as much as 99% compared to traditional unconnected caissons.
The study “Structural evaluation of the novel connection system between adjacent breakwater caissons” features contributions from researchers Seungbok LEE, Kyeongjin KIM, Meeju LEE, Jeongho KIM, Seokmun KIM, and Jaeha LEE (the corresponding author, reachable at [email protected]). The complete text of the paper can be accessed at this link.
