Experimental and Theoretical Study on the Stability of Submarine Cable Covered by Articulated Concrete Mattresses on Flat Hard Seabed Under the Action of Currents

The safe and stable operation of submarine cables is a critical issue in offshore wind power engineering. This study presents an experimental and theoretical study on the stability of submarine cable protected by a sleeve (SCPS) with Articulated Concrete Mattresses (ACMs) protection on a flat hard seabed under current conditions. The instability modes of the SCPS–ACMs were identified, and the effects of the number of spans, cover spacing, and ACMs length on the critical instability velocity were investigated. The experimental results indicate that the primary instability mode of the SCPS–ACMs is the overall slip mode. An increase in cover spacing enlarges the exposure scale of the SCPS in the flow environment, thereby reducing the critical velocity. Employing at least two spans effectively mitigates the boundary effect induced by the flow past the SCPS at its ends, thus ensuring the reliability of the experimental model. The critical velocity is fundamentally determined by the dimensionless parameter—the ACMs coverage ratio (incorporating both the ACMs length and cover spacing). Based on the experimental results and force analysis, a theoretical equation reflecting the intrinsic relationship between the ACMs’ cover spacing and critical velocity was established. Key parameters in the equation, such as the friction coefficient, hydrodynamic coefficients (including the lift coefficient and drag coefficient), and weight distribution coefficients, were determined. Finally, the theoretical results were validated against the experimental data, showing a good agreement and verifying the reliability of the theoretical formula. The findings of this research can provide crucial support for the optimal design of ACMs protection schemes for submarine cables on the hard seabed.