It is considered for substructures of large bridges submerged under deep water bodies.

• A. Water Current
• B. Seismic Loads
• C. Thermal Stresses
• D. Buoyancy Effect

Answer: (D)

For submerged substructures in deep water, buoyancy is the dominant factor because Archimedes’ principle says the water surrounding the submerged volume exerts an upward force equal to the weight of the displaced water. This buoyant force reduces the effective downward load the foundation must carry, which directly affects stability, bearing capacity, and the risk of uplift. In deep water, the submerged volume can be substantial, making buoyancy a primary design consideration for caissons, piles, or other foundations to ensure they remain firmly planted and do not float or lift under hydrostatic conditions.

The other factors—water currents, seismic loads, and thermal stresses—are important in bridge design, but they are not the central effect for substructures that are largely or fully below the water surface. Currents influence lateral and wave loading, seismic effects are always relevant, and thermal effects depend on temperature differences, but buoyancy determines the core vertical force balance in deep-water substructures.