I do not know if CAESAR II is set to evaluate your situation. We have buried pipe and we have buoyancy calculations but we do not have buoyancy calculations for buried pipe.
Our ALA soil modeler considers pipe laid in below the water line -
you specify a soil density and also an effective soil density. The effective soil density reflects the pipe/soil interaction where water is involved. But this soil model does not lift the pipe in the buried model.
The wave load processor in CAESAR II has a buoyancy component, this will provide lift in the pipe but this is applied to a pipe under water, not in soil.