"堆石斜坡堤" can be translated into English as "rubble mound slope breakwater" or simply "rubble mound breakwater with a sloping face".
"Rubble mound" refers to a structure made of loose, irregularly shaped stones or rocks.
"Slope breakwater" indicates a breakwater with a sloping surface rather than a vertical or stepped one.
In many contexts, especially in coastal engineering terminology, "rubble mound breakwater" is a widely recognized term that encompasses various designs, including those with sloping faces. If you specifically want to emphasize the sloping aspect, the second phrase could be used for clarity. However, the first term is more concise and commonly used.