In this Letter, we propose a unique bilayer design of phononic crystal slabs that are
constructed by two layers of snowflake phononic crystal plates connected by a honeycomb
array of cylinders. By tuning orientations of snowflake-shaped holes in both layers, we
achieve two kinds of valley-projected topological elastic insulators distinguished by
conventional and layer-polarized topological valley Hall phases. Then, between different
conventional and layer-polarized topological valley Hall phases, two kinds of edge modes …