"碎砖垫层" can be translated as "broken brick cushion layer" or "crushed brick sub-base" in English.
"Broken brick cushion layer" emphasizes the cushioning effect of the broken bricks.
"Crushed brick sub-base" highlights that it is a base layer made of crushed bricks, commonly used in construction terminology.
Both translations are acceptable, and the choice may depend on the specific context or preference.