subgrade bed

例句：

1. 1.The engineer designed the subgrade bed to support the weight of the road.
   工程师设计了次级路床来支撑道路的重量。
2. 2.The subgrade bed was constructed using a mixture of crushed stone and sand.
   次级路床是用碎石和沙子混合制成的。
3. 3.The subgrade bed is crucial for ensuring the stability of the road surface.
   次级路床对于确保道路表面的稳定性至关重要。