gravel stratum

例句：

1. 1. The geologist found a gravel stratum that was rich in minerals.
   地质学家发现了一个富含矿物的砾石层。
2. 2.The engineer used the data to design a new road with a smoother gravel stratum.
   工程师利用这些数据设计了一条新路，其砾石层更加平滑。
3. 3.The construction crew worked tirelessly to level the uneven gravel stratum before starting the excavation.
   施工队努力不懈地平整不均匀的砾石层，然后开始挖掘。