bottom layer of subgrade

例句：

1. 1. The engineerused a laser to create the bottom layerof the road.
   工程师使用激光创建了道路的底层。
2. 2. The construction crew was workingon the bottom layer of the foundation.
   施工队正在工作于地基的底层。
3. 3. Thenew design aims to improve the durability ofthe bottom layer of the road.
   新设计旨在提高道路底层的耐用性。