subgrade under special condition

例句：

1. 1. Thesubgrade is a crucial part of theroad construction process.
   副级是道路建设过程中至关重要的一部分。
2. 2. The subgrade was designedto withstand heavy traffic loads.
   副级被设计来承受重交通负荷。
3. 3. Thesubgrade must be leveled and compacted before the main road is built.
   在主要道路建造之前，副级必须平整和压实。