Okay, the user wants me to translate "sub-grade" into French. Let me think about the correct term.
First, "sub-grade" can refer to a sub-base or sub-layer in construction, like in road building. In French, the term for sub-base is "sous-couche" or "base de sous-sol". But I need to check which is more commonly used.
Alternatively, "sub-grade" might be used in contexts like grading or classification. If it's about a lower grade, maybe "sous-grade" is a direct translation. But I should verify if that's the standard term in French technical documents.
Looking up some references, in civil engineering, "sub-grade" is often translated as "sous-couche" or "base de sous-sol". However, "sous-grade" might also be used, but it's less common. The user might be looking for the most accurate technical term.
Wait, the user's previous message was "sub-grade" and the assistant responded with "sous-couche". Maybe that's the correct translation here. I should confirm if "sous-couche" is the standard term in French for sub-grade in construction contexts. Yes, that seems right. So the translation would be "sous-couche".