Before revision: Subbase C.) Base course D.) Paver base E.) Pavers F.) Fine-grained sandIn transport engineering, subgrade is the native material underneath a constructed URL The Idiots' Guide to Highways Maintenance highwaysmaintenence.com pavement or railway track (US: railroad track).
After revision: Subbase C.) Base course D.) Paver base E.) Pavers F.) Fine-grained sand450px|Section through railway track and foundation showing the sub-gradeIn transport engineering, subgrade is the native material underneath a constructed URL The Idiots' Guide to Highways Maintenance highwaysmaintenence.com pavement or railway track (US: railroad track).