In TheConstructor you can ask and answer questions and share your experience with others!
The sub-grade is a pavement layer whose primary duty is to sustain the higher pavement layers and provide excellent drainage for infiltrating rainwater. Along with the other pavement layers, it must function as a single structure.
As per AASHTO soil classification see the following;
| A-1 | A-3 | A-2 | |||||
| A-1-a | A-1-b | A-2-4 | A-2-5 | A-2-6 | A-2-7 | ||
| 50 max | … | … | … | … | … | … | |
| 30 max | 50 max | 51 min | … | … | … | … | |
| 15 max | 25 max | 10 max | 35 max | 35 max | 35 max | 35 max | |
| … | … | 40 max | 41 min | 40 max | 41 min | ||
| 6 max | N.P. | 10 max | 10 max | 11 min | 11 min | ||
| stone fragments, gravel and sand | fine sand | silty or clayey gravel and sand | |||||
| excellent to good |
