The assumed limiting performance of the five classes of backfill material defined in A1 is shown in Table NG5.1.
| Backfill material class | Material performance % CBR |
|---|---|
| A | Over 15 |
| B | 7 to 15 |
| C | 4 to 7 |
| D | 2 to 4 |
| E | Less than 2 |
Modified Type 1F Unbound Mixture is the preferred option in narrow trenches and small openings. It has a lower nominal aggregate size compared with Type 1 Unbound Mixtures, making it more resistant to segregation during transport and placement. Performance within a trench will be comparable with Type 1 Unbound Mixtures.
