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|
|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.