- The exposed subgrade (excavated to trial subgrade level or footpath depth) shall be tested by using a Scala Penetrometer for compliance with the following CBR values:
- In footpath and traffic island infill: CBR value >7 (3 blows/100mm)
- In vehicle crossing and kerb and channel areas: CBR value >10 (4 blows/100mm)
Scala penetration results shall be converted to CBR utilising Austroads 2008 Guide to Pavement Design Fig: 5.3.
- If the material fails this initial test then either:
- The existing subgrade shall be further compacted if the material is suitable, to improve the CBR value.
- The unsuitable material shall be excavated and removed from site, and replaced suitable granular fill compacted up to the trial subgrade level.
- When treatment b-ii) is required, the excavation shall extend 100mm past either side of the edge boards, or the outer limits of the construction area:
- The depth and extent of this subgrade excavation shall be as instructed by the Engineer.
Small pockets of material may require treatment rather than the entire subgrade area.
- All backfill shall be compacted in lifts of not more than 100mm.
- The subgrade area, either existing or reinstated, shall be trimmed and shaped to accommodate the specified lines and levels given and compacted to provide uniform support for the pavement course.
- All tree roots found in the subgrade or pavement area during excavation shall be removed. They shall be severed 500mm outside the final edge alignments, removed from site and legally disposed of. Any root greater than 50mm in diameter is to be cleanly sawcut. No such roots shall be cut without the prior approval of the Engineer if they are within the drip line of the tree.
Definitions in this section