- Subgrade
- The natural or filled ground the pavement sits on. Its strength decides how thick the base must be. Soft, wet or uneven subgrade is usually improved by removal, replacement, drying or stabilisation before any road base is placed over it.
- CBR
- California Bearing Ratio, a measure of how strong the subgrade is. It compares the soil's resistance to penetration with a standard crushed rock. A low CBR means a weaker subgrade, so the designer specifies a thicker base or ground improvement.
- Proof-rolling
- Driving a heavy roller or truck over the subgrade to find soft spots. Areas that deflect, rut or pump under the wheels are marked and fixed before base goes on. It is a check that catches what visual inspection misses.
- Crossfall
- The sideways slope of the surface that sheds water. It is usually expressed as a percentage or ratio, and directs water to a kerb, edge or drain rather than letting it pond in wheel paths, where it softens the base.
- Geotextile
- A fabric laid on soft ground to separate and stabilise layers. It stops fine soil pumping into the base and keeps the rock from pushing down into mud. Different grades suit separation, filtration or reinforcement, so the designer specifies which.
- DGB
- Dense graded base, a crushed rock blend with sizes from coarse stone down to fines. The mix packs tightly when compacted at the right moisture. It is often ordered by its maximum stone size, such as DGB20, so confirm the product name with the supplier.