Agencies typically specify that the subgrade must be adequately compacted to a point near its maximum density, usually:

The specification that the subgrade must be adequately compacted to a point near its maximum density is crucial for the overall stability and durability of the pavement structure. A compaction level of 95% or higher is generally recommended as it signifies that the subgrade has reached sufficient density to provide a solid base for the layers above, minimizing the potential for settlement or deformation under load.

Achieving 95% compaction implies that the soil has been compressed adequately to reduce air voids and enhance strength. This level of compaction ensures that the subgrade can effectively support the weight of the hot mix asphalt and resist the stresses imposed by traffic over time. Properly compacted subgrade also helps reduce moisture infiltration, which can lead to weakening of the base layers.

Compacting the subgrade to this level significantly contributes to the overall performance of the HMA pavement, providing better structural integrity and longer service life. It's a standard practice adopted by agencies to ensure that pavement designs perform as intended.