Stark Asphalt | Subgrades

Subgrade critical to overall paving life cycle.

Having the proper subgrade base for any paving project is critical to its overall life cycle. Because thickness calculations depend on the strength of the furnished subgrade, the soil must be tested prior to calculating any hot mix thickness. These tests are based on bearing capacity related to the moisture and density of the soil. The California Bearing Ratio (CBR) is one of the most widely used methods of designing pavement structures.

Poor Soil Classification - California Bearing Ratio (CBR) of 3 to 5
• silts and clays that are severely weakened by freezing and/or intrusion of water
• soils retaining high amounts of clay and fine silt
• soils with organic materials
• soils with very low permeability

Moderate Soil Classification - California Bearing Ratio (CBR) of 6 to 9
• soils that retain a moderate degree of firmness under adverse moisture conditions
• soils such as loams, silty sands, sands and gravel containing moderate amounts of clay
• soil with very low or no organic materials
• soils with low to fair permeability

Good Soil Classification - California Bearing Ratio (CBR) of 10+
• soils that retain a substantial amount of their load-supporting capacity when wet
• soils such as sand and gravel
• soils with no organic materials
• soils with fair permeability

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