Thickness Requirements

The thickness of the subbase is usually governed by the extent of frost protection desired. This is governed by subgrade type, depth of frost penetration, and availability of water near the subgrade. The thickness of the base generally depends on the degree of support required for the construction equipment and type and condition of the underlying subgrade. Thicknesses in the range of 4 to 6 inches are most common. Bases are typically extended 3 to 4 feet beyond the edge of pavement to accommodate the tracks of the paving equipment (Figure 8).