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The CBR is expressed as a percentage of the actual load causing the penetrations of 2.5 mm or 5.0 mm to the standard loads on crushed stone. A load penetration curve is drawn. The load values on standard crushed stones are 1,370 kgf (13.44 kN) and 2,055 kgf (20.15 kN) at 2.5 mm and 5.0 mm penetrations respectively.
A road of such material is called a "metalled road" in Britain, a "paved road" in Canada and the US, or a "sealed road" in parts of Canada, Australia and New Zealand. [ 48 ] A granular surface can be used with a traffic volume where the annual average daily traffic is 1,200 vehicles per day or less.
When geotextile fabric is used, a gravel layer with a minimum thickness of 6" (15 cm) [4] is suggested to ensure the fabric remains unexposed. Road construction guidelines suggest that the crown in the road surface begins at the center point in the road, and does not exceed a 4% gradation from the center to the edge of the roadway. [5]
The lower 8 in (20 cm) road thickness was restricted to stones no larger than 3 inches (7.5 cm). The upper 2-inch-thick (5 cm) layer of stones was limited to stones 2 centimetres ( 3 ⁄ 4 in) in diameter; these were checked by supervisors who carried scales.
Granular base equivalency or granular base equivalence (GBE) is a measure of total pavement thickness. [1] [2] Since pavement is composed of multiple layers with different physical properties, its total thickness is measured by GBE. GBE translates the thickness of different road layers to a number using a set of coefficients.
The subbase thickness is generally in the range of 4 to 16 inches, and it is designed to withstand the required structural capacity of the pavement section. [18] Common materials used for a highway subbase include gravel, crushed stone, or subgrade soil that is stabilized with cement, fly ash, or lime.
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Many other agencies have adopted the California pavement design method, and specify R-Value testing for subgrade soils and road aggregates. The test method states: The R-value of a material is determined when the material is in a state of saturation such that water will be exuded from the compacted test specimen when a 16.8 kN load (2.07 MPa ...