Granular base equivalency

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. So, to calculate the GBE, the depth of each layer should be multiplied by the granular equivalency factor for the material in that layer. In the next step the sum of the converted layer thicknesses is calculated.[2] This sum is called granular base equivalency, which is a popular and important measure in pavement design and pavement performance modeling.[3][4][5]

Profile of pavement showing the different layers of material in a certain road in Ontario. The thickness of these layers can be translated to GBE.

Example

Here is an example of GBE calculation adopted from Piryonesi (2019).[1] This example belongs to a road in the LTPP database. This road is made of the following layers: subbase, base, and three layers of hot mixed asphalt concrete. Their thicknesses are given in millimeters in the following table. The total GBE for this road 805.7 millimeters.

Layer Thickness (mm) Conversion coefficient Equivalent thickness or GBE (mm)
Hot mixed asphalt 30.5 2 61.0
Hot mixed asphalt 58.5 2 117.0
Hot mixed asphalt 38.1 2 76.2
Base 144.8 1 144.8
Subbase 607.1 0.67 406.7
Total - - 805.7

References
  1. Piryonesi, Sayed Madeh (November 2019). Piryonesi, S. M. (2019). The Application of Data Analytics to Asset Management: Deterioration and Climate Change Adaptation in Ontario Roads (Doctoral dissertation) (Thesis).
  2. Haas, R., and Kazmierowski, T. 1996. TAC's New Management Design and Management Guide. Transportation Association of Canada (TAC), Ottawa.
  3. Piryonesi, S. M.; El-Diraby, T. E. (2020) [Published online: December 21, 2019]. "Data Analytics in Asset Management: Cost-Effective Prediction of the Pavement Condition Index". Journal of Infrastructure Systems. 26 (1). doi:10.1061/(ASCE)IS.1943-555X.0000512. S2CID 213782055.
  4. Piryonesi S. Madeh; El-Diraby Tamer E. (2020-06-01). "Role of Data Analytics in Infrastructure Asset Management: Overcoming Data Size and Quality Problems". Journal of Transportation Engineering, Part B: Pavements. 146 (2): 04020022. doi:10.1061/JPEODX.0000175. S2CID 216485629.
  5. "Public Works Canada (1992). "Manual of Pavement Structural Design," Public Works Canada, Architectural and Engineering Services, Air Transportation" (PDF).
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