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Equivalent Granular Thickness

Equivalent Granular Thickness. 6.04 Apply the concept of Equivalent Granular Thickness to convert a layered system of different materials into an equivalent thickness of a given reference material.

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Equivalent Granular Thickness

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  1. Equivalent Granular Thickness 6.04 Apply the concept of Equivalent Granular Thickness to convert a layered system of different materials into an equivalent thickness of a given reference material. The following presentation contains references to Figure 6.04b, Table 6.02 , “GBE Example 1”, all of which are posted under subsection 2.6 of the course notes on the instructor’s website. Viewer discretion is advised as some scenes contain material of a mathematical nature.

  2. Why is the EquivalentGranularThickness concept necessary? a pavement design consists of the specification of thicknesses of layers of different materials an infinite number of combinations of these parameters are possible what is needed is one unit or parameter that characterizes the pavement’s strength

  3. Basic Theory Layered Elastic Theory is used to derive layer equivalency factors for each layer of a pavement knowing the thickness and Modulus of Elasticity of each pavement layer, an equivalent thickness of a standard reference material is calculated this equivalent thickness is used to characterize the pavement’s strength

  4. And now… Some Mental High-jinks

  5. A layered system of a reference material h1 H1 M1  Mref h2 M2 He H2 Mref h3 M3 H3 Mref A layered system of different materials is converted to… therefore and

  6. In Ontario… The elastic modulus for new granular ‘A’ is assumed to be 50,000 psi (0.345 GPa) The elastic modulus for new hot mix asphalt is assumed to be 400,000 psi (2.758 GPa) The elastic modulus for new granular subbase is assumed to be 15,000 psi (0.103 GPa)

  7. The Standard, Reference Material is NEW GRANULAR ‘A’ Therefore, in Ontario, the layer equivalency factor for new asphalt hot mix is… This means that 100 mm of new hot mix asphalt has equivalent strength to 200 mm of new Granular ‘A’

  8. right, 1.0! What would the layer equivalency factor for new granular subbase in Ontario be? In Ontario, granular ‘A’ is used for the granular base layer in conventional pavement design Therefore the layer equivalency factor for granular base is…? i.e., 300 mm of new granular subbase would be equivalent in strength to 200 mm of new granular ‘A’

  9. MTO Tabulated GBE’s (After: "Pavement Design and Rehabilitation Manual", 1990) • The MTO has published Granular Base Equivalencies (GBE’s) for three design situations: • New Projects • Resurfacing Projects • Reconstruction Projects These are listed in Table 6.02 in the course notes.

  10. New Projects • these are the maximum values to be assumed for new pavement designs Resurfacing Projects • these are the values to be assumed for existing pavement layers when an overlay is being considered • these are based on average test values on pavements overlaid by the MTO Reconstruction Projects • These are the lowest values for the materials in a pavement structure (at their weakest)

  11. GBE’s can be… • estimated during coring and boring surveys based on the operator’s descriptions of each layer material or based on an estimated percent loss in strength • calculated from measured elastic modulus values for samples of each layer of the pavement • used to evaluate the strength of an existing pavement, determine overlay requirements or design a new pavement

  12. Example: Given the bore hole log data below, evaluate the GBE of this pavement.

  13. The total GBE for the pavement is therefore: What was the original GBE for the pavement ? What % of its original strength has been lost?

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