Aashto Flexible Pavement Design Excel: Spreadsheet

Assume three layers:

Required SN = 4.5 (example).

First, compute SN₁ = a₁ × D₁_min (D₁_min from structural or min construction – say 2 inches).
If SN₁ alone insufficient, add base: aashto flexible pavement design excel spreadsheet

SN₂_required = SN_total - SN₁

Then: D₂ = SN₂_required / (a₂ × m₂) Assume three layers:

Then check subbase similarly. Use =CEILING() to round up to 0.5 inch.

| Parameter | Typical Range | Excel Cell Example | | :--- | :--- | :--- | | Reliability (R%) | 50% - 99.9% | B4 = 90 | | Standard Deviation (So) | 0.35 - 0.50 | B5 = 0.45 | | Initial PSI | 4.2 – 4.5 | B6 = 4.2 | | Terminal PSI | 2.0 – 2.5 | B7 = 2.5 | | ΔPSI | (Initial – Terminal) | B8 = B6 - B7 | | Resilient Modulus MR (psi) | 3,000 – 30,000 | B9 = 5000 | | 18-kip ESALs (W₁₈) | 10^4 – 10^7 | B10 = 2.5E6 | Required SN = 4

The spreadsheet is programmed to solve the AASHTO 1993 Design Equation. This equation relates the number of load applications a pavement can withstand to the structural capacity required.

Given required SN, a spreadsheet calculates thicknesses but does not optimize cost (e.g., thicker base vs. thicker asphalt). Engineers must manually iterate.

Create a VBA button:

Sub SolveForSN()
    Range("A22").GoalSeek Goal:=0, ChangingCell:=Range("A20")
    MsgBox "Required SN = " & Round(Range("A20").Value, 3)
End Sub

Let’s walk through how to construct this masterpiece.