A print-ready summary sheet.
SN=(a1×D1)+(a2×D2×m2)+(a3×D3×m3)cap S cap N equals open paren a sub 1 cross cap D sub 1 close paren plus open paren a sub 2 cross cap D sub 2 cross m sub 2 close paren plus open paren a sub 3 cross cap D sub 3 cross m sub 3 close paren Variable Breakdown
Here's a simple example of what the spreadsheet might look like: aashto flexible pavement design excel spreadsheet
Users must provide several critical parameters to calculate the required SN: Traffic Load ( W18cap W sub 18
The difference between initial smoothness (roughly 4.2) and terminal serviceability (2.0–2.5) before major repairs are needed. Resilient Modulus ( cap M sub cap R A measure of subgrade soil strength and stiffness. Layer Coefficients ( A print-ready summary sheet
): This accounts for variability in traffic predictions and material properties. For flexible pavements, a value of is standard. 3. Serviceability Loss (
In a new cell, input the RHS (Right Hand Side) of the AASHTO equation using the cell references created above. Calculate LHS - RHS: Calculate the difference between and the result of step 3. Run Goal Seek: Go to Data > What-If Analysis > Goal Seek. Set cell: The cell containing the difference (Step 4). To value: 0. By changing cell: The "Trial SN" cell. 4. Considerations and Best Practices Reliability & S0cap S sub 0 Layer Coefficients ( ): This accounts for variability
automatically without requiring the user to manually trigger Goal Seek. 3. Layer Design & Optimization Output This section takes the calculated target SNcap S cap N and allows the engineer to input structural coefficients ( ), drainage coefficients ( ), and trial layer thicknesses ( Dicap D sub i The spreadsheet computes the .
): The lowest acceptable smoothness before rehabilitation is required (typically 2.5 for highways, 2.0 for local roads). Calculated simply as 4. Subgrade Resilient Modulus ( MRcap M sub cap R