Structural Number for Subbase Course Calculator

Structural Number Formula:

\[ SN3 = (a_n \times T_a \times M_n) \]

Layer Coefficient (aₙ):

unitless

Actual Thickness Base Course (Tₐ):

Drainage Coefficient (Mₙ):

unitless

Structural Number for Subbase Course (SN3):

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1. What is the Structural Number for Subbase Course?

The Structural Number for Subbase Course (SN3) represents the ability of the subbase course to withstand axle loads in pavement design. It's a numerical value that quantifies the structural capacity of the subbase layer in flexible pavement systems.

2. How Does the Calculator Work?

The calculator uses the Structural Number formula:

\[ SN3 = (a_n \times T_a \times M_n) \]

Where:

\( a_n \) — Layer coefficient (represents material strength)
\( T_a \) — Actual thickness of base course payment (mm)
\( M_n \) — Drainage coefficient (accounts for drainage characteristics)

Explanation: The equation multiplies the material strength coefficient by the actual layer thickness and adjusts for drainage conditions to determine the overall structural capacity.

3. Importance of Structural Number Calculation

Details: Accurate Structural Number calculation is crucial for pavement design, ensuring adequate load-bearing capacity, proper drainage performance, and long-term durability of the pavement structure.

4. Using the Calculator

Tips: Enter the layer coefficient (typically 0.08-0.15 for granular materials), actual thickness in millimeters, and drainage coefficient (typically 0.8-1.2). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical range for layer coefficients?
A: Layer coefficients typically range from 0.08 to 0.15 for granular subbase materials, depending on material quality and compaction.

Q2: How does drainage coefficient affect the structural number?
A: The drainage coefficient accounts for relative strength loss due to moisture conditions. Lower values indicate poorer drainage performance.

Q3: What units are used for thickness measurement?
A: Thickness is typically measured in millimeters (mm) for precise pavement design calculations.

Q4: Can this formula be used for other pavement layers?
A: Similar formulas exist for different pavement layers (base course, surface course) with appropriate coefficients for each layer type.

Q5: How does structural number relate to pavement performance?
A: Higher structural numbers indicate greater load-bearing capacity and longer pavement service life under traffic loading.