Drainage Coefficient Of Subbase Using Structural Number Calculator

Drainage Coefficient Formula:

\[ M_n = \frac{SN_3}{a_n \times T_a} \]

Structural Number for Subbase Course (SN₃):

Layer Coefficient (aₙ):

unitless

Actual Thickness Base Course Payment (Tₐ):

Drainage Coefficient (Mₙ):

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1. What is the Drainage Coefficient?

The Drainage Coefficient (Mₙ) is a value assigned to a pavement layer that represents its relative loss of strength due to drainage characteristics and exposure to moisture saturation. It quantifies how effectively a pavement layer can drain water and maintain its structural integrity under varying moisture conditions.

2. How Does the Calculator Work?

The calculator uses the Drainage Coefficient formula:

\[ M_n = \frac{SN_3}{a_n \times T_a} \]

Where:

\( M_n \) — Drainage coefficient (unitless)
\( SN_3 \) — Structural Number for Subbase Course (mm)
\( a_n \) — Layer Coefficient (unitless)
\( T_a \) — Actual Thickness Base Course Payment (mm)

Explanation: The formula calculates the drainage coefficient by dividing the structural number of the subbase course by the product of the layer coefficient and the actual thickness of the base course payment.

3. Importance of Drainage Coefficient Calculation

Details: Accurate drainage coefficient calculation is crucial for pavement design as it helps engineers account for moisture-related strength reduction in pavement layers. Proper drainage design ensures longer pavement life and better performance under various environmental conditions.

4. Using the Calculator

Tips: Enter the structural number for subbase course in mm, layer coefficient (unitless value representing material strength), and actual thickness of base course payment in mm. All values must be positive numbers greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical range for drainage coefficient values?
A: Drainage coefficient values typically range from 0.4 to 1.2, with higher values indicating better drainage performance and less strength loss due to moisture.

Q2: How does drainage coefficient affect pavement design?
A: The drainage coefficient directly influences the required thickness of pavement layers. Lower drainage coefficients require thicker layers to compensate for strength loss due to poor drainage.

Q3: What factors influence the layer coefficient?
A: Layer coefficient depends on material type, quality, compaction, and structural properties of the pavement material.

Q4: When should drainage coefficient be considered in pavement design?
A: Drainage coefficient should always be considered in areas with high rainfall, poor drainage conditions, or where pavement layers are frequently exposed to moisture.

Q5: Can this calculator be used for all pavement types?
A: This calculator is specifically designed for flexible pavements with granular base and subbase courses. Different formulas may be needed for rigid pavements or other pavement types.