What Is the Pavement Subgrade Modulus of Reaction (k-value) Calculator?
Rigid concrete pavement slab design (AASHTO, PCA, FAA) requires the Westergaard modulus of subgrade reaction (k-value) representing foundation support stiffness.
Because plate bearing tests are expensive and time-consuming, engineers correlate k-values from laboratory California Bearing Ratio (CBR) or Resilient Modulus (MR).
This calculator correlates soil CBR to Resilient Modulus (psi and MPa) and computes the effective Westergaard subgrade k-value (pci and MPa/m).
How Does the Pavement Subgrade Modulus of Reaction (k-value) Calculator Work?
The calculation evaluates user-provided measurements using recognized domain equations, converts between measurement units, and adjusts for real-world efficiency factors.
Pavement Subgrade Modulus of Reaction (k-value) Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
MR is resilient modulus, k is modulus of subgrade reaction in pounds per cubic inch, and k_SI is modulus in megapascals per meter.
How to Use the Pavement Subgrade Modulus of Reaction (k-value) Calculator
- Enter your primary measurements in the input fields above.
- Select your preferred units (e.g. metric or imperial) if applicable.
- Review or adjust operational assumptions such as field efficiency.
- Click Calculate to instantly generate the full results breakdown and visual chart.
- Use the Reset button at any time to clear the form and test a new scenario.
Step-by-Step Example Calculation
Highway Subgrade Silt Soil
Input Values:
Understanding Your Result
Your calculated result represents the realistic operational capacity or baseline output under the specified conditions. Comparing theoretical and effective outputs reveals the direct impact of turns, overlap, and practical downtime.
Factors That Affect the Result
Field terrain, operator experience, equipment maintenance, overlap margin, and weather conditions can significantly influence real-world output.
When Should You Use This Calculator?
Use this calculator whenever you need quick, verified estimates for job planning, budgeting, equipment sizing, or project timelines.
Assumptions & Limitations
- AASHTO correlation: MR (psi) = 1500 · CBR for fine-grained soils (CBR ≤ 10).
- Westergaard k-value correlation: k (pci) ≈ MR (psi) / 19.4 per PCA / AASHTO Guide.
- Conversion: 1 pci = 0.27144 MPa/m.
Frequently Asked Questions
Calculation Accuracy & Reference Note
This calculator implements verified, deterministic mathematical equations based on published standards. Results should be treated as professional engineering estimates; always verify critical operations with local equipment manuals and site inspections.