⚙️ Flexible Pavement Input Parameters (IRC:37-2018)
📋 Design catalogue is based on IRC:37-2018 Appendix-5. Traffic computed using mechanistic-empirical approach. VDF and growth rate as per IRC:9-2020.
Commercial vehicles per day in design lane at opening
Soaked CBR of compacted subgrade (2–15%)
📊 Flexible Pavement Design Report (IRC:37-2018)
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Design Traffic (MSA)
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Total Pavement Thickness
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Subgrade CBR
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Est. Cost / km / Lane (₹ Lakh)
📐 Step-by-Step Design Calculations
📋 Pavement Layer Thickness (IRC:37-2018 Catalogue)
| # | Layer | Material | Thickness (mm) | Compaction | Remarks |
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🖼️ Pavement Cross-Section Diagram
📦 Material Quantities per km per Lane
| Layer | Width (m) | Thickness (m) | Volume (m³/km) | Density (T/m³) | Quantity (T/km) |
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💰 Cost Estimate per km per Lane
| Layer | Quantity | Rate | Amount (₹) |
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📊 Pavement Layer Thickness Chart
⚙️ Rigid Pavement Input Parameters (IRC:58-2015)
📋 Design is based on IRC:58-2015 (PQC slab design). Edge stress and fatigue analysis as per Annexure A. k-value from IRC:SP:72.
Commercial vehicles per day (both directions)
Soaked CBR; k-value auto-calculated
Leave blank to auto-calculate from CBR
📊 Rigid Pavement Design Report (IRC:58-2015)
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Design Traffic (×10⁶ axles)
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Slab Thickness (mm)
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Radius of Relative Stiffness (m)
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Est. Cost / km / Lane (₹ Lakh)
📐 Step-by-Step Design Calculations (IRC:58-2015)
📋 Pavement Structure
| # | Layer | Material | Thickness (mm) | Specification |
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🖼️ Pavement Cross-Section Diagram
🔩 Joint Details
| Joint Type | Spacing | Depth | Filler | Bar Details |
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🔧 Reinforcement / Bar Details
| Bar Type | Diameter (mm) | Length (mm) | Spacing (mm) | Zone |
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📦 Material Quantities per km per Lane
| Item | Width (m) | Thickness (m) | Volume (m³/km) | Quantity |
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💰 Cost Estimate per km per Lane
| Item | Quantity | Rate | Amount (₹) |
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📊 Rigid Pavement Structure Chart
Pavement Design in India — IRC Standards
IRC:37-2018 — Flexible Pavement
The IRC:37-2018 guideline adopts a mechanistic-empirical approach for flexible pavement design. The design traffic is expressed in cumulative standard axle load repetitions (CSAR or MSA). The pavement thickness catalogue is based on subgrade CBR and design MSA, covering traffic from 1 MSA to 300 MSA and CBR from 2% to 10%.
- Granular Sub-base (GSB) — filter + drainage layer
- Wet Mix Macadam (WMM) — base course
- Dense Bituminous Macadam (DBM) — binder course
- Bituminous Concrete (BC) — wearing course
IRC:58-2015 — Rigid Pavement
IRC:58-2015 uses fatigue and erosion analysis for Pavement Quality Concrete (PQC) slab design. The modulus of subgrade reaction (k) is determined from CBR and sub-base type. The radius of relative stiffness (l) is the key parameter governing load distribution in the concrete slab.
- Dry Lean Concrete (DLC) sub-base for stiff support
- PQC slab thickness from 200mm to 350mm
- Contraction joints @ 4.5 m spacing (typical)
- Expansion joints @ 140–180 m intervals
FAQs
Frequently Asked Questions
What is MSA in flexible pavement design?
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MSA stands for Million Standard Axles. It is the design traffic expressed as the cumulative number of standard axle load (80 kN single axle) repetitions that the pavement will carry during its design life. It accounts for traffic volume, vehicle damage factor (VDF), lane distribution, traffic growth rate and design period. IRC:37-2018 provides pavement thickness catalogues for 1, 2, 5, 10, 20, 30, 50, 100, 150, 200, 300 and 500 MSA.
What is the difference between flexible and rigid pavement?
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Flexible Pavement: Uses bituminous (asphalt) layers over granular base and sub-base. Distributes load through grain-to-grain contact. Deflects under load. Designed as per IRC:37-2018. Initial cost is lower but requires periodic overlay every 5–7 years.
Rigid Pavement: Uses Portland Cement Concrete (PCC) slab that acts as a beam and distributes load over a larger area. Less deflection. Designed as per IRC:58-2015. Higher initial cost but lasts 30–40 years with minimal maintenance. Preferred for high-traffic highways, port roads and urban intersections.
Rigid Pavement: Uses Portland Cement Concrete (PCC) slab that acts as a beam and distributes load over a larger area. Less deflection. Designed as per IRC:58-2015. Higher initial cost but lasts 30–40 years with minimal maintenance. Preferred for high-traffic highways, port roads and urban intersections.
What CBR value should be used for pavement design?
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The soaked CBR of the compacted subgrade should be used for design. IRC:37-2018 recommends testing at 97% modified Proctor compaction and 4-day soaking. The design CBR should be the 80th percentile value (i.e., 80% of test results exceed this value) when multiple samples are tested. Typical CBR values: Black cotton soil 2–4%, sandy soil 5–10%, gravel 10–15%. Using soaked CBR ensures the worst-case (post-monsoon) condition is designed for.
What is the radius of relative stiffness in rigid pavement?
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The radius of relative stiffness (l) is a fundamental parameter in rigid pavement design that represents the distance over which the concrete slab distributes a concentrated load. It is calculated as:
where E = elastic modulus of concrete (~5000√fck MPa), h = slab thickness (m), μ = Poisson's ratio (0.15 for concrete), and k = modulus of subgrade reaction (MPa/m). A larger l value means the slab is stiffer relative to the subgrade, resulting in better load distribution.
l = [E×h³ / (12×(1-μ²)×k)]^0.25where E = elastic modulus of concrete (~5000√fck MPa), h = slab thickness (m), μ = Poisson's ratio (0.15 for concrete), and k = modulus of subgrade reaction (MPa/m). A larger l value means the slab is stiffer relative to the subgrade, resulting in better load distribution.
What is the purpose of dowel bars in concrete pavement joints?
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Dowel bars are smooth, round mild steel bars placed across transverse contraction joints in concrete pavement. Their purposes are: (1) Transfer load across the joint so that one slab helps support the adjacent slab under wheel loads — preventing differential deflection, (2) Prevent relative vertical movement (faulting) at the joint. Per IRC:58-2015, dowel bars are 32–38 mm diameter, 500 mm long, placed at mid-slab depth, spaced at 300 mm c/c. One end is bonded to concrete; the other end is de-bonded (greased/sleeved) to allow horizontal movement during thermal expansion/contraction.