How to Design Flexible Pavements as per IRC SP 62: Step-by-Step Guide

Designing flexible pavements is a critical process to ensure long-lasting, safe, and cost-effective road infrastructure. The Indian Roads Congress (IRC) provides detailed guidelines for pavement design through IRC SP 62 – Guidelines for the Design and Construction of Flexible Pavements for Low Volume Rural Roads.

In this blog, we will provide a step-by-step guide to designing bituminous flexible pavements in India, based on IRC SP 62 and IRC 37, focusing on road asset management in India and best practices for pavement design.

1. Understanding Flexible Pavements

Flexible pavements consist of layers of granular material and bituminous surfacing that distribute the traffic load to the subgrade. Unlike rigid pavements, flexible pavements have a gradual load distribution and can adjust to minor settlements without major cracking.

Key Components:

• Subgrade: Prepared natural soil layer.
• Sub-base: Provides additional support and drainage.
• Base Course: High-strength granular layer.
• Bituminous Surfacing: The top layer that provides a smooth, durable riding surface.

Proper design ensures reduced maintenance costs, longer pavement life, and improved road safety.

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2. Design Principles as per IRC SP 62

The IRC SP 62 design method follows a mechanistic-empirical approach, combining:

• Traffic loading analysis (cumulative million standard axles – msa).
• Soil strength evaluation using CBR (California Bearing Ratio).
• Climatic conditions and drainage provisions.

This design ensures that bituminous roads in rural and low-volume areas can handle projected traffic without premature failure.

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3. Pavement Design Steps as per IRC SP 62

Step 1 – Traffic Data Collection

Traffic data is collected through traffic surveys (RoadVision AI Traffic Survey) to estimate:

• Current and forecasted traffic.
• Number of commercial vehicles per day (CVPD).
• Design period (typically 10–15 years).

Traffic loading is converted into cumulative msa using vehicle damage factors and lane distribution.

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Step 2 – Soil Subgrade Evaluation

Soil strength is tested using the CBR method:

• At least three test pits per km are recommended.
• Soaked CBR value is used for conservative design.
• Minimum CBR for rural roads should be ≥2%.

(RoadVision AI Pavement Condition Survey helps in collecting accurate ground data.)

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Step 3 – Selection of Design Chart (IRC SP 62)

Based on:

• Traffic loading (msa).
• CBR value of subgrade.

IRC SP 62 provides design thickness charts for granular layers and bituminous surfacing.

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Step 4 – Determination of Pavement Thickness

The total pavement thickness is decided by:

• Granular Sub-base (GSB).
• Water Bound Macadam (WBM) or Wet Mix Macadam (WMM) Base.
• Bituminous surfacing (20–50 mm) depending on traffic.

For example:

• CBR 5% & 1 msa traffic:
  150 mm GSB + 150 mm WBM + 20 mm premix carpet + seal coat.

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Step 5 – Drainage and Cross-Slope Design

Proper side drains and camber (2–3%) are essential to prevent water stagnation, which is a common cause of premature pavement failure.

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Step 6 – Material Selection

• Granular materials: Well-graded, free from clay lumps.
• Bitumen: VG-10 or VG-30 for rural low-volume roads.
• Surface dressing or premix carpet for wearing course.

All materials must conform to IRC & MORTH specifications.

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Step 7 – Quality Control and Construction

• Layer-by-layer compaction testing.
• Thickness checks using templates.
• Proper prime and tack coat application between layers.

(RoadVision AI Road Safety Audit ensures that construction quality meets safety standards.)

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4. Road Asset Management and Pavement Maintenance

Even after proper design, road asset management in India is crucial.
Using AI-powered road inspection tools ensures:

• Timely detection of surface distress (potholes, cracks, rutting).
• Planning preventive maintenance to extend pavement life.
• Cost-effective road network management.

5. Importance of Following IRC SP 62

Following the IRC SP 62 design method:

• Ensures standardized, safe, and durable pavements.
• Optimizes construction costs for rural roads.
• Reduces frequent repairs, improving connectivity and safety.

For large-scale projects, AI-based pavement data collection helps improve design accuracy and long-term performance.

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Conclusion

Designing flexible pavements as per IRC SP 62 is vital for building durable, cost-effective, and safe rural roads in India. The step-by-step method, starting from traffic and soil analysis to pavement thickness design, ensures a scientific approach to road construction.

RoadVision AI is revolutionizing road infrastructure development and maintenance by leveraging cutting-edge AI in road safety and computer vision technology. Through advanced digital twin technology, the platform performs comprehensive road safety audits, enabling early detection of potholes, cracks, and other surface issues, ensuring timely repairs and improved road conditions. It also enhances traffic surveys by providing data-driven insights to address challenges like traffic congestion and optimize road usage. With a focus on building smart roads, RoadVision AI ensures full compliance with IRC Codes, empowering engineers and stakeholders to reduce costs, minimize risks, and improve the overall road safety and transportation experience.

By integrating AI-based data collection and road asset management tools, engineers can further enhance pavement design accuracy and reduce life-cycle costs.

Book a demo with RoadVision AI to learn how our AI-powered road inspection solutions can help you plan, design, and maintain pavements efficiently.

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FAQs

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Q1. What is IRC SP 62 used for?

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It provides official guidelines for designing low-volume flexible pavements in India, focusing on cost-effective and durable rural roads.

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Q2. How is traffic loading calculated in pavement design?

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Traffic surveys estimate commercial vehicles per day, which is converted into cumulative msa for design.

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Q3. Why is CBR important in pavement design?

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The CBR value defines soil strength, which determines the required pavement thickness for long-lasting roads.

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