👉CBR Definition
💫The CBR is a measure of soil strength, used to determine how thick pavement layers should be.
🏷Stronger soils (higher CBR) require thinner pavements, while weaker soils (lower CBR) need thicker pavements.
🚧Pavement Layers
1. Asphalt (surface layer) – 100 mm
2. Base (gravel/aggregates) – 150 mm
3. Sub-base (compacted coarse sand) – 200 mm
4. Compacted subgrade (natural soil foundation)
📎Steps in Design
1. Determine CBR value of subgrade soil.
- Poor: 2–4%
- Average: 4–7%
- Good: 7–10%
2. Use design charts or formulas to select thickness.
3. Adjust for traffic load and material properties.
🪧Example Calculation
- Given: CBR = 5%
- From design chart: Recommended pavement thickness = 550 mm
- This includes all layers combined.
🔖Key Notes
- Higher CBR → thinner pavement.
- Lower CBR → thicker pavement.
@etconp
💫The CBR is a measure of soil strength, used to determine how thick pavement layers should be.
🏷Stronger soils (higher CBR) require thinner pavements, while weaker soils (lower CBR) need thicker pavements.
🚧Pavement Layers
1. Asphalt (surface layer) – 100 mm
2. Base (gravel/aggregates) – 150 mm
3. Sub-base (compacted coarse sand) – 200 mm
4. Compacted subgrade (natural soil foundation)
📎Steps in Design
1. Determine CBR value of subgrade soil.
- Poor: 2–4%
- Average: 4–7%
- Good: 7–10%
2. Use design charts or formulas to select thickness.
3. Adjust for traffic load and material properties.
🪧Example Calculation
- Given: CBR = 5%
- From design chart: Recommended pavement thickness = 550 mm
- This includes all layers combined.
🔖Key Notes
- Higher CBR → thinner pavement.
- Lower CBR → thicker pavement.
@etconp
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