The California Bearing Ratio (CBR) Test is one of the most widely used field and laboratory tests to evaluate the strength of subgrade soil and its suitability for road and pavement construction. It provides crucial input data for designing the thickness and layers of flexible pavements, ensuring long-term durability and performance.

The test measures the resistance of soil to penetration by a standard plunger (usually 50 mm diameter) under standard load conditions. The results are expressed as a percentage relative to a standard crushed stone sample.

Types of CBR Tests

1. Field CBR Test

Conducted directly on-site using a loading machine
Measures soil resistance under natural ground conditions
Useful for real-time assessment of subgrade soil at project locations

2. Laboratory CBR Test

Performed on compacted soil samples under controlled conditions
Analyzes soil behavior at different moisture contents and densities
Ensures reliable input data for pavement design and soil evaluation

Applications of the CBR Test

Design of flexible and rigid pavements.
Assessment of subgrade soil, sub-base, and base course materials.
Evaluation of soil stabilization techniques.
Determination of pavement thickness for highways, airfields, and industrial floors.
Quality control of construction materials on site.