The Field California Bearing Ratio (CBR) Test is an in-situ penetration test used to evaluate the mechanical strength of subgrade soil. It measures the soil's resistance to a standardized plunger, providing the primary data required for flexible pavement design.
Test Objectives
- Measure the shear strength of subgrade soil layers
- Calculate specific CBR percentages for road thickness
- Determine soil suitability for airfield and highway sub-bases
Engineering Application
- Determines the required thickness of various pavement layers
- Supports load distribution analysis for shallow footings
- Aids in selecting effective soil stabilization techniques
Structural Importance
- Ensures long-term durability of transportation infrastructure
- Reduces the risk of premature road failure and rutting
- Provides actionable data for logistical construction planning
Safety Indicators
- Identifies weak subgrade materials early in the project
- Verifies the quality of compacted fill materials
- Standardized data for compliance with local road authorities
The Field CBR value is calculated by comparing the pressure required to penetrate the soil with a standard plunger against the pressure required for a standard high-quality crushed stone.
$$CBR = \left( \frac{p}{p_s} \right) \times 100$$
Unlike laboratory CBR, field testing accounts for the natural moisture content and actual in-situ density, ensuring that the pavement design is reflective of real environmental conditions.
Our Field CBR Methodology
- 1 Surface preparation and leveling of the subgrade layer
- 2 Incremental load application using hydraulic jacking
- 3 Real-time monitoring of resistance and penetration rates
- 4 Comprehensive reporting with pavement layer recommendations