The CBR Test is a critical laboratory evaluation that determines soil strength after complete saturation. By simulating the adverse moisture conditions found during monsoons or in water-prone areas, it provides the "worst-case" resistance parameters essential for durable infrastructure design.
Test Objectives
- Measure mechanical strength under 96-hour saturation
- Establish design parameters for flood-prone road subgrades
- Evaluate soil expansion and swelling characteristics
Engineering Application
- Assists in pavement thickness design for high-moisture zones
- Evaluates soil performance beneath foundations in wet environments
- Validates the necessity of soil stabilization or geotextile layers
Durability & Safety
- Prevents pavement failure caused by reduced strength in wet cycles
- Ensures long-term structural safety against subgrade softening
- Aids in determining the feasibility of local soils for construction
Calculated Values
- CBR percentage at 2.5mm and 5.0mm penetration
- Measurement of Free Swell percentage during soaking
- Relationship between dry density and soaked resistance
The procedure involves compacting the soil at its Optimum Moisture Content (OMC) and then immersing the mold in water for a standard period—typically 96 hours. During this time, surcharge weights are applied to simulate the weight of the pavement layers above.
By measuring the penetration resistance after this soaking period, we identify how much the soil's load-bearing capacity degrades when exposed to groundwater or heavy rain. This data is crucial for IRC/AASHTO based pavement design, ensuring that highways do not buckle or fail during rainy seasons.
Our Laboratory Procedure
- 1 Preparation of soil samples at MDD/OMC specifications
- 2 96-hour immersion under controlled surcharge loading
- 3 High-precision penetration testing via digital CBR apparatus
- 4 Detailed reporting with soaked strength and swelling data