CBR Test
The CBR test (California Bearing Ratio) is a path-controlled penetration test. The determined value describes the bearing capacity of a soil relative to a defined standard material (well-graded gravel of crushed California limestone) and is expressed as a percentage. It measures the force required to press a cylindrical piston with a diameter of 50 mm into a specimen at a constant velocity to a specified depth. The test is carried out in accordance with DIN EN 13286-47 and TP BF-StB Part B 7.1.
Application and Potential
CBR tests are used to determine the strength of the subgrade soil and soil-binders-mixtures in the design and construction of roads and other paved structures such as airfields, parking lots, etc. When performed on a sample that was stored in water and subjected to multiple freezing cycles, it also helps to assess the frost sensitivity of soils. Furthermore, statements can be made on the effectiveness of consolidating measures to increase the bearing capacity of soil.
Specimen Requirements
The CBR test can be performed on undisturbed or disturbed samples. For each test, a minimum of 7.5 kg of material is needed that has passed through a 22.4 mm sieve.
Technical Equipment
The modified Proctor equipment, suitable punches and several testing presses of different sensitivity and capability are available to us in our laboratory, as well as a climatic chamber to determine the CBR value after freeze-thaw cycles.
Further Information
- DIN EN 13286-47 (2012): Test method for the determination of the CBR value
- TP BF-StB Part B 7.1 (2012): Test method for the determination of the CBR values
- ZTV E-StB 17 (2017): Additional technical contract conditions for soil and rock in road construction
- Lottmann, Almut (2003): Bearing capacity and frost sensitivity of lime-treated cohesive soils in the subgrade of traffic areas. Doctoralthesis. BTU Cottbus - Senftenberg