The California bearing ratio (CBR) is a penetration test for evaluation of the mechanical strength of road subgrades and basecourses. It was developed by the California Department of Transportation.
The test is performed by measuring the pressure required to penetrate a soil sample with a plunger of standard area. The measured pressure is then divided by the pressure required to achieve an equal penetration on a standard crushed rock material. The CBR test is described in ASTM Standards D1883-05 (for laboratory-prepared samples) and D4429 (for soils in place in field), and AASHTO T193.
The CBR rating was developed for measuring the load-bearing capacity of soils used for building roads. The CBR can also be used for measuring the load-bearing capacity of unimproved airstrips or for soils under paved airstrips. The harder the surface, the higher the CBR rating. A CBR of 3 equates to tilled farmland, a CBR of 4.75 equates to turf or moist clay, while moist sand may have a CBR of 10. High quality crushed rock has a CBR over 80. The standard material for this test in Crushed California Limestone which has a value of 100.
= CBR
= measured pressure for site soils
= pressure to achieve equal penetration on standard soil
External links
- CBR
Topics in geotechnical engineering
Soils
Clay · Silt · Sand · Gravel · Peat
Soil properties
Hydraulic conductivity · Water content · Void ratio · Bulk density · Thixotropy · Reynolds’ dilatancy · Angle of repose · Cohesion · Porosity · Permeability · Specific storage
Soil mechanics
Effective stress · Pore water pressure · Shear strength · Overburden pressure · Consolidation · Soil compaction · Soil classification · Shear wave · Lateral earth pressure
Geotechnical investigation
Cone penetration test · Standard penetration test · Exploration geophysics · Monitoring well · Borehole
Laboratory tests
Atterberg limits · California bearing ratio · Direct shear test · Hydrometer · Proctor compaction test · R-value · Sieve analysis · Triaxial shear test · Hydraulic conductivity tests · Water content tests
Field tests
Crosshole sonic logging · Nuclear Densometer Test
Foundations
Bearing capacity · Shallow foundation · Deep foundation · Dynamic load testing · Wave equation analysis
Retaining walls
Mechanically stabilized earth · Soil nailing · Tieback · Gabion · Slurry wall
Slope stability
Mass wasting · Landslide
Earthquakes
Soil liquefaction · Response spectrum · Seismic hazard · Ground-structure interaction
Geosynthetics
Geotextile · Geomembranes · Geosynthetic clay liner
Instrumentation for Stability Monitoring
Deformation monitoring · Automated Deformation Monitoring
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Categories: Road transport | Pavements | Soil tests