The R-Value test, California Test 301, measures the response of a compacted sample of soil

Soil

Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...

 or aggregate

Construction Aggregate

Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined material in the world...

 to a vertically applied pressure under specific conditions. This test is used by Caltrans

California Department of Transportation

The California Department of Transportation is a government department in the U.S. state of California. Its mission is to improve mobility across the state. It manages the state highway system and is actively involved with public transportation systems throughout the state...

 for pavement

Pavement (material)

Road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past cobblestones and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete. Such...

 design, replacing the California bearing ratio

California Bearing Ratio

The California bearing ratio is a penetration test for evaluation of the mechanical strength of road subgrades and basecourses. It was developed by the California Department of Transportation before World War II....

 test. Many other agencies have adopted the California pavement design method, and specify R-Value testing for subgrade soils and road aggregates.

The test method states:

The R-value of a material is determined when the material is in a state of saturation such that water will be exuded from the compacted test specimen when a 16.8 kN load (2.07 MPa) is applied. Since it is not always possible to prepare a test specimen that will exude water at the specified load, it is necessary to test a series of specimens prepared at different moisture contents.

R-Value is used in pavement design, with the thickness of each layer dependent on the R-value of the layer below and the expected level of traffic

Traffic

Traffic on roads may consist of pedestrians, ridden or herded animals, vehicles, streetcars and other conveyances, either singly or together, while using the public way for purposes of travel...

loading, expressed as a Traffic Index. Details of the pavement design procedure are given in Chapter 600 of the California Highway Design Manual.