# Resistance Value

The Resistance Value (R-value) test is a material stiffness test. The test procedure expresses a material's resistance to deformation as a function of the ratio of transmitted lateral pressure to applied vertical pressure.

- Canonical URL: https://pavementinteractive.org/reference-desk/design/design-parameters/resistance-value/
- Last updated: 2026-11-01
- Review: reviewed by licensed professional engineers on the previous Pavement Interactive site, where reviewers were not recorded by name
- Standards: AASHTO T 190, ASTM D2844

The Resistance Value (R-value) test is a material stiffness test. The test procedure expresses a material's resistance to deformation as a function of the ratio of transmitted lateral pressure to applied vertical pressure. It is essentially a modified [triaxial compression test](https://pavementinteractive.org/reference-desk/testing/aggregate-tests/triaxial-test/). Materials tested are assigned an R-value.

The R-value test was developed by F.N. Hveem and R.M. Carmany of the California Division of Highways and first reported in the late 1940's. During this time [rutting](https://pavementinteractive.org/glossary/rutting/) (or [shoving](https://pavementinteractive.org/glossary/shoving/)) in the wheel tracks was a primary concern and the R-value test was developed as an improvement on the [CBR](https://pavementinteractive.org/glossary/cbr/) test. Presently, the R-value is used mostly by State Highway Agencies (SHAs) on the west coast of the U.S.

The test procedure to determine R-value requires that the laboratory prepared samples are fabricated to a moisture and density condition representative of the worst possible in situ condition of a compacted subgrade. The R-value is calculated from the ratio of the applied vertical pressure to the developed lateral pressure and is essentially a measure of the material's resistance to plastic flow. The testing apparatus used in the R-value test is called a stabilometer (identical to the one used in [Hveem HMA mix design](https://pavementinteractive.org/reference-desk/design/mix-design/hveem-mix-design/)) and is represented schematically in Figure 1.

![R-Value Stabilometer](https://pavementinteractive.org/wp-content/uploads/2009/06/Stabilometer.jpg)

*Figure 1.* R-Value Stabilometer

Values obtained from the stabilometer are inserted into the following equation to obtain an R-value:

$$R = 100 - \left\{ \frac{100}{\left( \dfrac{2.5}{D} \right) \left[ \left( \dfrac{\mathit{Pv}}{\mathit{Ph}} \right) - 1 \right] + 1} \right\}$$

where:

- $$R$$ = resistance value
- $$\mathit{Pv}$$ = applied vertical pressure (160 psi)
- $$\mathit{Ph}$$ = transmitted horizontal pressure at Pv = 160 psi
- $$D$$ = displacement of stabilometer fluid necessary to increase horizontal pressure from 5 to 100 psi.

Some typical R-values are:

- Well-graded (dense [gradation](https://pavementinteractive.org/glossary/gradation/)) crushed stone [base course](https://pavementinteractive.org/glossary/base-course/): 80+
- MH silts: 15-30

## Standard Test Methods

- AASHTO T 190 and ASTM D 2844: Resistance R-Value and Expansion Pressure of Compacted Soils