Bearing Tests

The bearing capacity of a soil is expressed in terms of shear resistance, which means the capacity of the load-bearing portion of a material or member to resist displacement in the direction of the force exerted by the load.

There are various types of load-bearing tests. For description purposes we will briefly discuss the California bearing ratio (CBR) test. The California bearing ratio is a measure of the shearing resistance of a soil under carefully controlled conditions of density and moisture. The CBR is determined by a penetration shear test and is used with empirical curves for designing flexible pavements.

The test procedure used to determine the CBR consists of two principal steps. First, the soil test specimens are prepared; second, a penetration test is performed upon the prepared soil samples. Although one standardized procedure has been established for the penetration portion of the test, it is not possible to establish one procedure for the preparation of test specimens since soil conditions and construction methods vary widely. The soil test specimens are prepared to duplicate the soil conditions existing, or expected to occur later, in the field. Although penetration tests are most frequently performed on laboratory-compacted test specimens, they may also be performed upon undisturbed soil samples or in the field upon the soil in place. Detailed procedures for preparing the test samples and performing the test can be found in NAVFAC MO-330.