Significance and Use
Field in-place CBR tests are used for evaluation and design of flexible pavement components such as base and subbase course and subgrades and for other applications (such as unsurfaced roads) for which CBR is the desired strength parameter. If the field CBR is to be used directly for evaluation or design without consideration for variation due to change in water content, the test should be conducted under one of the following conditions: (a) when the degree of saturation (percentage of voids filled with water) is 80 % or greater, ( b) when the material is coarse grained and cohesionless so that it is not significantly affected by changes in water content, or ( c) when the soil has not been modified by construction activities during the two years preceding the test. In the last-named case, the water content does not actually become constant, but generally fluctuates within a rather narrow range. Therefore, the field in-place test data may be used to satisfactorily indicate the average load-carrying capacity.
Any construction activities, such as grading or compacting, carried out subsequent to the bearing ratio test will probably invalidate the results of the test.
Note 1—Field in-place tests are used to determine the relative strength of soils, subbase, and some base materials in the condition at which they exist at the time of testing. Such results have direct application in test section work and in some expedient construction, military, or similar operations. Also, as indicated in 3.1, field in-place tests can be used for design under conditions of nominal stability of water, density, and general characteristics of the material tested. However, any significant treating, disturbing, handling, compaction, or water change can affect the soil strength and make the prior to test determination inapplicable, leading to the need for retest and reanalysis.
1.1 This test method covers the determination of the California Bearing Ratio (CBR) of soil tested in place by comparing the penetration load of the soil to that of a standard material. This test method covers the evaluation of the relative quality of subgrade soils, but is applicable to subbase and some base-course materials. This test method is designed to test in-situ materials and corresponds to Test Method D 1883.
1.2 The values stated in inch-pound units are to be regarded as the standard.
1.3 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.