ASTM D1883, AASHTO R74 Soil CBR Tester, California Bearing Ratio test, 

Soil preparation: the soil sample is compacted to a specific density and moisture content using a standard Proctor compaction test.

CBR determination: a cylindrical mold containing the compacted soil is placed under a load-testing machine. A standard penetrometer is then forced into the soil at a controlled rate. The load required to achieve a penetration of 0.5 inches (12.7 mm) is recorded.

CBR calculation: the CBR is calculated as the ratio of the load required to achieve 0.5 inches of penetration in the test soil to the load required to achieve the same penetration in a standard aggregate base material.

The California Bearing Ratio (CBR) is a test method proposed by the state of California in the United States to assess the bearing capacity of subgrade materials. The bearing capacity is characterized by the material's ability to resist deformation caused by localized loading, expressed as a percentage relative to the bearing capacity of standard crushed stone, referred to as the CBR value. This method has also been used to assess the strength of soil foundations, defined as the ratio of the test load applied at an 2.5 mm penetration to the load applied by standard crushed stone material at the same penetration, expressed as a percentage. Due to the simplicity of the CBR testing method and its low equipment costs, it has been widely used in many countries. The CBR method is used to determine the thickness of asphalt pavements, with accompanying charts making it highly convenient, and it is well received by engineering professionals.

UT4065A Soil CBR tester used to conduct load ratio tests on various soils and pavement base and sub-base materials after making specimens in the specified test tube. The maximum particle size of the mixture should be controlled within 25mm, with a maximum of no more than 40mm.

Main standard: 

ASTM D1883 – Standard Test Method for California Bearing Ratio (CBR) of Laboratory-Compacted Soils

AASHTO R74 – Standard Practice for Wet Preparation of Disturbed Soil Samples for Test.

Operation: 

1. Turn on the power switch, operate the instrument, check if the working condition of the instrument is normal, check if the handle is in and out, and if the rotation is normal. If everything is normal, prepare to start the test.

2. Prepare specimens according to the bearing ratio test method specified in JTJ075-85 "Test Code for Highway Pavement Base Materials".

3. Measurement of water swelling:

A、 Place the moisture cured specimen on a porous plate equipped with an adjusting rod, and apply sufficient load plate on the plate to ensure that the pressure on the specimen surface is equal to the pressure on the road surface of the material layer,

B、 Place the test tube and porous plate together in the water tank (without draining water first) and tighten the mold with a pull rod. Install a dial gauge and read the initial reading.

C、 Pour water into the sink to allow it to freely enter the top of the specimen. During the saturation period, the water in the sink should be kept 25mm above the top surface of the specimen. Typically, the specimen needs to be soaked for 96 hours,

D、 When the soaking time is up, read the dial gauge and calculate the expansion amount.

AV=change in specimen height after immersion in water/original specimen height (120mm) x 100%

E、 Take out the sample from the sink, pour out the water on the sample, let it stand for 15 minutes to drain, then remove the additional load, porous plate, bottom plate, and filter paper, and bear the weight M to calculate the depth and density changes of the sample.

4. Penetration test:

A、 Place the saturated water test specimen on the lifting plate of the testing instrument, adjust the alignment between the penetration rod and the force measuring ring, and place a predetermined number of load plates around the penetration rod.

B、 First, apply a 45N load to the penetration rod with the handwheel, and then adjust the force measuring ring and the dial gauge for measuring deformation to zero.

C、 Load and press the handwheel,

Bearing ratio C=unit pressure/7 or 10.5 × 100%

ASTM D1883 – Standard Test Method for California Bearing Ratio (CBR) of Laboratory-Compacted Soils

AASHTO R74 – Standard Practice for Wet Preparation of Disturbed Soil Samples for Test.