California Bearing Ratio

The RT CBR device.California-Bearing-Ratio-Ap

With the DCP you can obtain the following results on a soil:

1) The CBR (California Bearing Ratio) of granular materials as a percentage

2) The UCS (Unconfined Compression Strength) of cemented materials for the CBR the following formula is applicable (note: calibrated for a DCP with certain specifications eg. angle of penetrating point and weight, you can perhaps compare it to your graph within your manual):

– If penetration rate (DN) > 2 mm/blow: then CBR = 410 x DN ^ (-1.27) – If penetration rate (DN) <= 2mm/blow: then CBR = (66.66 x DN ^ 2) – (330 x DN) + 563.33 CBR = percentage

To convert the CBR to UCS the following formula is applicable: UCS = 15 x CBR ^ 0.88 The UCS is measured in kPa (kilopascal) In order to compare the abovementioned bearing capacity (CBR of UCS) with the compaction of a specific soil type you can use COLTO or TRH specifications on materials (see attached) Kind regards Terence


From Wikipedia, IN 1928, OJ Porterproposed the California division of highway developed method for pavement design. The majority of design curves developed later are based on the orignel curves. The California bearing ratio (CBR) is a penetration test for evaluation of the mechanical strength of road subgrades and basecourses. The California Department of Transport Dept was implenting it before 1939.

The CBR Test

The test is performed by measuring the pressure required to penetrate a soil sample with a plunger of standard area.

The pressure measured by then divided by the pressure required to achieve an equal penetration on a standard crushed rock material. For more information about the CBR test consult the ASTM Standards D1883-05 (for laboratory-prepared samples) and D4429 (for soils in place in field), and AASHTO T193. The CBR test is fully described in BS 1377 : Soils for civil engineering purposes : Part 4,

RT Agencies’s CBR is electronic.


Compaction related tests. CBR ratings were developed for measuring the load-bearing capacity of soils used in test when roads are build. The CBR is also be used for measuring the load-bearings or for soils under paved airstrips. The if the surface is harder the, the higher the CBR rating.

A Californai Bearing Ratio 3 equates to tilled farmland,

4.75 equates to turf or moist clay,

moist sand’s CBR of 10.

High quality crushed rock has a CBR over 80.

California limestone has a value of 100.

cbr_drawing Matest


Civil Lab.pdf

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