![]() ![]() The standard material for this test is crushed California limestone which has a value of 100, meaning that it is not unusual to see CBR values of over 100 in well compacted areas. High quality crushed rock has a CBR over 80. A CBR of 3 equates to tilled farmland, a CBR of 4.75 equates to turf or moist clay, while moist sand may have a CBR of 10. ![]() The harder the surface, the higher the CBR rating. The CBR can also be used for measuring the load-bearing capacity of unimproved airstrips or for soils under paved airstrips. The CBR rating was developed for measuring the load-bearing capacity of soils used for building roads. ![]() The CBR test is fully described in BS 1377 : Soils for civil engineering purposes : Part 4, Compaction related tests, and in Part 9: In-situ tests. The CBR test is described in ASTM Standards D1883-05 (for laboratory-prepared samples) and D4429 (for soils in place in field), and AASHTO T193. The Plate Bearing Test is carried out in accordance with BS 1377 Part 9: 1990 plate bearing test code. The measured pressure is then divided by the pressure required to achieve an equal penetration on a standard crushed rock material. BS 1377 was first published in 1948 and first appeared in metric form in 1975. This test method is widely used in accordance with the British Standard. The basic site test is performed by measuring the pressure required to penetrate soil or aggregate with a plunger of standard area. It was developed by the California Department of Transportation before World War II. The California bearing ratio (CBR) is a penetration test for evaluation of the mechanical strength of natural ground, subgrades and basecourses beneath new carriageway construction. ![]()
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