What is the CBR Test?(California Bearing Ratio)To make it easier for everyone to understand, our company has compiled some relevant information and materials to share with you.

The California Bearing Ratio(CBR)Test is one of the most important geotechnical tests used to evaluate the bearing capacity of subgrade,sub-base,and base course materials in road and airfield pavement design.

In simple words→CBR tells us how strong the ground is and how much pavement thickness is needed.

Purpose of the CBR Test

To determine soil strength and stiffness under controlled density and moisture conditions.

To help design economical pavement thickness based on soil support value

To assess the impact of soaking conditions,especially in clayey soils

Higher CBR→stronger soil→thinner pavement

Lower CBR→weaker soil→thicker pavement

Laboratory CBR Test(ASTM D1883/AASHTO T193)

1 Sample Preparation

Soil dried,sieved,and mixed to required moisture content.

Compacted into a mold in 3 or 5 layers using

Standard(ASTM D698)or Modified(ASTM D1557)compaction energy.

Surcharge weights added to simulate pavement pressure

2 Soaking

Specimen is soaked for 4 days to simulate worst-case wet conditions.

3 Penetration

A 50 mm diameter plunger penetrates the soil at 1.25 mm/min.

Loads recorded at 0.25 mm,0.5 mm,1.0 mm,2.0 mm,etc.

The highest CBR value(usually between 2.5&5.0 mm)is reported.

Field CBR Test

Conducted directly on site.

Replicates in-situ soil behavior.

Quick evaluation of compacted layers(subgrade,sub-base,base).

Useful during quality control of road construction.

Typical CBR Values

Material CBR(%):Crushed Stone 80-100,

Well-Graded Gravel 40-80,Sandy Clay 10-20,Clayey Soil(Soft)2-5,Poor Wet Subgrade<2

Key Standards&Specifications

ASTMD1883-CBR Test for Laboratory Soil AASHTOT193-Standard Method of Test for CBR

ASTM D698/D1557-Soil Compaction Standards

BS1377 Part 4-CBR Determination

MORTH Section300-Road Work Soil Testing Requirements

AASHTO M 145-Soil Classification

ASTMD2487-Unified Soil Classification System(USCS)