1. California Bearing Ratio
Prepared by
Arunangsu Patra
Under the Guidance of
Prof. Jayashree Sengupta
Department of Civil Engineering
Sir J. C. Bose School of Engineering
Supreme Knowledge Foundation Group of Institutions

2. INTRODUCTION:
The behavior of road surface depends on the strength of the fill material and the subgrade below it. This strength of the subgrade soil is expressed as California Bearing Ratio (CBR)
It was developed by California State Highway Department (USA) for evaluating the bearing capacity of subgrade soil for design of flexible pavement, before second world war.
It is the ratio of test load to the standard load at a specified penetration by a standard plunger under controlled density and moisture conditions.

3. How the test is done:
The test is performed by measuring the pressure required to penetrate a soil sample with a plunger of standard area.
The measured pressure is then divided by the pressure required to achieve an equal penetration on a standard crushed rock material.
And using the values obtained from the test from an empirical design chart, the pavement thickness are calculated.

4. classification:
Laboratory Test
Field Test

5. CBR LABORATORY TEST Specimen may be Mould Prepared In-situ
150mm diameter
127.3mm height
Separate base plate
A collar

6. APPARATUS USED:
MOULD with COLLAR
SPACER DISC
&
WEIGHTS
RAMMERS

7. APPARATUS USED: (Contd.)
WHOLE APPARATUS
LOADING MACHINE

8. CBR Laboratory TEST SET-UP
Proving Ring
Dial Gauge To Measure Load
Plunger 50mm DIA
Dial Gauge To Measure Penetration
Surcharge Weight, 147mm DIA
Soil Sample
Inner DIA of Mould, 150mm
Base Plate

9. laboratory CBR TEST: procedure
The specimen is soaked and the expansion is measured.
Load is applied by the loading frame through a cylinder plunger of 50mm diameter and penetration is measured.
Rate of penetration is maintained at 1.25mm/minute.
Loads are recorded for 2.5 and 5.0mm.
Load is expressed as a percentage of the standard load at the respective deformation level, and is known as the CBR value.

10. laboratory CBR TEST: procedure
Load a piston at a constant rate
See what load it takes to make it penetrate a known amount

11. CBR Equation x =
material resistance or the unit load on the piston (pressure) for 2.5 mm or 5 mm of penetration y
standard unit load (pressure) for well graded crushed stone.
For 2.5 mm of penetration = 1370 kg
For 5.0 mm of penetration = kg

12. CBR GRAPH

13. TYPICAL CBR VALUES Description of Material CBR
Well-graded crushed aggregates
100
Well-graded natural gravels 80
Silty gravel or silty, sandy gravel
40-80
Well-graded sands, gravelly sands
20-50
Clayey gravel or sandy, clayey gravel
20-40
Silty or clayey sands
10-40
Fine clean sands
10-20
Lean (low-plasticity) clays, sandy clays
5-15
Silts, sandy silts
Organic silts, lean organic clays
4-8
Fat (high-plasticity) clays
3-5

14. FIELD CBR TEST

15. FIELD CBR TEST: procedure

16. SCOPE FOR FUTURE WORK
To incorporate stabilizers like cement, fly ash, rice husk ash, etc and
To experimentally investigate the CBR improvement by using the above materials as stabilizers.

17. Thank You