The California Bearing Ratio (CBR) test is used to determine the bearing capacity of soil subgrades and base course materials. The test involves measuring the penetration of a piston into a remolded soil sample under increasing loads. Loads are applied to penetrate the soil at 1.25 mm/min up to 12.5 mm. The CBR value is calculated by dividing the load measured from the soil sample at a given penetration by the standard load value for that penetration from a reference material with a CBR of 100%. Higher CBR values indicate soils with greater bearing capacity for supporting structures.

1. Topic:-
CALIFORNIA BEARING RATIO TEST
(cbr test)
SUMBITTED BY:-
UJASH B. PATEL
CIVIL-2
ER NO:-156290306544
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2. The CBR apparatus consists of:-
1.Mould :-150mm diameter & 175 height
2.Plunger:-50mm dia meter
3.Base plate
4.Collar
5.Loading frame
6.Proving ring
7.Dial gauges
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4.  Calculate the CBR value using following formula.
Corrected Load Value
CBR% - x 100
Standard Load
PENETRATION(MM) TOTAL STANDARD LOAD (K
D UNIT STANDARD LOAD (k cm2)
2.5 1370 70
5.0 2055 105
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5.  STANDARD
IS: 2720 (Part 16) 1979.
DEFINITION
California bearing ratio is the ratio of force per unit area required to penetrate in
to a soil mass with a circular plunger of 50mm diameter at the rate of 1.25mm /
min.
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6. Penetration of plunger (mm) Standard load (kg)
2.5
5.0
7.5
10.0
12.5
1370
2055
2630
3180
3600
 It is the ratio of force per unit area required to penetrate a soil mass with standard circular
piston at the rate of 1.25 mm/min. to that required for the corresponding penetration of a
standard material.
 C.B.R. ={ Test load/Standard load } 100%
 The following table gives the standard loads adopted for different penetrations for the
standard material with a C.B.R. value of 100.
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7. REMOULDED SPECIMEN:-
 Prepare the remoulded specimen at Proctors maximum dry density or any other
at which C.B.R is required.
 Maintain the specimen at optimum moisture content or the field moisture as required.
 The material used should pass 20 mm I.S. sieve but it should be retained on 4.75 mm
sieve. Prepare the specimen either by dynamic compaction or by static compaction.
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8.  PENETRATION TEST:-
 Place the mould assembly with the surcharge weights on the penetration
test machine.
 Seat the penetration piston at the center of the specimen with the smallest
possible load, but in no case in excess of 4 kg so that full contact of the
piston on the sample is established.
 Set the stress and strain dial gauge to read zero. Apply the load on the
piston so that the penetration rate is about 1.25 mm/min.
 Record the load readings at penetrations of 0.5, 1 .0, 1.5, 2.0, 2.5, 3.0, 4.0,
5.0, 7.5, 10 and 12.5 mm.
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9.  CORRESPONDING TO THE PENETRATION VALUE AT
WHICH CBR IS TO BE DESIRED, TAKE THE CORRECTED
LOAD VALUES FROM THE LOAD PENETRATION CURVE
AND CALCULATE THE CBR FROM THE EQUATION
PT X CF
 CALIFORNIA BEARING RATIO = ------------- X 100.
 PS
 PT =CORRECTED UNIT TEST LOAD CORRESPONDING
TO THE CHOSEN PENETRATION FROM LOAD
PENETRATION CURVE
 PS = TOTAL STANDARD LOAD FOR THE SAME DEPTH
OF PENETRATION, WHICH CAN BE TAKEN FROM THE
TABLE BELOW
 CF = PROVING RING CORRECTION FACTOR.
 LOAC-PENETRATION ON CURVE:-
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10. Thank you
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