CBR TEST

1. CALIFORNIA BEARING RATIO (CBR) Test of Soil
COURSE NAME: Bachelor of Technology in Civil Engineering
The subject is Pavement Materials
Paper Code: CE(PE)801D
Name of the student: ANANYA BISWAS
Roll no: 27901320049.
4th – Year; 8th - Semester
Name of Faculty: Mrs Sangita Debnath

2. Introduction
• The California Bearing Ratio devised by
engineers of the California Division of Highways
in nine years period to 1938.
• Most universally accepted pavement design
methods.
• A standard penetration-type load-deformation
test is carried out, and using the values
obtained from the test from an empirical design
chart, the pavement thickness are calculated.

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

4. CBR Equipment
Typical Testing Machine
Soaking Samples

5. CBR Equipment
CBR Test – Load-Penetration
Measurement
CBR Test – Sample Preparation

6. California Bearing Ratio (CBR)
• Load a piston at a
constant rate
• See what load it
takes to make it
penetrate a known
amount

7. CBR Equation









y
x
CBR 100
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 = 1000 psi
For 5.0 mm of penetration = 1500 psi

8. General Soil Type USC Soil Type CBR Range
Clean gravels
GW 40 – 80
GP 30 – 60
Gravels with fines
GM 20 – 60
GC 20 – 40
Clean sands
SW 20 – 40
SP 10 – 40
Sands with fines
SM 10 – 40
SC 5 – 20
Silts and clays
ML 15 or less
CL 15 or less
OL 5 or less
MH 10 or less
CH (LL>50%) 15 or less
OH 5 or less
Typical
CBR
Ranges

9. California Bearing
Ratio Equipment
California Bearing
Ratio Vs Moisture
content

10. CBR DESIGN METHOD
• In this method, the CBR values are used to
determine the total thickness of the flexible
pavement and its various layers.
• Following are the graphs used in the design of the
pavement thickness.

11. Flexible Pavement Design Using CBR
(Road Note 31)

21. Thank You…