CBR TEST Practical

Abstract: The report consist of experiment which

is performed in geotechnical laboratory. The test was

simple and its experimental and graphical results are

shown in this report.

Prepared By:

Student Number:

Module Code:

Module Tutor:

Assignment Number:

Due Date:

GEOTECHNICAL LABORATY

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TABLE OF CONTENTS

1.1 OBJECTIVE……………………………………………………………………..03

1.2 SIGNIFICANCES……………………………………………………….………03

1.3 THEORY……………………………………………………….……….……….04

1.4 CALIFORNIA BEARING RATIO……………………………………………...04

1.5 EXPERIMENTAL CALCULATIONS………………………………………….05

1.6 GRAPHICAL REPRESENTATION……………………………………………11

1.7 CONCLUSION & DECISION…………………………………………………..15

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EXPERIMENT 01:

CALIFORNIA BEARING RATIO TEST

1.1 OBJECTIVES:

The objectives of CBR Test are to obtain the strength of:

� Sub grade soil

� Sub-base course

� Base course material

For use in Road and Air Field pavements.

1.2 SIGNIFICANCE:

The CBR test is commonly used to evaluate the strength of sub grade soil, sub base, base

course materials for design of thickness of highways and air field pavements. The CBR test is also

known as penetration test which means to evaluation of sub grade strength of roads and pavements.

The results obtained by this penetration test are then used with empirical curves to obtain the thickness

of pavements and all other layers.

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1.3 THEORY:

1.4 CALIFORNIA BEARING RATIO:

CBR is defined as the ratio of force per unit area which is required to penetrate a soil mass with

the help of a piston with 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

1.4.1 CBR TEST:

California bearing ratio test or in other words it is also termed as CBR; first time was

developed by California Division of Highways in America. CBR test is a method which involves the

determination of sub base and base course material for flexible pavement design. This test is also used

to determine the material properties for pavement design. The CBR test is a penetration test, having a

standard piston with an area of 3 in2 (or 50 mm diameter). The test is performed by measuring the

pressure required to penetrate the soil sample with a plunger. The measured pressure is then divided by

pressure required to achieve an equal penetration on standard crushed rock material. The CBR is a

measure of resistance of a material to penetration of standard plunger under controlled density and

moisture conditions. The test procedure should be strictly adhered if high degree of reproducibility is

desired. The CBR test may be conducted in re-moulded or undisturbed specimen in the laboratory. The

test is simple and has been extensively investigated for field correlations of flexible pavement

thickness requirement.

The CBR test consist apparatus of a mould of 150 mm diameter with base plate and collar, dial

gauges for measuring the penetration values, spacer disc, metal rammers and sieves ranging from 4.75

mm to 20 mm.

1.4.2 TEST PROCEDURE

Following steps should be taken during this test.

� Place the mold assembly with the surcharge weights on penetration test machine.

� Set the penetration piston at the center of the sample with smallest possible load, so that

full contact of piston on sample is established.

� Set the stress and strain dial gauges to read zero. Apply the load on the piston so that the

penetration rate is about 1.25 mm/min.

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� Record the load readings at penetrations of 0.25, 0.5, 0.75, 1.00, 1.25, 1.5, 1.75, 2.00,

2.25, 2.5, 2.75, 3.00, 3.25, 3.5, 3.75, 4.00, 4.25, 4.5, 4.75, 5.00, 5.25, 5.5, 5.75, 6.00,

6.25, 6.5, 6.75, 7.00, 7.25, 7.5.

� Detach the mould from loading equipment. Take about 20 g to 50 g of soil from top 3

cm layer and determine the moisture content.

1.5 EXPERIMENTAL CALCULATION

TABLE # 01

Location Job Ref.

Borehole/Pit

no.

Soil Description Sample no. 5 ml

Depth

Test Method BS-1377-4: 1990: 7.4

Force measuring device No.

Penetration

Force

gauge Force on

Penetration Force gauge Force on

of Plunger reading plunger of Plunger reading plunger

mm div KN mm div KN

0 0 0 0 0

4.00 29 12 219.69 60

0.25 11 3 83.33 15

4.25 38 18 287.87 90

0.50 24 14 181.8 70

4.50 46 23 348.48 115

0.75 38 24 287.87 120

4.75 53 32 401.51 160

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1.00 34 33 257.57 165

5.00 60 38 454.54 190

1.25 71 41 537.87 205

5.25 67 44 507.57 220

1.50 89 47 674.24 235

5.50 73 51 553.03 255

1.75 6 54 45.45 270

5.75 79 56 598.48 280

2.00 24 61 181.8 305

6.00 85 62 643.93 310

2.25 30 68 227.27 340

6.25 92 68 696.96 340

2.50 53 74 401.5 370

6.50 98 73 742.42 365

2.75 68 81 515.15 405

6.75 4 79 30.3 395

3.00 83 87 628.78 435

7.00 10 86 75.75 430

3.25 95 93 719.69 465

7.25 16 92 121.21 460

3.50 7 99 53.03 495

7.50 21 98 159.09 490

3.75 18 5 136.36 25

Container No 1 2 CBR value at

Mass of Wet Soil + container (m2) g 250.6 265.8 penetration of:

Mass of Dry Soil + container (m3) g 247 260.2

Mass of container (m1) g 198.1 198.1

2.5

mm

5

mm

Mass of moisture (m2-m3) g 3.6 5.6 Top 30.4 34.43

Mass of Dry Soil (m3-m1) g 48.9 62.1

Moisture content 7.40% 9%

Bottom 18.5 9.5

w = ((m2-m3)/(m3-m1)) * 100

Average Moisture content % 8.20% Accepted CBR % = 34.43

Operator Checked Approved

TABLE #02

Location Job Ref.

Borehole/Pit

no.


Depth

Test Method BS-1377-4: 1990: 7.4


Penetration

Force

gauge Force on


of Plunger reading plunger


mm div KN mm div KN

0 0 0 0 0

4.00 112 91 848.48 455

0.25 1 1 7.57 5

4.25 121 96 916.66 480

0.50 2 3 15.15 15

4.50 130 101 984.84 505

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0.75 3 8 22.72 40

4.75 139 106 1053.03 530

1.00 7 14 53.03 70

5.00 146 111 1106.06 555

1.25 13 20 98.48 100

5.25 153 115 1159.09 575

1.50 19 27 143.93 135

5.50 161 120 1219.69 600

1.75 26 33 196.96 165

5.75 167 125 1265.15 625

2.00 34 40 257.57 200

6.00 174 130 1318.18 650

2.25 44 46 333.33 230

6.25 180 135 1363.63 675

2.50 52 53 393.93 265

6.50 187 139 1416.66 695

2.75 63 60 477.27 300

6.75 193 143 1462.12 715

3.00 71 67 537.87 335

7.00 197 147 1492.42 735

3.25 84 73 636.36 365

7.25 204 151 1545.45 755

3.50 94 79 712.12 395

7.50 209 155 1583.33 775

3.75 103 85 780.3 425




Mass of container (m1) g 198.2 210.4 2.5 mm

5

mm



Moisture content 11.90% 11.4%

Bottom 20 27.75

w = ((m2-m3)/(m3-m1)) * 100



TABLE # 03

Location Job Ref.

Borehole/Pit

no.


Depth

Test Method BS-1377-4: 1990: 7.4


Penetration

Force

gauge Force on




mm div KN mm div KN

0 0 0 0 0

4.00 66 60 500 300

0.25 1 2 7.57 10

4.25 70 63 530.3 315

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0.50 2 7 15.15 35

4.50 75 69 568.18 345

0.75 3 9 22.72 45

4.75 79 73 598.48 365

1.00 5 12 37.87 60

5.00 82 77 621.21 385

1.25 9 14 68.18 70

5.25 88 80 666.66 400

1.50 13 17 98.48 85

5.50 92 84 696.96 420

1.75 18 21 136.36 105

5.75 95 87 719.69 435

2.00 24 25 181.81 125

6.00 99 91 750 455

2.25 29 28 219.69 140

6.25 102 94 772.72 470

2.50 33 32 250 160

6.50 106 96 803.03 480

2.75 41 37 310.6 185

6.75 109 100 825.75 500

3.00 46 42 348.48 210

7.00 113 103 856.06 515

3.25 51 47 386.36 235

7.25 116 107 878.78 535

3.50 56 51 424.24 255

7.50 120 108 909.09 540

3.75 61 55 462.12 275





2.5

mm

5

mm




Bottom 8 19.25

w = ((m2-m3)/(m3-m1)) * 100



TABLE # 04

Location Job Ref.

Borehole/Pit

no.


Depth

Test Method BS-1377-4: 1990: 7.4


Penetration

Force

gauge Force on




mm div KN mm div KN

0 0 0 0 0

4.00 141 121 1068.18 605

Page | 9

0.25 12 20 90.9 100

4.25 145 126 1098.48 630

0.50 24 33 181.81 165

4.50 150 130 1136.36 650

0.75 36 42 272.72 210

4.75 154 134 1166.66 670

1.00 50 51 378.78 255

5.00 158 139 1196.96 695

1.25 64 59 484.84 295

5.25 163 143 1234.84 715

1.50 75 66 568.18 330

5.50 168 148 1272.72 740

1.75 84 72 636.36 360

5.75 171 152 1295.45 760

2.00 92 78 696.96 390

6.00 176 157 1333.33 785

2.25 99 82 750 410

6.25 180 161 1363.63 805

2.50 106 90 803.03 450

6.50 185 166 1401.51 830

2.75 113 95 856.06 475

6.75 189 170 1431.81 850

3.00 119 100 901.51 500

7.00 193 175 1462.12 875

3.25 125 106 946.96 530

7.25 197 179 1492.42 895

3.50 130 111 984.84 555

7.50 202 184 1530.3 920

3.75 134 116 1015.15 580


Mass of Wet Soil + container (m2) g 280 295.4 penetration of:

Mass of Dry Soil + container (m3) g 273.8 287.9


2.5 mm 5

mm




Bottom 22.5 34.75

w = ((m2-m3)/(m3-m1)) * 100



TABLE # 05

Location Job Ref.

Borehole/Pit

no.


Depth

Test Method BS-1377-4: 1990: 7.4


Penetration

Force

gauge Force on




mm div KN mm div KN

Page | 10

0 0 0 0 0

4.00 103 123 780.3 615

0.25 15 24 113.63 120

4.25 107 127 810.6 635

0.50 26 42 196.96 210

4.50 111 132 840.9 660

0.75 36 53 272.72 265

4.75 115 135 871.21 675

1.00 45 61 340.9 305

5.00 119 139 901.51 695

1.25 53 67 401.51 335

5.25 123 143 931.81 715

1.50 58 73 439.39 365

5.50 126 146 954.54 730

1.75 64 80 484.84 400

5.75 130 150 984.84 750

2.00 69 85 522.72 425

6.00 133 153 1007.57 765

2.25 74 90 560.6 450

6.25 136 156 1030.3 780

2.50 77 96 583.33 480

6.50 139 160 1053.03 800

2.75 81 100 613.63 500

6.75 142 164 1075.75 820

3.00 87 105 659.09 525

7.00 145 167 1098.48 835

3.25 91 110 689.39 550

7.25 148 170 1121.21 850

3.50 95 114 719.69 570

7.50 153 173 1159.09 865

3.75 99 118 750 590



Mass of Dry Soil + container (m3) g 234.7 231.1


2.5 mm 5

mm




Bottom 24 34.75

w = ((m2-m3)/(m3-m1)) * 100



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1.6 GRAPHICAL REPRESENTATION:

1.6.1 LOAD VS PENETRATION:

GRAPH # 01:

SAMPLE NO: 5 ML

GRAPH # 02:

SAMPLE NO: 10 ML

0

100

200

300

400

500

600

700

800

0 5 10 15 20 25 30 35

Lo

ad

KN

Penetration mm

0

200

400

600

800

1000

1200

1400

1600

1800

0 5 10 15 20 25 30 35

loa

d K

N

penetration mm

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GRAPH # 03:

SAMPLE NO: 15 ML

GRAPH # 04:

SAMPLE NO: 20 ML

0

100

200

300

400

500

600

700

800

900

1000

0 5 10 15 20 25 30 35

Lo

ad

KN

Penetration mm

0

200

400

600

800

1000

1200

1400

1600

1800

0 5 10 15 20 25 30 35

Lo

ad

KN

Penetration mm

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GRAPH # 05:

SAMPLE NO: 25 ML

1.6.2 CBR % VS DRY DENSITY:

GRAPH # 01:

0

200

400

600

800

1000

1200

1400

0 5 10 15 20 25 30 35

Lo

ad

KN

Penetration mm

0

10

20

30

40

50

60

70

80

90

100

3.05 3.1 3.15 3.2 3.25 3.3 3.35 3.4

CB

R %

Dry Density

Page | 14

1.6.3 CBR % VS MOISTURE CONTENT %:

1.6.4 DRY DENSITY VS MOISTURE CONTENT %:

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25

% C

BR

Moisture content %

0

5

10

15

20

25

3.05 3.1 3.15 3.2 3.25 3.3 3.35 3.4

Mo

istu

re

co

nte

nt %

Dry Density %

Page | 15

1.8 CONCLUSION & DISCUSSION:

In Highway and Pavement Design, it is very important to know the strength of sub grade soil, sub

base and base course materials. By using different tests, we can measure strength and thickness of

materials. We can measure the strength and thickness of materials in laboratory and also in field. We

use CBR Test to calculate required values. In this experiment we calculate CBR ratio, moisture content

% and dry density of different samples. Graphical representations of CBR ratio, moisture content %

and dry density also shown. A graph of load KN Vs. penetration (mm) is plotted when different

samples used. From the graph CBR ratio is found out. We get following results as

When sample no = 5 ml

� CBR % = 34.43%


� CBR % = 83.79%


� CBR % = 47.06%


� CBR % = 90.67%


� CBR % = 68.29%

Now from these values of CBR ratio, we can draw a graph of CBR ratio vs. dry density/moisture

content %.By using these theoretical and graphical values, we can calculate thickness of materials.

Documents

CBR TEST Practical