California Bearing Ratio Cbr

Published Date: 02 Nov 2017

Laboratory Report

Student Number:

B Eng. Civil Engineering 2007 - 2008

CE2204 Geo-mechanics

Lecturer: R J Freeman

Date of experiment: 8/4/08

Contents

Aim of the experiment……………………………………….........…page 3

Apparatus……………………………………………….……...….….page 3

Procedure…………………………………………………….....…….page 4

Observations…………………………………………………....…….page 5

Graph…….....................…………………………………………......page 7

Calculations...................................................................................page 7

Results ………………………………………………….……………..page 9

Discussion ..............……………………………………….…………page 9

Conclusion…………………………………………………….……….page 9

10) References……………………………………………………….…..page 9

1) Aim of the experiment

The aim of this laboratory test is to determine the California Bearing Ratio for a given soil sample in accordance with BS 1377 Test 16.

2) Apparatus

Figure 1 - sketch of the soil compaction machine and the mould with its critical dimensions

Figure 2 - sketch of the CBR machine

3) Procedure

The diameter, the height and the mass of the empty CBR mould without its collar were measured.

The mass of an empty tin was measured.

6 kg of soil were mixed on a tray with 420ml of water to give a moisture content of 7%.

The soil was devided into three parts.

The collar was placed on the mould and the mould placed in the compaction machine.

The first part of the soil was added and compacted with 62 blows. Then the second part and then the third. Each of them compacted with 62 blows.

The collar was removed from the mould and the top of the sample was trimmed.

The mass of the mould containing the compacted soil was measured.

The mould with the compacted soil was placed in the CBR testing machine.

The surcharge masses were placed on the sample to prevent it from getting out of the mould during the testing.

The plunger was set under a force of 50N.

The dial gauge was zeroed and the machine was turned on.

The reading was taken every 12 seconds.

The mould was removed from the machine and the hole which was made by the plunger on the surface of the soil sample was filled and trimmed. Then the mould was turned upside down and placed again in the testing machine to be tested from that side too.

After the test was finished a tin was filled with the soil sample in two layers each of them taken from the two sides of mould that were tested.

The mass of the tin with the soil was measured.

The soil was dried in the oven for about 24 hours and its mass was measured again.

4) Observations

mass of empty mould without collar: 10863.5g

7% water content: 420ml water

weight of mould with soil (hogin): 16071.0g

diameter of mould: 15.2cm

height of mould without collar: 12.6cm

tin number: 02

weight of empty tin: 17.7

weight of tin + wet soil: 205.2

weight of tin + dry soil: 196.6g

Table 1 - Raw results

time (sec)

top of mould

bottom of mould

reading

reading

0

0

0

12

2

2

24

4

4

36

6

6.5

48

8.5

9

60

12

10

72

14.5

14

84

17

17

96

21

20

108

24.5

24

120

28

28

132

31

32

144

33

36.5

156

41

41

168

46

47

180

50

50

192

57

56

204

63

61

216

68

65

228

73

71

240

80

76

252

87

84

264

92

90

276

100

95

288

106

102

300

108

109

312

119

113

324

125

121

336

128

125

348

137

131

360

146

136

Table 2 – Analyzed Results

time (sec)

First test (Top of mould)

Second test (bottom of mould)

penetration (mm)

reading

plunger (mm)

Force (kN)

reading

plunger (mm)

Force (kN)

0

0

0

0.000

0

0

0.000

0.00

12

2

0.02

0.254

2

0.02

0.254

0.20

24

4

0.04

0.508

4

0.04

0.508

0.40

36

6

0.06

0.762

6.5

0.065

0.825

0.60

48

8.5

0.085

1.079

9

0.09

1.143

0.80

60

12

0.12

1.524

10

0.1

1.270

1.00

72

14.5

0.145

1.841

14

0.14

1.778

1.20

84

17

0.17

2.159

17

0.17

2.159

1.40

96

21

0.21

2.667

20

0.2

2.540

1.60

108

24.5

0.245

3.111

24

0.24

3.048

1.80

120

28

0.28

3.556

28

0.28

3.556

2.00

132

31

0.31

3.937

32

0.32

4.063

2.20

144

33

0.33

4.190

36.5

0.365

4.635

2.40

156

41

0.41

5.206

41

0.41

5.206

2.60

168

46

0.46

5.841

47

0.47

5.968

2.80

180

50

0.5

6.349

50

0.5

6.349

3.00

192

57

0.57

7.238

56

0.56

7.111

3.20

204

63

0.63

8.000

61

0.61

7.746

3.40

216

68

0.68

8.580

65

0.65

8.232

3.60

228

73

0.73

9.159

71

0.71

8.928

3.80

240

80

0.8

9.971

76

0.76

9.507

4.00

252

87

0.87

10.783

84

0.84

10.435

4.20

264

92

0.92

11.362

90

0.9

11.130

4.40

276

100

1

12.290

95

0.95

11.710

4.60

288

106

1.06

12.986

102

1.02

12.522

4.80

300

108

1.08

13.217

109

1.09

13.333

5.00

312

119

1.19

14.493

113

1.13

13.797

5.20

324

125

1.25

15.188

121

1.21

14.725

5.40

336

128

1.28

15.536

125

1.25

15.188

5.60

348

137

1.37

16.559

131

1.31

15.884

5.80

360

146

1.46

17.566

136

1.36

16.448

6.00

7) Graph

5) Calculations

For the "standard" CBR soil:

Penetration (mm)

Resistance (kN)

2.5

13.2

5.0

20.0

Force required for 2.5 penetration in 1st test soil (top of mould): 4.58kN

Force required for 5.0 penetration in 1st test soil (top of mould): 13.217kN

So for the first test soil the CBR values are:

CBR2.5 = 4.58 x 100 = 34.69%

13.2

CBR5.0= 13.217 x 100 = 66.09%

20.0

Force required for 2.5 penetration in 2nd test soil (bottom of mould): 4.83kN

Force required for 5.0 penetration in 2nd test soil (bottom of mould): 13.333kN

So for the second test soil the CBR values are:

CBR2.5 = 4.83 x 100 = 36.59%

13.2

CBR5.0= 13.333 x 100 = 66.67%

20.0

Mass of the soil sample: (Weight of the mould with soil) –

(Weight of the mould without collar) 16.071 – 10.863.5= 5.2075kg

Mould Volume (V): = 9.14

Bulk Density: p= = 570kg/m3

Moisture Content: Tin No02 = (205.2-196.6)/205.2=0.0872=4.2%

6) Results

soil

top

bottom

CBR2.5

34.69%

36.59%

CBR5.0

66.09%

66.67%

8) Discussion

The forces at table 2 were determined by interpolation from a table given in the laboratory. The curves of the two soils on the graph are continiously concave upwards so there is no need to correct zero for both soils. The CBR values were calculated by using the resistance of the soils for penetrations of 2.5mm and 5.0mm.

9) Conclusions

During this lab experiment some errors may have occured during the procedure as the readings of the CBR machine had to be taken every 12 seconds which could not happen accurately. These errors could be eliminated if the procedure was done more carefully.