Cbr Lab Report 96241

CALCULATION Following was observed: Sample type : distrurbed Compaction of specimen: Dynamic with IS heavy compaction Weight of rammer: 4.89 kg No.of blows :56 nos Layers of compaction :5 layers Surcharge wt.placed: 2.9 kg Condition of specimen :soaked Soaking period :4 days Compacting Moisture content: optimum moisture content dry density at OMC Proving ring conversion Factor :no .of smallest div.of dial gauge x1.282 kgf Diameter of plunger : 5 mm Area of plunger: π x50²/4=1963.5 mm²

A. Before Soaking : Moisture content and dry density determination:

Mould No. Container No. Wt. of container with wet soil (X)gm.

1 68

Wt.of container with dry soil (Y) gm.

62

Wt. Of empty container (Z) gm.

9

Wt. Of water (Wʷ)gm. Wt. Of dry soil (Wᵈ)gm. Moisture content (m)= Wʷ/Wᵈ X100 Volume of mould (Vm)cc Wt.of mould (Wm) gm Wt. Of mould + compacted soil (Wbs)gm

3092.50 cc 3300 9675

Wt. Density (Vm)=(Wbs-Wm)/Vm(gm/cc)

2.061

Dry density (Vᵈ)=Vm/(1+m)(gm/cc)

1.85

A 2

3

6 53 11.32

B. After Soaking : Mould No. Wt. Of mould (Wm) kg Wt. Of mould + compacted soil after soaking (Wbs) kg Wt. Of mould + compacted soil after (Was) kg Initial reading of the dial gauge of swell assembly (di) mm Final reading of the dial gauge of swell assembly (df) mm Initial height of specimen (h) mm Water absorbed (Ww) = (Was-Wbs)/(WbsWm)X100 Expansion ratio (Er)= (df-di)/hX100

1 3.30 9.675 9.915 0 55 x 0.25 =13.75 mm 127.3 3.76 10.80

OBSERVATION DURING PENETRATION AND DETERMINATION OF CBR: S.no

Penetration

Standard Load

Proving ring dial

Load on plunger (Pt)=

(Y) (mm)

value (P)(kgf)

gauge reading

RxF= Rx1.282 (kgf)

1

0

(R) 0

0

2

0.5

22

28.204

3 4 5

1 2 2.5

40 78 92

51.28 99.996 117.944

6

3.5

110

141.02

7

4

116

148.712

8

5

130

166.66

9

7.5

154

197.428

10

10

3180

170

217.94

11

12.4

3600

181

232.042

1370

2055

Calculation and finding after plotting the graph of CBR s.no

Penetration n (Y)

Standard load

Value of load

CBR = (Pg/Ps)x

mm

value (Ps)kgf

from graph

100

1

2.5

1370

(pg)kgf 117.944

2

5

2055

166.66

8.609 8.110

Result: From the moisture content determine graph the optimum moisture content of the soil sample was found to be 11.32 %. And from the load penetration graph, the value of load from graph

corresponding to penetration of 2.5 mm and 5.0 mm are calculated and obtained as 117.944 kgf and 166.66 kgf respectively.The CBR value of the soil is found to be 8.6% i.e higher of these two values.

Conclusion Normally the CBR value at 2.5 mm penetration whic is higher than at 5.0 mm penetration which is reported as the CBR value of material . However,here we abtained that the CBR

value at 2.5 mm penetration is higher than that obtained at 5.0 mm penetration . The general procedure is if this criterion doesnot fulfill by the test should be again repeated and if the value of CBR at 5.0 mm again comes more than 2.5 mm penetration then the higher value of the three test specimen is reported as the CBR value. There may be certain errors for the initial concavity of the load-penetration curve are: a. The bottom surface of the plunger or the top surface of the soil specimen not being trully horizontal,with the result the plunger surface not being in full specimen initially and, b. The top layer of the specimen being too soft or irregular . c. There may be error in loading at a rate of 1.25 mm/ minute A correction is applied for curves curving concavity upwards. A tangent is drawn from the steepest portion of curve to intersect the x-axis as which is the origin for this specimen. The penetration value are measured from this corrected origin . Minimum two sample should be made and test for CBR ,but we test only one sample which is not the basic rule we followed. So we have to test at least for two sample specimen and the result should be taken as mean of two which is reported as CBR value of this sample after correcting if error in curve occurs.According to indian standard soil code the CBR value between 8 to 20 falls in the range of well graded sand ,our result within this range. For the optimum moisture content at least three sample should be tested but we test only one sample which is not correct OMC value of this subgrade soil. Hance i conclude that the soil sample is well graded sand and the CBR test should be again done for the correct result and conformation of single sample obsevation data. This CBR value is more useful for the fiexible pavement design of roads.

References 1. http://www.docstoc.com/docs/84748462/CALIFORNIA-BEARING-RATIO-_-CBR-_TEST 2. http://www.youtube.com/watch?v=8mdSmB3CtZM

3. http://www.outbackroads.com/reports/4th_type_2_trial_test_CBR.pdf 4. http://www.aboutcivil.org/california-bearing-ratio-test.html

Table of Contents Item

No 1.

Introduction

2.

Objectives

3.

Equiments

4.

Procedure

5.

Result

Pages

6.

Calculation

7.

Discussion

8.

Conclusion

9.

References