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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.
