The traffic for the design is considered in units of heavy vehicles (of laden weight exceeding 3 tons) per day in both directions and are divided into seven categories A to G. The suitable design curve should be chosen from the table given in the design chart (fig). The design thickness is considered for single axle loads upto 8,200 kg and random axle loads upto 14,500 kg. For higher axle loads the thickness values should be further increased. (This is improvement over earlier mentioned values of 8160 kg and 4080 kg) When sub-base course materials contain substantial proportion of aggregates of size above 20 mm, the CBR value of these materials would not be valid for the design of subsequent layers above them. This layers of wearing course such as surface dressing or open graded premixed carpet up to 2.5 cm thickness should not be counted towards the total thickness of pavement as they do not increase the structural capacity as the pavement.
2.5 TYPICAL PREASUMPTIVE VALUE OF CBR
Table- 3 (Typical presumptive CBR values)
CBR VALUE
SUBGRADE STRENGTH
3% or less
Poor
3% - 5%
normal
5% - 15%
good
CHAPTER – 3 DETAILS OF LABORATORY STUDIES
CHAPTER -3 DETAILS OF LABORATORY STUDIES 3.1 CALIFORNIA BEARING RATIO (The actual laboratory method) The CBR test was originally developed by O.J. Porter for the California Highway Department during the 1920s. It is a load-deformation test performed in the laboratory or the field, whose results are then used with an empirical design chart to determine the thickness of flexible pavement, base, and other layers for a given vehicle loading. Though the test originated in California, the California Department of Transportation and most other highway agencies have Since abandoned the CBR method of pavement design. In the 1940s, the US Army Corps of Engineers (USACE) adopted the CBR method of design for flexible airfield pavements. The thickness of different elements comprising a pavement is determined by CBR values. The CBR test is a small scale penetration test in which a cylindrical plunger of 3 in2 (5 cm in dia) cross-section is penetrated into a soil mass (i.e., sub-grade material) at the rate of 0.05 in. per minute (1.25 mm/minute). Observations are taken between the penetration resistance (called the test load) versus the penetration of plunger. The penetration resistance of the plunger into a standard sample of crushed stone for the corresponding penetration is called standard load. The California bearing ratio, abbreviated as CBR is defined as the ratio of the test load to the standard load, expressed as percentage for a given penetration of the plunger. CBR = (Test load/Standard load)×100 The table gives the standard loads adopted for different penetrations for the standard material with a CBR value of 100%.
Four Lot of soil samples of NH86 Bhopal to Chhatarpur Road taken as per classification. Samples are molded at its optimum moisture content to its proctor density was tested for its soaked and unsoaked CBR strength and also carried out IS classification as per IS 2720 and wet sieve analysis also carried out by four soil sample. Thus the process comprises of three parts. 1.
On original sample carried out first wet sieve analysis, liquid limit and plastic limit.
2.
Estimation of proctor density and optimum moisture content for each soil sample.
3.
Molding the soil sample into standard moulds keeping its moisture content and dry density exactly same as its optimum moisture content and proctor density respectively.
4.
Determination of CBR strength of the respective soil samples in moulds using the CBR instrument.
5. Each soil sample is tested for its soaked CBR and unsoaked CBR strength after soaked in water for 4 days
being
The experimental work comprises in the following parts:
3.2
Determination of index property
Liquid limit by liquid limit device
Plastic limit
Plastic Index
Shrinkage limit
3.2.1 Liquid Limit Test This test is done to determine the liquid limit of soil as per IS: 2720 (Part 5) – 1985. The liquid limit of fine-grained soil is the water content at which soil behaves practically like a liquid, but has small shear strength. Its flow closes the groove in just 25 blows in Casagrande’s liquid limit device.
3.2.2 Plastic Limit Test Plastic limit is defined as minimum water content at which soil remains in plastic state. The plasticity index is defined as the numerical difference between its Liquid limit and Plastic limit.
3.3 Determination of CBR of Soil (i)
Moulding the soil sample into standard moulds keeping its moisture content and dry density exactly same as its optimum moisture content and proctor density respectively.
(ii)
Determination of CBR strength of the respective soil samples in moulds using the CBR instrument.
(iii) Soil sample is tested for its CBR strength after being soaked in water for 1 day, 2 days, 3 days and 4 days. Unsoaked CBR is also determined for each sample.
CHAPTER – 4 ANALYSIS & RESULTS
CHAPTER - 4 ANALYSIS & RESULTS FOUR Lot of collected soil samples are moulded at its optimum moisture content to its proctor density was tested for its soaked and unsoaked CBR strength and also carried out IS Classification.
4.1 ANALYSIS & RESULT OF SAMPLE NO. 1
The result of CBR test of soil sample performed in the laboratory under different times of soaking are presented in table no. 4
Table No. 4 (Analysis & Result of sample No. 1) Atterberg’s Limit
Liquid Limit (LL) %
Plastic Limit (PL) %
Plasticity Index (PI) %
Free Swell Index
Mas Dry Density gm/cc
OMC%
CBR Unsoaked (0 Hrs.)
38.40
20.53
17.87
24.5
1.9
12
18.57
Observation Reports of Sample No. 1 are given below :1. Grain Size Analysis 2. Consistency Limit 3. Free Swell Index 4. MDD & OMC 5. CBR Unsoaked 6. CBR Soaked
CBR soaked (24 Hrs.)
CBR soaked (48 Hrs.)
CBR soaked (72Hrs.)
CBR with 4 day Soaking
9.66
7.14
6.05
5.02
Table No.5 (Grain size analysis of sample no. 1)
Fig. No. 2 (LL & PL Test Result of sample no. 1
Fig. No. 3 (CBR Test Result (0 Hrs.) of sample no. 1)
Fig. No. 4 (CBR Test Result (24Hrs.) of sample no. 1)
Fig. No. 5 (CBR Test Result (48 Hrs.) of sample no. 1)
Fig. No. 6 (CBR Test Result (72Hrs.) of sample no. 1
CBR with 96 Hrs. Soaking Sample No. 1
Fig. No. 7 (CBR Test Result (96 Hrs.) of sample no. 1
VARIATION OF CBR WITH TIME OF SOAKING SAMPLE NO. 1
CBR Unsoaked (0 Hrs.)
CBR soaked (24 Hrs.)
CBR soaked (48 Hrs.)
CBR soaked (72Hrs.)
CBR with 4 day Soaking (96 Hrs.)
18.57
9.66
7.14
6.05
5.02
20.00 18.00 16.00 14.00 )
% n i
12.00 10.00
R B C 8.00 6.00 4.00 2.00 0.00
0.0
20.0
40.0
60.0
80.0
100.0
Time in Hour's
Fig. No. 8 (Variation of CBR with Time of Soaking Sample No. 1)
120.0
4.2 ANALYSIS & RESULT OF SAMPLE NO. 2 The result of CBR test of soil sample performed in the laboratory under different times of soaking are presented in table no. 6
Table No. 6 (Analysis of Sample No. 2)
Atterberg's Limit
Liquid Limit (LL) %
Plastic Limit (PL) %
Plasticity Index (PI) %
34.50
20.53
13.97
Free Swell Index
Mas Dry Density gm/cc
29.25
1.9
OMC%
CBR Unsoaked (0 Hrs.)
CBR soaked (24 Hrs.)
CBR soaked (48 Hrs.)
CBR soaked (72Hrs.)
CBR with 4 day Soaking
12
25.25
13.37
10.40
7.35
6.19
Observation Reports of Sample No. 2 are given below :1. Grain Size Analysis 2. Consistency Limit 3. Free Swell Index 4. MDD & OMC 5. CBR Unsoaked 6. CBR Soaked
Table No. 7 (Grain Size Analysis of sample no. 2
Fig. No. 9 (LL & PL Test Result of sample no. 2
Fig. No. 10 (CBR Test Result (0 Hrs.) of sample no. 2
Fig. No. 11 (CBR Test Result (24 Hrs.) of sample no. 2
Fig. No. 12 (CBR Test Result (48 Hrs.) of sample no. 2
Fig. No. 13 (CBR Test Result (72 Hrs.) of sample no. 2
CBR with 96 Hrs. Soaking Sample No. 2
Fig. No. 14 (CBR Test Result (96 Hrs.) of sample no. 2
VARIATION OF CBR WITH TIME OF SOAKING SAMPLE NO. 2 CBR Unsoaked (0 Hrs.)
CBR soaked (24 Hrs.)
CBR soaked (48 Hrs.)
CBR soaked (72Hrs.)
CBR with 4 day Soaking (96 Hrs.)
25.25
13.37
10.40
7.35
6.19
30.00
25.00
20.00 )
% n i R B C
15.00
10.00
5.00
0.00 0.0
20.0
40.0
60.0
80.0
100.0
Time in Hour's
Fig. No. 15 (Variation of CBR with time of Soaking Sample No. 2)
120.0
4.3 ANALYSIS & RESULT OF SAMPLE NO. 3
The result of CBR test of soil sample performed in the laboratory under different times of soaking are presented in table no. 8
Table No. 8 (Analysis of sample no. 3) Atterberg's Limit
Liquid Limit (LL) %
Plastic Limit (PL) %
Plasticity Index (PI) %
33.26
20.53
12.73
Free Swell Index
Mas Dry Density gm/cc
16.3
1.87
OMC%
CBR Unsoaked (0 Hrs.)
CBR soaked (24 Hrs.)
CBR soaked (48 Hrs.)
CBR soaked (72Hrs.)
CBR with 4 day Soaking
9
21.54
12.63
11.88
10.40
8.37
Observation Reports of Sample No. 3 are given below :1. Grain Size Analysis 2. Consistency Limit 3. Free Swell Index 4. MDD & OMC 5. CBR Unsoaked 6. CBR Soaked
Table No. 9 (Grain size analysis of sample no. 3)
Fig. No. 16 (LL & PL Test Result of sample no. 3
Fig. No. 17 (CBR Test Result (0 Hrs.) of sample no. 3
Fig. No. 18 (CBR Test Result (24 Hrs.) of sample no. 3
Fig. No. 19 (CBR Test Result (48 Hrs.) of sample no. 3
Fig. No. 20 (CBR Test Result (72 Hrs.) of sample no. 3
Fig. No. 21 (CBR Test Result (96 Hrs.) of sample no. 3
VARIATION OF CBR WITH TIME OF SOAKING SAMPLE NO. 3
CBR Unsoaked (0 Hrs.)
CBR soaked (24 Hrs.)
CBR soaked (48 Hrs.)
CBR soaked (72Hrs.)
CBR with 4 day Soaking (96 Hrs.)
21.54
12.63
11.88
10.40
8.37
30.00
25.00
20.00 )
% n i R B C
15.00
10.00
5.00
0.00 0 .0
2 0 .0
4 0 .0
6 0 .0
8 0 .0
1 0 0 .0
Time in Hour's
Fig. No. 22 (Variation of CBR with time of Soaking Sample No. 3)
1 2 0 .0
4.4 ANALYSIS & RESULT OF SAMPLE NO. 4 The result of CBR test of soil sample performed in the laboratory under different times of soaking are presented in table no. 10
Table No. 10 (Analysis of sample No. 4)
Atterberg's Limit
Liquid Limit (LL) %
Plastic Limit (PL) %
Plasticity Index (PI) %
31.53
20.53
11.00
Free Swell Index
Mas Dry Density gm/cc
19.3
1.93
OMC%
CBR Unsoaked (0 Hrs.)
CBR soaked (24 Hrs.)
CBR soaked (48 Hrs.)
CBR soaked (72Hrs.)
CBR with 4 day Soaking
10
17.83
9.66
8.91
7.43
5.31
Observation Reports of Sample No. 4 are given below :1. Grain Size Analysis 2. Consistency Limit 3. Free Swell Index 4. MDD & OMC 5. CBR Unsoaked 6. CBR Soaked
Table No. 11 (Grain Size Analysis of sample No 4)
Fig. No. 23 (LL & PL Test Result of sample no. 4
Fig. No. 24 (CBR Test Result (0 Hrs.) of sample no. 4
Fig. No. 25 (CBR Test Result (24 Hrs.) of sample no. 4
Fig. No. 26 (CBR Test Result (48 Hrs.) of sample no. 4
Fig. No. 27 (CBR Test Result (72Hrs.) of sample no. 4
CBR with 96 Hrs. Soaking Sample No. 4
Fig. No. 28 (CBR Test Result (96 Hrs.) of sample no. 4
VARIATION OF CBR WITH TIME OF SOAKING SAMPLE NO.4
CBR Unsoaked (0 Hrs.)
CBR soaked (24 Hrs.)
CBR soaked (48 Hrs.)
CBR soaked (72Hrs.)
CBR with 4 day Soaking (96 Hrs.)
17.83
9.66
8.91
7.43
5.31
20.00 18.00 16.00 14.00 )
% 12.00 n i 10.00
R B 8.00 C 6.00 4.00 2.00 0.00 0.0
20.0
40.0
60.0
80.0
100.0
Time in Hour's
Fig. No. 29 (Variation of CBR with time of Soaking Sample No. 4)
120.0
CHAPTER - 5 CONCLUSIONS & RECOMMANDATION FOR FUTHER STUDY
5.1 CONCLUSION From the results and discussions described earlier, it is observed that the CBR value of the given soil sample decreases rapidly with time of soaking up to 24 hrs. and then decreases slowly. When soil samples are taken from different points of the CBR sample and tested This Study is an attempt to understand the influence of soaking on CBR value subjected to different days of soaking and the corresponding variation in moisture content. It is observed that the CBR decreases and the moisture content increases for high degree of soaking.
5.2 RECOMMANDATION FOR FUTHER STUDY It is recommended that more studies on different type of soil prevailing in studies to be conducted involving large number of samples.
Table No. 12 (Variation of CBR with time of soaking of sample no 1 to 4)
Sample No.
CBR result (0 Hrs.)
CBR result (24 Hrs.)
CBR result (48 Hrs.)
CBR result (48 Hrs.)
CBR result (72 Hrs.)
CBR result (96 Hrs.)
1
18.57
9.66
7.14
7.14
6.05
5.02
2
25.25
13.37
10.4
10.4
7.35
6.19
3
21.54
12.63
11.88
11.88
10.4
8.37
4
17.83
9.66
8.91
8.91
7.43
5.31
Fig. No. 30 (Variation of CBR with time of soaking of sample no 1 to 4)
REFERENCES Arora K.R. “A Text book of Soil Mechanics”
Bindra S.P. "A Text Book of Highway Engineering" Dhanpat Rai Publications, New Delhi
Berry D.S. K.B. and Goetz Woods, W.H. Highway Engineering Hand Book, McGraw Hill Book Co. Inc. India.
Khanna S.K. and C.E.G. Justo, Nem Chand & Bros; Roorkee Highway engineering.
Mathew V. Tom , (2009), Entitled "Pavement materials: Soil Lecture notes in Transportation Systems Engineering.
Punmia B.C., Ashok Kumar Jain & Arun Kumar Jain “A Text Book of Soil Mechanics &
Foundations”.
Sahoo Biswajeet & Nayak Devadatta, (2009) "A Study of Subgrade Strength Related to moisture"
Singhal, R.P. (1967). Soil Mechanics and Foundation Engineering, Singhal Publications, India.
Terzaghi, K. (1943). Theoretical soil Mechanics, Chapman and Hall, London and John Wiley & Sons.
Terzaghi, K. and Peck, R.B. (1967). Soil M echanics in engineering practice, Hohn Wiley & Sons.
Yoder, E.J., Principles of pavement design, John Wiley and Sons, India.
“Guidelines for the Design of Flexible Pavements for low volume of Rural road”
IRC- SP-72,
IS 2720 Part-5 “Method of test for Soil- Determination of Liquid limit and Plastic limit”
IS 2720 Part –8 “Method of test for Soil-Determination of Water Content, Dry density relation using a heavy Compaction”
