Laith Hussain Highway laboratory

Republic of
Iraq

The Ministry
of Higher

Education and
Scientific

Research

University of
Karbala
Name of exp.:
College of

Civil
Engineering

Evening study
Number of exp.:
Fourth stage

Laboratory of Date of exp.:

Highway

2018/12/6

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Introduction:

The CBR test was originally developed by O. J. Porter for the California Highway
Department during the 1920s. It is a load-deformation test per-formed in the
laboratory or field; results are then used with empirical de-sign charts 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 high-way agencies have abandoned the CBR
method of pavement design for the Hveem stabilometer and other methods
(Oglesby and Hicks 1982). In the 1940s, USACE adopted the CBR method of
design for flexible airfield pavements and USACE and USAF design practice for
surfaced and unsurfaced airfields is still based on CBR today (U.S. Army and Air
Force 1994b).

CBR may be performed either in the laboratory, typically with a recompacted

sample, or in the field. The laboratory CBR test method is defined by ASTM D
1883-05 (American Society for Testing and Materials 2005). Because of typical
logistical and time constraints, the laboratory test does not lend itself to use for
contingency road and airfield design. In-situ CBR tests are also time-consuming to
run and are usually impractical for use in theater (U.S. Army and Air Force
1994b). To address the concerns with the standard CBR tests, the military has
adopted other tools more suited for field operations. The airfield cone penetrometer
and the dual mass DCP are most typically used in the field, and correlations are
provided to trans-late their measurements into CBR values for use in design (U.S.
Army and Air Force 1994b). Historically, however, there is a great deal of directly
measured field CBR information available.

The field CBR test procedure is described in ASTM D 4429-04 (American Society
for Testing and Materials 2004) and Army FM 5-530 (U.S. Army, Air Force, and
Navy 1987). The field CBR test is performed by measuring the penetration
resistance of a 1.954-in.-diameter (3-in.2 end area) cylindrical steel piston
advanced into the soil at a rate of 0.05 in. /min. The re-action force is measured, by
means of a calibrated proving ring, at increments of 0.025 in. until a total
penetration of 0.500 in. is reached.

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To determine the CBR value, the reaction forces measured at 0.100- and 0.200-in.
penetration are compared to standardized values of 1,000 and 1,500 pounds per
square inch (psi), respectively. These represent the resistance of a high-quality,
well-graded crushed limestone gravel with ¾-in. maximum aggregate-sized
particles. The values of two forces measured in the test are divided by their
respective standardized value, and then multi-plied by 100, to yield two index
values. The larger of the two values is re-ported as the CBR of the soil, in percent.

The CBR test method is most appropriate and gives the most reliable results for
fine-grained soils. It can also be used to characterize the strength of soil-aggregate
mixtures (e.g., subbases) and unbound aggregate base courses. In cohesionless
soils, especially ones that include large particles, the reproducibility of the test is
poor (Rollings and Rollings 1996). In the laboratory test procedure, test samples
are prepared with soils of aggregate particle size of less than ¾ in. In the case of
soils where particle sizes greater than ¾ in. exist, the large particles are removed
from the sample and replaced with an equal mass of material that falls between the
¾-in. sieve and the number 4 (4.75-mm) sieve sizes. In the field CBR test
procedure, removal of larger particles that may adversely affect the test results is
not possible, and therefore these types of soils are likely to produce un-reliable
results.

There are several existing methods for predicting CBR values for soils based on
soil classification, soil characteristics, and soil index test values. Semen (2006)
discusses several approaches to CBR prediction:

1. CBR values by soil type based on the USCS. From the literature, Semen
summarized CBR values based on the specific soil type as defined by the
USCS as shown in Table 1. Letter symbols for the USCS soils designations
are defined in Table 2. The relationship be-tween CBR and USCS soil
classification is schematically.

2. Mechanistic-Empirical Design for New and Rehabilitated Pavement

Structures as developed under the National Cooperative Highway Research
Program (NCHRP) (2004) uses a simple regression to predict CBR based on
grain-size characteristics for non-plastic soils, and grain size and plasticity
index for plastic soils.
3. Soil strength “signature” concept combines laboratory results from CBR and
standard moisture-density tests (known as Proctor curves) to provide a
relation between CBR, compaction, and molded moisture content (Rada et
al. 1989).
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4. Joint Rapid Airfield Construction (JRAC) program in progress is developing

a prediction model for CBR based on moisture content and compaction
levels, for different USCS soil types. This approach is also based on
regression analysis (Berney 2008).
Semen (2006) also discusses several site-specific or specialized prediction
models, where soils from a specific location or region have been sampled
and tested to determine CBR relationships specific to those soils. The
equations developed include terms for field dry density, moisture content,
plasticity index, and liquid limit, among others. These approaches, though
developed to work in specific locations, may also have application in a
global database and prediction model.
Standard Reference
Standard Test Method for CBR (California Bearing Ratio) of Laboratory-
Compacted Soils D1883.

Calculation & Results:

Mold Number: 25/H OR 10/B

Height of the mold (h) = 18 cm
Diameter of the mold (D) = 15.5 cm
Height of Disk=6.25cm
Height of Sample=18-6.25=11.275cm
𝜋𝜋
𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉 𝑜𝑜𝑜𝑜 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 (𝑉𝑉) = × 𝐷𝐷2 × h
4
𝜋𝜋
𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉 𝑜𝑜𝑜𝑜 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 (𝑉𝑉) = × 15.52 × 11.75 ≅ 2216 𝑐𝑐𝑐𝑐3
4
The weight of the mold is empty without the top part (W1) = 7420 g
The weight of the mold with soil before immersion with water (W2) = 12137 g
Weight of the mold with soil after immersion with water = 12163 g
Number of tin =96

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Weight of empty tin (W3) = 21g

Weight of tin with wet soil (W4) = 76.57g
Weight of tin with dry soil (W5) = 71.45g
W4 − W5
𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶% = × 100
W5 − W3
76.57 − 71.45
𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶% = × 100 ≅ 10.15% = 0.1015
71.45 − 21
W2 − W1
ᵞ𝑤𝑤𝑤𝑤𝑤𝑤 =
𝑉𝑉
12137−7420
ᵞ𝑤𝑤𝑤𝑤𝑤𝑤 = ≅ 2.129 g/cm3
2216

ᵞ𝑤𝑤𝑤𝑤𝑤𝑤
ᵞ𝑑𝑑𝑑𝑑𝑑𝑑 =
1 + 𝑤𝑤𝑐𝑐
2.129
ᵞ𝑑𝑑𝑑𝑑𝑑𝑑 = ≅ 1.933 g/cm3
1+0.1015
𝜋𝜋
Area of piston = × 4.9632 = 19.3365 cm2
4

Stander stress at 2.5mm = 6.9 𝑀𝑀𝑀𝑀𝑀𝑀

Stander stress at 5mm = 10.3 𝑀𝑀𝑀𝑀𝑀𝑀
Penetration (mm) Load (Kg) Stress (Mpa)
0.64 3 0.015
1.27 4.5 0.023
1.91 6.5 0.033
2.54 8 0.041
3.18 11.5 0.058
3.81 15.5 0.079
4.45 29 0.147
5.08 34 0.172
7.62 80 0.405
10.16 159.5 0.808
12.7 275.5 1.396

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CBR
1.600
1.396
1.400

1.200

1.000
0.808
0.800

0.600
0.405
0.400
0.041
0.023
0.147
0.200 0.079
0.033 0.058 0.172
0.015
0.000
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

10 Blows

Stress for 2.5mm Penration =0.04 Mpa

Stress for 5mm Penration =0.16 Mpa

Stress for 2.5mm Penration

%CBR 2.5 = ∗ 100
Stander stress at 2.5mm
0.04
%CBR 2.5 = ∗ 100 = 0.5797
6.9
Stress for 5mm Penration
%CBR 5 = ∗ 100
Stander stress at 5mm
0.16
%CBR 5 = ∗ 100 = 1.5534
10.3
∴ 𝐶𝐶ℎ𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜 𝐶𝐶𝐶𝐶𝐶𝐶 = 1.5534

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Mold Number: 10/Eb

Height of the mold (h) = 18 cm
Diameter of the mold (D) = 15.5 cm
Height of Disk=6.25cm
Height of Sample=18-6.25=11.275cm
𝜋𝜋
𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉 𝑜𝑜𝑜𝑜 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 (𝑉𝑉) = × 𝐷𝐷2 × h
4
𝜋𝜋
𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉 𝑜𝑜𝑜𝑜 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 (𝑉𝑉) = × 15.52 × 11.75 ≅ 2216 𝑐𝑐𝑐𝑐3
4
The weight of the mold is empty without the top part (W1) = 7053 g
The weight of the mold with soil before immersion with water (W2) = 11887 g
Weight of the mold with soil after immersion with water = 11896 g
Number of tin =2
Weight of empty tin (W3) = 18.18g
Weight of tin with wet soil (W4) = 66.24g
Weight of tin with dry soil (W5) = 61.14g
W4 − W5
𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶% = × 100
W5 − W3
66.24 − 61.14
𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶% = × 100 = 11.87% = 0.1187
61.14 − 18.18
W2 − W1
ᵞ𝑤𝑤𝑤𝑤𝑤𝑤 =
𝑉𝑉
11887−7053
ᵞ𝑤𝑤𝑤𝑤𝑤𝑤 = = 2.1814 g/cm3
2216

ᵞ𝑤𝑤𝑤𝑤𝑤𝑤
ᵞ𝑑𝑑𝑑𝑑𝑑𝑑 =
1 + 𝑤𝑤𝑐𝑐
2.1814
ᵞ𝑑𝑑𝑑𝑑𝑑𝑑 = = 1.95 g/cm3
1+0.1187

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𝜋𝜋
Area of piston = × 4.9632 = 19.3365𝑐𝑐𝑐𝑐2
4
Stander stress at 2.5mm = 6.9 𝑀𝑀𝑀𝑀𝑀𝑀
Stander stress at 5mm = 10.3 𝑀𝑀𝑀𝑀𝑀𝑀
Penetration (mm) Load (Kg) Stress (Mpa)
0.64 31.5 0.160
1.27 47 0.238
1.91 65 0.329
2.54 81.5 0.413
3.18 97 0.492
3.81 114.5 0.580
4.45 131.5 0.666
5.08 155 0.786
7.62 219 1.110
10.16 348 1.764
12.7 476 2.412

CBR
3.000

2.412
2.500

2.000 1.764

1.500
1.110
1.000 0.786
0.492
0.238
0.500 0.329 0.666
0.160 0.580
0.413
0.000
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

25 Blows

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Stress for 2.5mm Penration =0. 4 Mpa

Stress for 5mm Penration =0.77 Mpa

Stress for 2.5mm Penration

%CBR 2.5 = ∗ 100
Stander stress at 2.5mm
0.4
%CBR 2.5 = ∗ 100 = 5.797
6.9
Stress for 5mm Penration
%CBR 5 = ∗ 100
Stander stress at 5mm
0.77
%CBR 5 = ∗ 100 = 7.476
10.3
∴ 𝐶𝐶ℎ𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜 𝐶𝐶𝐶𝐶𝐶𝐶 = 7.476

Mold Number: 25/A OF 56/Q

Height of the mold (h) = 18 cm
Diameter of the mold (D) = 15 cm
Height of Disk=6.25cm
Height of Sample=18-6.25=11.275cm
𝜋𝜋
𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉 𝑜𝑜𝑜𝑜 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 (𝑉𝑉) = × 𝐷𝐷2 × h
4
𝜋𝜋
𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉 𝑜𝑜𝑜𝑜 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 (𝑉𝑉) = × 152 × 11.75 ≅ 2075.344 𝑐𝑐𝑐𝑐3
4
The weight of the mold is empty without the top part (W1) = 8300 g
The weight of the mold with soil before immersion with water (W2) = 13150 g
Weight of the mold with soil after immersion with water = 13146 g
Number of tin =S002

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Weight of empty tin (W3) = 11g

Weight of tin with wet soil (W4) = 44g
Weight of tin with dry soil (W5) = 41.48g
W4 − W5
𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶% = × 100
W5 − W3
44 − 41.48
𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶% = × 100 = 8.268% = 0.08268
41.48 − 11
W2 − W1
ᵞ𝑤𝑤𝑤𝑤𝑤𝑤 =
𝑉𝑉
13150−8300
ᵞ𝑤𝑤𝑤𝑤𝑤𝑤 = = 2.337 g/cm3
2075.344

ᵞ𝑤𝑤𝑤𝑤𝑤𝑤
ᵞ𝑑𝑑𝑑𝑑𝑑𝑑 =
1 + 𝑤𝑤𝑐𝑐
2.337
ᵞ𝑑𝑑𝑑𝑑𝑑𝑑 = = 2.1585 g/cm3
1+0.08268
𝜋𝜋
Area of piston = × 4.9632 = 19.3365𝑐𝑐𝑐𝑐2
4
Stander stress at 2.5mm = 6.9 𝑀𝑀𝑀𝑀𝑀𝑀
Stander stress at 5mm = 10.3 𝑀𝑀𝑀𝑀𝑀𝑀
Penetration (mm) Load (Kg) Stress (Mpa)
0.64 8.5 0.043
1.27 11.5 0.058
1.91 15 0.076
2.54 19.5 0.099
3.18 24 0.122
3.81 29.5 0.149
4.45 35.5 0.180
5.08 41 0.208
7.62 75 0.380
10.16 98.5 0.499
12.7 141 0.714

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CBR
0.800
0.714
0.700

0.600
0.499
0.500
0.380
0.400

0.300
0.149
0.200 0.058
0.122
0.208
0.076 0.180
0.100 0.043
0.099
0.000
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

56 Blows

Stress for 2.5mm Penration =0. 099 Mpa

Stress for 5mm Penration =0.2Mpa
Stress for 2.5mm Penration
%CBR 2.5 = ∗ 100
Stander stress at 2.5mm
0.099
%CBR 2.5 = ∗ 100 = 1.435
6.9
Stress for 5mm Penration
%CBR 5 = ∗ 100
Stander stress at 5mm
0.2
%CBR 5 = ∗ 100 = 1.942
10.3
∴ 𝐶𝐶ℎ𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜 𝐶𝐶𝐶𝐶𝐶𝐶 = 1.942
No. of Blows CBR ᵞ𝒅𝒅𝒅𝒅𝒅𝒅
10 1.5534 1.933
25 7.476 1.95
56 1.942 2.1585

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7.476
CBR
8

3
1.942
2 1.5534

0
1.9 1.95 2 2.05 2.1 2.15 2.2

CBR

Discussion

1. The California bearing ratio (CBR) is a penetration test for evaluation of the
mechanical strength of road subgrades and basecourses.
2. The CBR rating was developed for measuring the load-bearing capacity of
soils used for building roads. The CBR can also be used for measuring the
load-bearing capacity of unimproved airstrips or for soils under paved
airstrips. The harder the surface, the higher the CBR rating. A CBR of 3
equates to tilled farmland, a CBR of 4.75 equates to turf or moist clay, while
moist sand may have a CBR of 10. High quality crushed rock has a CBR
over 80. The standard material for this test is crushed California limestone
which has a value of 100.
3. The CBR in spite of its limited accuracy still remains the most generally
accepted method of determining subgrade strength, and as such this
information, along with information on traffic flows and traffic growth is
used to design road pavements.
4. The results obtained by these tests are used with the empirical curves to
determine the thickness of pavement and its component layers.
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In the case of 56 blows CBR test must return because CBR 0.1˶ smaller
then CBR 0.2˶ It is possible that the bonds between soil particles may be broken
due to the large number of strikes.

The following table shows some values of the (CBR) tolerance ratio:

AASHTO USC common Classification CBR endurance

system system Uses of materials ratio

Very weak
A5 ,A6,A7 OH,CH,MH,OL Earth base 0-3
A4 , A5
OH,CH,MH,OL Earth base Poor 3–7
,A6,A7
Under the
A2 , A4
OH,CH,MH,OL foundation Acceptable 7 – 20
,A6,A7
A1b , A2 – Base or
GM ,GC,SW
5, Good 20-50
,SM ,SP,GP sub-base
A3,A2-6
A1a,A2- Excellent
GW ,GM Base More than 50
4,A3
table shows some values of the (CBR) tolerance ratio

The standard values shown in the following table are used to calculate the
tolerance:
penetration Standard weight unit
(mm) (Mpa)
2.5 6.9
5.00 10.3
7.5 13.00
10 16.00

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