20120130406011

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 6, September – October (2013), © IAEME
98
SHEAR STRENGTH CHARACTERISTICS OF A ROCKFILL MATERIAL
Brijesh Kumar1
, Nitish Puri2
, Saurabh Jaglan3
1
(Associate Professor, Department of Civil Engineering, SIET, Ambala, Haryana, India)
2
(Research Scholar, Department of Civil Engineering, NIT, Kurukshetra, Haryana, India)
3
(Assistant Professor, Department of Civil Engineering, GGGI, Ambala, Haryana, India)
ABSTRACT
In last five decades, direct shear test has emerged out as an effective method for determining
shear strength of soils and various other materials, because of its simplicity and reliable results. It is a
common practice to perform direct shear box tests on granular soils to determine the shear strength
for engineering purposes. However, same shear box cannot be used for all types of materials, as
particle size of rockfill varies from very small (less than equal to 4.75 mm) to very large (more than
4.75 mm). Hence larger particles are tested in moderate or large shear boxes. The shear strength is
required whenever a structure’s stability and serviceability is dependent upon shearing resistance of
soils. The shear strength is required for various engineering purposes such as determination of
stability of slopes or cuts, bearing capacity calculations for foundations and for the calculation of
earth pressure exerted by a soil on a retaining structure. A moderate sized direct shear box test was
used to determine the shear strength characteristics of Beas river rockfill of varying sizes. Shear
stress, void ratio, angle of shearing resistance (Φ) and shear strength over the range of normal
pressure varying from 1.0 to 2.0 kg/cm2
for various grain sizes of rockfill were determined. It has
been observed that the angle of shearing resistance increases with decrease in particle size at a
particular void ratio. However, a general decrease in shear stress is observed with increasing values
of grain size.
Keywords: Direct shear test, Grain size, Shear box, Shearing resistance, Void ratio.
1. INTRODUCTION
Direct shear test is a standard method for determining shear strength characteristics of soils of
almost all sizes. It is possible to test soil samples with large grain sizes (>4.75 mm), which is an
important advantage of this test. Methods for carrying out direct shear tests for geotechnical
engineering purposes are well established in practice [14]. Shear strength parameters are used in
design of earthen dams and embankments, calculation of bearing capacity of soil-foundation
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN
ENGINEERING AND TECHNOLOGY (IJARET)
ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
Volume 4, Issue 6, September – October 2013, pp. 98-109
© IAEME: www.iaeme.com/ijaret.asp
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99
systems, estimation of earth pressure behind the retaining walls and to check the stability of natural
slopes, cuts and fills. Shear strength of soil has its maximum resistance to shearing stress at failure
on the failure envelope. Shear strength is composed of two parameters, firstly, angle internal friction
(Φ) which is the resistance due to friction between individual particles at their contact points and
interlocking of particles and second, is cohesion (C) which is resistance due to inter-particle forces
which tend to hold the particles together in a soil mass. The second parameter is almost negligible
when coarse grained particles are concerned [11].
The relation of these two parameters (C, Φ) with shear strength (τ) of soil has been given by
equation 1 proposed by Coulomb:
τ = C + σ tanΦ
For coarser materials the cohesion between particles is almost zero so equation 1 will change
to equation 2 shown below:
τ = σ tanΦ
A few decades back, direct shear tests were only carried out for finer particles (< 4.75 mm)
due to unavailability of bigger shear boxes. But in the present scenario, with advancement in
technology and vision things have become possible. Now a day’s larger shear boxes are available
and can be incorporated in determining shear characteristics of larger grain sizes of specimens. Also
engineering properties of coarser material have to be investigated as these materials are being used in
railway tracks, earth dams, earth canal embankments, earth canal lining and pavement construction.
It is a common practice to use gravelly soils if locally available because of their high stability and
strength characteristics. A series of direct shear tests was conducted in order to determine shear
strength characteristics of rockfill with respect to variation in these two parameters:
1. Void ratio
2. Average particle size
These parameters are of great importance to highway engineers and geotechnical engineers
involved in construction of various earth and earth retaining structures.
2. MATERIALS & METHODOLOGY
2.1 Rockfill material
The rounded, sub angular, angular crushed and coarse grained rockfill from the banks of Beas
River were used as the base materials in the tests. Rockfill was collected from Bharat Stone Crushing
Co, Stone Crushers and Stone Metal Suppliers, Dalhousie Road, Pathankot-145001. They are
available on the basis of size and shape. The material is classified as GW (well graded gravels) and
grayish in colour as per the specifications of IS codes. The specific gravity of Beas river rockfill was
calculated and found to be 2.67. The absorption value for the rockfill has been observed as 1.84%.
Brazilian test was performed in order to determine tensile strength of rockfill, it was found to be
16.77 kg/cm2
. This ensures that specimen is medium strong and can resist normal wear and tear.
Various types of rockfill materials collected are tabulated below in Table1.

100
Table1. Particle sizes of various rockfill
S. No. Type of Rockfill Size (mm)
1. Rounded Beas River Rockfill 10 – 12.5
2. Sub angular crushed Beas Rockfill
6.3 - 10
3. Angular Crushed Beas Rockfill
(a) 4.75 - 6.3
(b) 2.36 - 6.3
4. Coarse Grained Beas Rockfill 1 - 2.36
2.2. Test Apparatus
Direct Box shear tests have been performed on rounded and crushed rockfill of different size.
The natural river rockfill were rounded or sub rounded whereas the crushed rockfill were angular or
sub angular in shape. The shear box used for the testing had the internal dimensions 30 x 30 x 12 cm,
made of thick steel plates to hold the sample. The moderate sized shear box is ideal for testing
geosynthetics and also soil and other materials that contain large particles of up to 20 mm. The
sample is consolidated by the application of the vertical load. The horizontal displacement is driven
by a high resolution stepper motor. The machine is entirely managed manually and the technical
assistant reads the processes of force, axial pressure and displacements, manages the motor, the
vertical hydraulic loading system. Using a large sample is possible to gain a more representative
indication of shear strength. Furthermore, the large shear box can be used to obtain the angle of
friction between many materials. Particular applications include the construction of earth dams and
other embankment work. The machine includes 100 kN load cell, three dial gauges, mounting
brackets and shear box.
Fig.1. Direct shear test apparatus with moderate sized shear box
2.3 Methodology
The test is carried out on a soil sample confined in a metal box of square cross-section which
is split horizontally at mid-height. A small clearance is maintained between the two halves of the
box. The soil is sheared along a predetermined plane by moving the top half of the box relative to the
bottom half. A typical shear box is shown below:

101
Fig.2. Shear Box Apparatus, Source: Engineering Soil Testing Manual
By Shamsher Prakash and P.K Jain [10]
If the soil sample is fully or partially saturated, perforated metal plates and porous stones are
placed below and above the sample to allow free drainage. If the sample is dry, solid metal plates are
used. A load normal to the plane of shearing can be applied to the soil sample through the lid of the
box. Tests on sands and rockfill can be performed quickly, and are usually performed dry as it is
found that water does not significantly affect the drained strength. For clays, the rate of shearing
must be chosen to prevent excess pore pressures building up. As a vertical normal load is applied to
the sample, shear stress is gradually applied horizontally, by causing the two halves of the box to
move relative to each other. The shear load is measured together with the corresponding shear
displacement. The change of thickness of the sample is also measured. A number of samples of the
soil are tested each under different vertical loads and the value of shear stress at failure is plotted
against the normal stress for each test. Provided there is no excess pore water pressure in the soil, the
total and effective stresses will be identical. From the stresses at failure, the failure envelope can be
obtained. The above explained methodology is as per the specifications of ASTM: D3080-98 and IS.
2720 (Part XIII), (1986) [1][3]. The main advantage of this test is that it is easy to test sands and
rockfill. Large samples can be tested in large shear boxes, as small samples can give misleading
results due to imperfections such as fractures and fissures, or may not be truly representative. Also
samples can be sheared along predetermined planes, when the shear strength along fissures or other
selected planes are needed [15].
There are some disadvantages as well and the major demerit is that the failure plane is always
horizontal in the test, and this may not be the weakest plane in the sample. Failure of the soil occurs
progressively from the edges towards the centre of the sample. Also, there is no provision for
measuring pore water pressure in the shear box and so it is not possible to determine effective
stresses from undrained tests. Moreover, the shear box apparatus cannot give reliable undrained
strengths because it is impossible to prevent localised drainage away from the shear plane [13].
3. EXPERIMENTAL INVESTIGATIONS
A series of tests were conducted on rockfill and the samples were subjected to normal
stresses ranging from about 1.0 Kg/cm2
to 2.0 Kg/cm2
. The shear strength values corresponding to
different normal loads for Beas river rockfill are presented in Table.2 below.

102
Table2. Strength characteristics of various rockfill
Type of Particles
Particle size
(in mm)
Shear force at
Failure (Kg)
Normal
stress
(Kg/cm2
)
Shear stress
at failure
(Kg/cm2
)
Rounded 10 – 12.5 882 1.0 0.98
rockfill 1285 1.5 1.428
1836 2.0 2.04
Sub Angular 6.3 - 10 975 1.0 1.083
Crushed 1489 1.5 1.654
Gravel 1840 2.0 2.044
Angular 4.75-6.3 1033 1.0 1.148
crushed 1515 1.5 1.683
gravel 1951 2.0 2.168
Angular 2.3 - 6.3 1080 1.0 1.2
crushed 1552 1.5 1.72
gravel 2003 2.0 2.226
Coarse 1 – 2.36 1314 1.0 1.46
grained 1575 1.5 1.750
gravel 2002 2.0 2.244
The variation of shear stress with normal stress is plotted for various rockfill materials and the results
are shown in Fig.3 to Fig.7.
Fig.3. Variation of shear stress vs. normal stress for rounded river rockfill of size range 10 –
12.5 mm
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2 2.5
Shearstress(Kg/cm2)
Normal stress (Kg/cm2)

103
Fig.4. Variation of shear stress vs. normal stress for sub angular crushed river rockfill of size
range 6.3 – 10 mm
Fig.5. Variation of shear stress vs. normal stress for angular crushed river rockfill of size
range 4.75 - 6.3 mm
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2 2.5
Shearstress(Kg/cm2)
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2 2.5
Shearstress(kg/cm2)

104
Fig.6. Variation of shear stress vs. normal stress for angular crushed river rockfill of size
range 2.36 - 6.3 mm
Fig.7. Variation of shear stress vs. normal stress for coarse grained river rockfill of size range 1
- 2.36 mm
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2 2.5
ShearSress(Kg/cm2)
Normal Sress (Kg/cm2)
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2 2.5
ShearSress(Kg/cm2)
Normal Sress (Kg/cm2)

105
The Angle of shearing resistance (ф) corresponding to void ratio was calculated at failure
shear stress for Beas river rockfill and are reported in Fig.8 to Fig.12.
Fig.8. Variation of Angle of Shearing Resistance vs. Void Ratio for rounded river rockfill of
size range 10 – 12.5 mm
Fig.9. Variation of Angle of Shearing Resistance vs. Void Ratio for sub angular crushed river
rockfill of size range 6.3 – 10 mm
37.5
38
38.5
39
39.5
40
40.5
41
41.5
42
42.5
0.5 0.6 0.725 0.825
AngleofShearingResistance(ф)
Void Ratio (e)
1.041
(Normal
stress
Kg/cm2)
1.566
2.081
39.5
40
40.5
41
41.5
42
42.5
43
43.5
44
44.5
0.5 0.6 0.725 0.825
Void Ratio
1.041 (Normal
stress Kg/cm2)
1.566
2.081

106
Fig.10. Variation of Angle of Shearing Resistance vs. Void Ratio for Angular crushed river
rockfill of size range 4.75 – 6.3 mm
Fig.11. Variation of Angle of Shearing Resistance vs. Void Ratio for Angular crushed river
rockfill of size range 2.36 – 6.3 mm
42
42.5
43
43.5
44
44.5
45
45.5
46
0 0.2 0.4 0.6 0.8 1
Void Ratio
1.041
(Normal
stress
Kg/cm2)
1.566
2.081
43.5
44
44.5
45
45.5
46
46.5
47
0 0.2 0.4 0.6 0.8 1
Void Ratio
1.041 (Normal
stress Kg/cm2)
1.566
2.081

107
Fig.12. Variation of Angle of Shearing Resistance vs. Void Ratio for Coarse Grained River
rockfill of size range 1 - 2.36 mm
4. RESULTS AND DISCUSSIONS
The shear strength of rockfill material depends on shearing resistance offered by its grains
due to interparticle friction and locking. It has been observed that the angle of shearing resistance (Φ)
increases with decrease in size of shear box. However, size of shear box was not a deciding
parameter in our study. But authors suggest this criterion for further research. It also depends on the
particle size, gradation of material and the size of shear box used. Following results have been
observed in context with:
4.1. Angle of shearing resistance
It has been observed that the angle of shearing resistance increases with decrease in particle
size at a particular void ratio. It has been observed that the angle of internal friction reduced from
42.5˚ to 48.5˚ with decrease in particle size from 12.5 mm to 1 mm for Beas river rockfill. However,
the angle of internal friction decreases with increase in normal stress at a particular void ratio. Also
Angle of shearing resistance decreases with increase in void ratio at a particular normal stress. These
results are clearly verified in Fig.8 to Fig.12.
4.2 Shear stress
From Fig.3 to Fig.7 it can be observed that shear stress increases with increase in normal
stress for a particular grain size. However, a general decrease in shear stress is observed with
increasing values of grain size. All the results of this study are in accordance with many other
investigators [2][4-9][12].
44.5
45
45.5
46
46.5
47
47.5
0 0.2 0.4 0.6 0.8 1
Void Ratio
1.041
(Normal
stress
Kg/cm2)
1.566
2.081

108
CONCLUSIONS
Direct shear tests were conducted on rockfill obtained from Beas River, Pathankot over the
range of normal stress from 1.0 to 2.0 kg /cm2. The following conclusions have been drawn on the
basis of test results analyzed:
1. The angle of internal friction reduced from 48.5˚ to 42.5˚ with increasing particle sizes of
rockfill. Moreover, the current values of Φ were found suitable for designing rockfill dams
(as a slope of 1.4:1 or 1.3:1 can be obtained easily by using these gravels or rockfill).
2. Also an average shear strength 2.0 kg/cm2
has been observed, which is quite suitable if
gravels are to be used in sub-grade design and construction.
3. Also specific gravity of the rockfill material has been observed to be 2.67 while its absorption
limit and tensile strength values are 1.84% (must be less than 2%) and 16.77 kg/cm2
respectively. This assures the durability of our rockfill material.
ACKNOWLEDGEMENTS
Authors acknowledge the support provided by Department of Civil Engineering, Shivalik Institute of
Engineering and Technology (SIET), Ambala and Department of Civil Engineering, Galaxy Global
Group of Institutes (GGGI), Ambala.
REFERENCES
1. ASTM: D3080-98, “Standard Test Method for Direct Shear Test of Soils Under Consolidated
Drained Conditions” , American Society for Testing and Materials.
2. Bishop, A.W., (1948) , “A Large Shear Box for testing Sand and Rockfill” , Proceedings of
Second International conference on Soil Mechanics and Foundation Engineer, Vol.1 , pp 207-
211 .
3. IS. 2720 (Part XIII), (1986),” Indian Standard Methods of Test for Soils: Direct Shear Test”,
Bureau of Indian Standards.
4. Fukoka, M., (1965), “Testing if Gravelly Soil with Large Scale Apparatus”, Proceedings of
the IVth
International conference on Soil Mechanics and Foundation Engineering, Vol.1.
London, pp 153-155.
5. Hansen, B., (1961), “Shear Box Tests on Sand”, Proceedings of Vth
International Conference
on Soil Mechanics and Foundation Engineering, Paris 1, pp 127-131.
6. Kezdi, A., (1974), “Handbook of Soil Mechanics”, Elsevier Scientific Publishing Company,
Budapest.
7. Mariachi, N.D., Chan, C.K., and Seed H.B., and Duncan, J.M., (1960) , “Strength and
Deformation Characteristics of Rock fill Materials”, Report No. TE-969-5, State of California
Department of Water Resources, University of California, Berkeley.
8. Marshal, R.J., (1969), “Large scale testing of Rock fill Materials” Journals of Soil Mechanics
and Foundation Division, ASCE , Vol.93, No. SM2, pp 27-43.
9. Patel, P.J, Patel, Mukesh A., Patel, H.S, (2013) “Effect Of Coarse Aggregate Characteristics
On Strength Properties Of High Performance Concrete Using Mineral And Chemical
Admixtures”, International Journal of Civil Engineering and Technology (IJCIET), Volume
4, Issue 2, March - April (2013).
10. Prakash, Shamsher and Jain, P.K, (1999), “Engineering Soil Testing”, Nem Chand & Bros,
Roorkee.
11. Ranjan, Gopal and Rao, A.S.R (2000), “Basics and Applied Soil Mechanics”, New Age
International (P) Ltd., New Delhi.

109
12. Sadasivan, S.K. and Rajee, V.S.,(1969), “Theory for Shear Strength of Granular Materials”
Journal of the Geotechnical Engg. Div., ASCE Proceedings, Vol. 103, No. GT8, pp 851-861.
13. Singh, Alam and Chowdhary, G.R. (1994), “Soil Engineering in Theory and Practice”,
Geotechnical Testing and Instrumentation, Vol. 2, CBS Publishers and Distributors, Delhi.
14. Nakao, Tomoyo and Fityus, Stephen (2009), “Direct Shear Testing of a Marginal Material
Using a Large Shear Box”, Geotechnical Testing Journal, Vol. 31, No. 5.
15. Website:- http://nptel.iitm.ac.in/
16. Nagendra Prasad.K, Sivaramulu Naidu.D, Harsha Vardhan Reddy. M and Chandra.B,
“Framework for Assessment of Shear Strength Parameters of Residual Tropical Soils”,
International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 2, 2013,
pp. 189 - 207, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.
17. Brijesh Kumar and Nitish Puri, “Stabilization of Weak Pavement Subgrades using Cement
Kiln Dust”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4,
Issue 1, 2013, pp. 26 - 37, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.

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