1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME
30
INFLUENCE OF SUBGRADE CONDITION ON RUTTING IN
FLEXIBLE PAVEMENTS- AN EXPERIMENTAL INVESTIGATION
Dr. K.V.Krishna Reddy
Professor & Principal, Chilkur Balaji Institute of Technology, Hyderabad-75, AP, India
ABSTRACT
In the present study, an attempt is made to investigate the influence of subgrade
condition on the rutting phenomena in flexible pavements. Flexible pavement section is
formed in a steel box section with a standard pavement section over a clayey subgrade. The
subgrade condition is varied by varying the CBR of the same by additives. Conventional and
strengthened surface courses were considered to check the influence of strengthened surface
courses in lowering the rut depth. The results indicated that the rutting phenomenon is
initiated in the subgrade itself and surface strengthening alone has low influence on limiting
rut formation.
Key Words: Rutting, Subgrade stabilization, Clay subgrades, CBR
1. INTRODUCTION
In recent years, Highways have experienced an increase in the severity and extent of
permanent deformation (rutting) in bituminous pavements. Rutting reflects not only the
structural condition of the pavement but also the functional condition and hence life cycle
costs. Need was recognized as to find which layer of the pavement needs attention to limit the
permanent deformation. Literature indicated that rutting could be ascribed to shear
deformation within the asphalt layer (primary rutting) or subgrade deformation (secondary
rutting). This paper investigates the influence of subgrade strength and surface modification
on rutting.
INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND
TECHNOLOGY (IJCIET)
ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
Volume 4, Issue 3, May - June (2013), pp. 30-37
© IAEME: www.iaeme.com/ijciet.asp
Journal Impact Factor (2013): 5.3277 (Calculated by GISI)
www.jifactor.com
IJCIET
© IAEME

2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME
31
2. RESEARCH METHODOLOGY
2.1 Subgrade strength variation
Laboratory experimentation is done to determine the optimum additives content for
stabilizing the clayey subgrade with pond ash-lime, sand and gravel to obtain subgrade
strength variation.
2.2 Surface course strengthening
80/100-penetration grade bitumen is considered for experimentation and aggregates
confirming midpoint gradation of grade II specifications as per MORTH specification have
been used. Hydrated lime was used to improve the strength of the bituminous concrete to be
used in the surface course.
2.3 Laboratory pavement setup
Laboratory based pavement sections with conventional materials and that with
different subgrades and modified surface course is prepared in a prefabricated box type
arrangement made of mild steel of size 40cm X 30 cm X 30 cm. Eight Laboratory based
multi layer sample pavement sections were formed, four of them namely pavement section
with clay subgrade and conventional surface course, pavement section with sand stabilized
subgrade and conventional surface, pavement section with gravel stabilized subgrade and
conventional surface and that with pond ash+lime stabilized subgrade and conventional
surface were formed. Another four pavement sections were formed a with the above
subgrades and lime modified surface course. All of them were soaked for 96 hours by passing
water continuously through the water inlet and draining the same through the water outlet
drainage pipes.
3 DATA ANALYSIS
3.1 Material Properties
Clay soil of highly expansive nature has been used as subgrade material. The liquid
limit and plasticity index were 79.3 and 47.84 respectively with a soaked CBR of 2.65.
Pondash+ lime , gravel and sand were used as additives to vary the strength of the subgrade
layer. The optimum additives content is evaluated by a series of laboratory tests. The
stabilized soil properties are depicted in Table 1 along with the basic soil properties used for
modification.
Aggregates corresponding to grade II specifications for base course materials
(MORTH) have been used in formation of water bound macadam (WBM). Gravel screenings
were used to fill the voids and the properties are as depicted in Table 2. Bitumen of 80/100-
penetration grade with grade II aggregates for bituminous concrete mix (MORTH) was used
in the formation of the surface course. Hydrated lime was used as modifier to strengthen the
bituminous concrete surface layer. The properties of the bituminous concrete along with lime
modified material are as in Table 3.

3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME
32
Table 1 Properties of clay and gravel used in laboratory sample pavement preparation
S.
N
o.
Property Clay Gravel
Clay +
25%PA +
5%lime
Clay+ 30%
gravel
Clay +
25% Sand
1 Grain Size
Distribution
Gravel (%)
Sand (%)
Silt size (%)
Clay size (%)
-
1.2
31.4
67.4
6
80
9.6
4.4
- - -
2 Atterberg Limits
Liquid Limit (%)
Plastic Limit (%)
Plasticity Index
Shrinkage Limit (%)
79.3
31.46
47.84
12.20
35
18.1
16.9
14.0
56.50
44.30
12.20
39.80
79.3
31.46
47.84
12.20
79.3
31.46
47.84
12.20
3 Compaction
properties
Optimum moisture
content (%)
Maximum Dry
Density (g/cc)
17.10
1.683
11.7
1.95
17.50
1.660
15.00
1.767
15.62
1.758
4 Soaked CBR (%) 2.65 11.4 16.6 5.18 4.22
5 Free swell index (%) - - 30
6 Swell potential (%) 1.20
7 UCC kN/m2
310 (7D)
Table 2 Properties of aggregate used for WBM of laboratory sample pavement
Property Value Property Value
Crushing value 18% Specific gravity 2.79(CA)/2.76(FA)
Impact value 14% Water absorption 0.8%
Abrasion value 22%
Table 3 Properties of bituminous concrete used for surface course of laboratory multi
layered sample pavement section
S.
No
Mix / Property Conventional
Lime
modified
1 Optimum Bitumen content
/lime content
4.3%
2.80%
2 MSV (Kg) 1300 2650
3 Air voids (%) 3.875 4.05
4 Flow value (mm) 2.375 3.5
5 Bulk density (g/cc) 2.520 2.446

4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME
33
3.2 Laboratory based multi layer sample pavement section
The thickness of the pavement layers have been designed to ensure that the stresses
reach the subgrade level. It was proposed to form the multi layer sample pavement section
with the 40mm thick bituminous concrete, 100mm thick WBM layer and 75 mm thick
subbase. The subbase was formed of 25mm thick well-graded sand overlain by 50mm of
gravel layer to facilitate free drainage of water during soaking. Figure 1 represent the
laboratory based pavement section. Figure 2 depict the laboratory conventional pavement and
the testing of the same
4 RESULTS
Hamburg wheel tracking device (Germany) was used to evaluate the rut depth. These
laboratory based pavement sections were subjected to wheel tracking on the wheel-tracking
device under a contact pressure of 5.6 kg/cm2
for a set of 1,10,000 revolutions.
GRAVEL SUBBASE
Fig 1(b) Cross section of modified multi
layer pavement section
Drainage
185mm
25 mm
100 mm
50 mm
40 mm
W B MACADAM
MODIFIED BITU CONC
WELL-GRADED SAND
STABILIZED SUBGRADE
W B MACADAM
WELL-GRADED SAND
GRAVEL SUBBASE
BITUMINOUS CONCRETE
CLAY SUBGRADE Drainage
Fig 1(a) Cross section of conventional
multi layer pavement section
Fig 2 (b) Photograph showing
wheel tracking of the laboratory
based pavement
Fig 2 (a) Photograph showing
laboratory based multilayer pavement

5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME
34
The wheel tracking test results in terms of rut depth for all pavement sections are noted down
for every 1000 revolutions. The rut depth at the end of 110000 revolutions is as presented in
Table 4. The results are plotted in terms of rut depth to number of wheel load repetitions as
depicted in Fig.3 for the conventional surfaced pavement sections and Fig.4 represent the rut
depth to number of wheel load repetitions for the lime modified surface pavement sections.
Table 4 Rut depth for pavement sections at the end of one lakh revolutions
S.No Pavement section
Rut depth
(mm)
1 Clay subgrade with conventional surface 1.91
2 PA+Lime stabilized subgrade with conventional surface 1.15
3 Gravel stabilized subgrade with conventional surface 1.40
4 Sand stabilized subgrade with conventional surface 1.51
5 Clay subgrade with lime modified surface 1.62
6
PA+Lime stabilized subgrade with Lime modified
surface
0.86
7
Gravel stabilized subgrade with lime modified
bituminous surface
1.09
8
Sand stabilized subgrade with lime modified bituminous
surface
1.21
Fig3. Rutdepth vs no. of wheel load repetions for pavement sections with conventional
surfaces
0.00 40000.00 80000.00 120000.00
No. of wheel load repetitions
0.00
400.00
800.00
1200.00
1600.00
2000.00
Rutdepthin0.01mm
1 clay subgrade + conventional surface Y = 0.0176931 * X + 57.9239 0.998302
Sno. Pavement Model selected Fit R Sq value
2 Sand stabilized subgrade + conventional surface Y = 0.0135704 * X + 38.7609 0.998868
3 Gravel stabilized subgrade + conventional surface Y = 0.0130083 * X + -17.2826 0.998938
4 PA + lime stabilized subgrade + conventional surface Y = 0.0109846 * X + -40.2391 0.998302
1
2
3
4

6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME
35
0.00 40000.00 80000.00 120000.00
No. of wheel load repetitions
0.00
400.00
800.00
1200.00
1600.00
2000.00
Rutdepthin0.01mm
1
2
3
4
Sno. Pavement Model selected Fit R Sq value
1 clay subgrade + lime modif surface Y = 0.0082419 * X + -30.4783 0.998233
2 Sand stabilized subgrade + lime modif surface Y = 0.0108273 * X + 33.1957 0.998841
3 Gravel stabilized subgrade + lime modif surface Y = 0.0101453 * X + -13.3804 0.998944
4 PA + lime stabilized subgrade + lime modif surface Y = 0.0082419 * X + -30.4783 0.998233
Fig4. Rutdepth vs no. of wheel load repetions for pavement sections with lime modified
surfaces
5 ACKNOWLEDGEMENT
At the outset the author would thank the Head, CED, Vasavi college of Engineering,
SE R&B Department and Head CED & TE Division and other professors at NIT Warangal
for their valuable guidance and encouragement during experimentation.
6 CONCLUSION
1. Rut depth resulted in the conventional pavement section under test conditions is more
by 66%,36% and 26.5% as compared to that resulted in conventional surface on
stabilized subgrade with pond ash-lime ,gravel and sand respectively clearly
highlighting the involvement of subgrade in rutting phenomena.
2. Rut depth resulted in the conventional pavement section under test conditions is more
by 122%, 75% and 47% as compared to that resulted in lime modified surface surface
on stabilized subgrade with pond ash-lime, gravel and sand stabilized subgrade
respectively. This highlights that though surface modification result in taking more
wheel load repetitions, subgrade modification results in achieving better rut control.
3. Rut depth resulted in the conventional pavement section under test conditions is more
by 18% as compared to the conventional subgrade with lime modified surface
showing that the improvement by modifying surface is less than that achieved by
improving the subgrade alone (66%).
4. Effective pavement performance is to understand the cause of rutting. Sound
judgment should be used to determine which part of the existing pavement structure is
weak and total reconstruction of the pavement or full depth reclamation should be
considered rather than just improving the surface if the subgrades are poor.

7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME
36
REFERENCES
1. Carl W. Lubold, Jr. (2001), “Are u in a Rut?”, Pro. Moving forward, The Pennsylvania
Local Road Program, Pennsylvania, Vol. 19, No.2, pp4-5.
2. Chang, D. J. J., Ho, N.H., Chang, H.Y., and Yeh, H.S. (1999), “Laboratory and Case
Study for Geogrid Reinforced Flexible Pavement Overlay”, TRR-1687, TRB, pp 125-
130.
3. Chaturvedi, A.C. (1977), “Expansive Soil in India with special reference to U.P.”, Proc.
of First National Symposium on Expansive Soils, HBTI- Kanpur, India, pp 2-1 to 2-5.
4. Chu, T.Y. (1955), “Soil Stabilisation with Lime Fly Ash mixture, Preliminary studies
with Silty and Clayey Soils”, HRB, No.108, p.102.
5. Collins, R. J., and Ciesielski, S. K. (1992), “Highway Construction use of wastes and
By-products” Utilization of Waste Materials in Civil Engineering Construction,
Published by ASCE, New York, pp.140-152
6. David, W., John, R., and Robert, H. (2003), “The Shell Bitumen Handbook”, Thomas
Telford ltd.
7. Diamond, S., and Kinter, E.B. (1965), “Mechanism of Soil-Lime Stabilisation- An
Interpretive Review” HRR, No.92, pp. 83-96.
8. Edil, T.B., Benson, C.H., Bin-Shafique, M.S., Tanyu, B.F., Kim, W.H., Senol. (2002),
“A Field Evaluation of Construction Alternatives for Roadways over Soft Subgrade”,
TRR-1786, TRB, pp 36-48.
9. Heckel, G. (2001), “Alternative Materials for Subgrade Modification”, Rep. No. IL-
PRR-138, Illinois Department of Transportation.
10. Hopkins, T.C., Beckham, T.L., Sun, L., Ni, B., and Butcher, B. (2002), “Long-Term
Benefits of Stabilizing Soil Subgrades” Rep. No. KTC-02-19/SPR-196-99-1F,
Kentucky Transportation Centre, University of Kentucky.
11. Huang, S.C., Petersen, J.C., Robertson, R.E., and Branthaver, J.F. (2002), “Effect of
Hydrated Lime on Long-Term Oxidative Aging Characteristics of Asphalt”, TRR-1810,
TRB, pp 17-24.
12. IRC 37 - 2001: Guidelines for Design of Flexible Pavements.
13. IRC : SP : 53 - 2002: Guidelines on Use of Polymer and Rubber Modified Bitumen in
Road Construction.
14. IS 2720 (part 16) - 1979, “Methods of Test for Soils; Laboratory Determination of
CBR”, Bureau of Indian Standards, New Delhi.
15. Kavussi, A., Hicks, R.G. (1997), “Properties of Bituminous Mixtures Containing
Different Fillers”, Journal of the Association of Asphalt Paving Technologists, Vol. 66,
pp 153-186.
16. Lesueur, D., and Little, D.N. (1999), “Effect of Hydrated Lime on Rheology, Fracture
and Aging of Bitumen” TRR-1661, TRB, pp 93-105.
17. Mohammad, L.N., Abadie, C., Gokmen, R., and Puppala, A.J. (2000), “Mechanistic
Evaluation of Hydrated Lime in Hot-Mix Asphalt Mixtures” TRR-1723, TRB, pp 26-
36.
18. Natarajan, T.K., and Shanmukha Rao, E. (1979), “Practical Lessons on Road
Construction in Black Cotton Soil Areas”, Road Research Papers, Rep.No.155, CRRI,
India.
19. Nayak, N.V., and Christensen, R.W. (1971), “Swelling Characteristics of Compacted
Expansive Soils”, Clay and Clay Minerals, Vol. 19, pp 251-261.

8. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 3, May - June (2013), © IAEME
37
20. Ramana Sastry, M.V.B., (1989), “Strengthening Subgrades of Roads in Deltaic Areas of
Andhra Pradesh”, Proc. Indian Geotechnical Conference, Visakhapatnam, Vol. 1,
pp 181-184.
21. Saxena, R.K. (1991), “Can Failures be Minimized and Pavement Performance
Improved by adequately Designing and Constructing Road Subgrades”, Journal of
Indian Roads Congress, Vol. 52, No.2, pp 263-317.
22. Sebaaly, P.E.; McCann, M., Hitti, E., and Epps. (2001), “Performance of Lime in Hot
Mix Asphalt Pavements”, Rep. No. RDT01-009, University of Nevada.
23. Thomas, Z. (2002), “Engineering Properties of Soil- Fly Ash Subgrade Mixtures”, Proc.
Transportation Scholars Conference, Iowa State University.
24. Dr. K.V.Krishna Reddy, “Rutting Resistance of Filler Modified Bituminous Concrete
Surfaces”, International Journal of Civil Engineering & Technology (IJCIET), Volume
4, Issue 2, 2013, pp. 250 - 257, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.
25. 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.
26. Ravin M. Tailor, Prof. M. D. Desai and Prof. N. C. Shah, “Performance Observations
for Geotextile Reinforced Flexible Pavement on Swelling Subgrade: A Case of Surat,
India”, International Journal of Civil Engineering & Technology (IJCIET), Volume 3,
Issue 2, 2012, pp. 347 - 352, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.