OPTIMUM DESIGN FOR HIGHWAY EMBANKMENT WITH STONE COLUMN

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 8, Issue 1, January 2017, pp. 863–872 Article ID: IJCIET_08_01_102
Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=1
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication Scopus Indexed
OPTIMUM DESIGN FOR HIGHWAY EMBANKMENT
WITH STONE COLUMN
Abdul-Hassan K. Al-Shukur
PhD., Professor, Department of Civil Engineering, College of Engineering,
University of Babylon, Babylon, Iraq
Huda Nihad Al-Khafajy
M.Sc. Postgraduate Student, Department of Civil Engineering, College of Engineering,
University of Babylon, Babylon, Iraq
ABSTRAT
In this paper discusses how to design the highway embankment with an optimum process to
get a minimum area of the highway embankment to reduce the cost of construction, and the
problems of soft clay soil in southern of Iraq when construction highway embankment as low
bearing capacity and excessive settlement and the way to treat it.At beginning a model of the
high way embankment without improving of soft clay soil for height of highway embankments
(H=2m and H=3m) was built to note the problems which will be faced when construction of
highway embankment in the future. When the height of embankment is (H=2m) the excessive
settlement appears but when the height of embankment is (H=3m) the low bearing capacity as
well as the excessive settlement will appear. To avoid these problems, the soft clay soil will be
improved by using stone columns and design the stone columns also with optimum process to
get minimum area of stone columns that can carry the applied load without any problem like
low bearing capacity or excessive settlement with lowest cost. When the stone columns are
used to improve the soft clay soil, it can note reduce in settlement by (99%) for height of
highway embankment (H=2m), and increase in bearing capacity to (15%) for height of
highway embankment (H=3m) for certain diameter as minimum increase can carry the load
applied on foundation. The highway embankment with stone column modeling with ANSYS
software program and this program very useful to help to find optimum design by optimization
tool, and use geo slope program to find slope stability for highway embankment by Bishop’s
method.
Key words: stone columns, highway embankment, soft clay, and diameter.
Cite this Article Abdul-Hassan K. Al-Shukur and Huda Nihad Al-Khafajy, Optimum Design
for Highway Embankment with Stone Column. International Journal of Civil Engineering and
Technology, 8(1), 2017, pp. 863–872.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=1

Optimum Design for Highway Embankment with Stone Column
1. INTRODUCTION
The purpose of optimization is to find the best possible solution among many potential solutions
satisfying the chosen criteria. Designers often base their designs on the minimum cost as an objective,
taking into account mainly the costs of the structure itself, safety, and serviceability.
An embankment is an artificial barrier that typically is used to hold back water or to support a
roadway, railway, or canal. The material use in embankment can be naturel like (sand, rock….etc.) or
manmade, in general any material can be use but non organic material. The highway embankment
consists of soil that is placed on the embankment foundation in order to raise the level of the roadway
to the correct grade and to provide adequate support for the layers of base and surface courses that
make up the roadway. Since the embankment foundation and embankment provide the basic support
of the entire roadway, it is very important that they be properly constructed in accordance with all
plans and specifications. Grades, slopes, density, and all other controls must be accurately monitored.
The highway embankment founded on soft clay soil. Soft clays represent a well-known category of
problematic soils which are generally encountered under the form of deposited layers in coastal areas.
Several problems are faced when dealing with the study of soft clays from field investigation, soil
characterization, behavior modeling, and stability of geotechnical structures up to ground
improvement solutions. Studying the behavior of soft clays especially requires a thorough
determination of their geotechnical parameters. In Iraq, the problems of this soil taken space from the
attention of geologists and civil engineers, because about 35% of the Iraqi clay soils (especially
southern Iraq) are weak[1,2]. So, necessity to improve soil properties for road building has resulted in
the use of various stabilizers. Ground improvement is normally understood as the modification of the
existing physical properties of the ground beneath a site to sufficient depth to enable effective,
economic, and safe permanent or temporary construction in practical timescales [3]. Typical objectives
would be one or a combination of the following:
1. Improve bearing capacity by increasing in shear strength or density.
2. Minimize total or differential settlements of buildings or structures by reduction in compressibility.
3. Minimize flow of ground water to prevent inundation or water damage by reduction in permeability
4. Prevention of liquefaction or reduction in lateral spreading beneath or near both new and existing
structures during earthquakes, employing densification, replacement with stronger materials, or deep
drainage.
5. Conversely, an improvement in deep drainage in order to assist preloading or surcharge techniques.
6. Controlled displacement of the ground in order to dispel previous differential settlements or ground
2. FORMULATION OF OPTIMIZATION PROCESS
2.1. The Objective Function
The objective function for embankment is based on minimum cost for this purpose the area of
embankment should be minimize. It can be formulated as follow:
Min. A = H*(b + H/m) +
Where:
H: embankment height (m)
b : top width of embankment (m)
m:slope of embankment
D: diameter of stone column (m)

Abdul-Hassan K. Al-Shukur and Huda Nihad Al-Khafajy
2.2. The Constraints
The objective function is minimized subject to a set of constraints. Some of these constraints can be
explicitly defined in terms of the design variables (i.e., side constraints), such as dimensions (m: must
be ≤ ½) [4]
,(0.5m ≤ D ≤ 1.2m) [5]
), while others are implicitly related to design variables.
2.2.1. Bearing Capacity
Qu = σv∗
∗
.
…… (Qu˃Qall)(1)
σv = σrLKpcol(2)
σrL= pp= γ*kp*z + 2*cu* (3)
Where :( σv) limiting axil stress in the column when it approaches shear failure due to bulging
,(σrL) limiting radial stress,(Kpcol)passive earth pressure ( Kp= tan2
(45+ ), (pp ) passive pressure,(γ)
effective unit weight of soil within the in influence zone,(z) average bulge depth (2 time the column
diameter ),(cu )cohesion of soft clay,(kp )passive pressure coefficient of soft
clay(kp=tan2
(45+ /2),where angle of friction of soft clay) and (1.5) factor of safety [5].
2.2.2. Slope Stability
F=∑
∑[{ + tan ′}
&'
(
)*+ , )*+ -.
/
] (4)
Where :(F) Factor of slope stability (for embankment must be ≥ 1.5), (W)weight of each slice, (cꞌ)
cohesion of soil, (b) width of each slice, and ( ꞌ) angle of friction [6].
2.2.3. Settlement
After construction the stone column and at the center of building the settlement for each layer i is
expressed as follows:
S=
12∗34
56∗7 89({: ;56)∗7<869}
(5)
Where: (ai) the replacement ratio for layer i (ai=
=
=>
,A: total area within the unit cell ,Ac: area of
stone column),(Ecol)young modulus of stone column, (Esoil) young modulus of soft clay, (σt)average of
vertical stress exerted by building and (hi) layer thickness.
The total settlement (∑S) should remain below the values set by the operation condition.
2.2.4. Maximum Allowable Stress for Stone Column
It is need to determine the vertical stress-rupture point (qr) for an isolated column at first to calculate
the maximum allowable stress, based on characteristic of column and the soil after treatment and
according to possible mode of failure[7].
Bulging failure
qre = σrL*kpcol (6)
• (σrL) calculate as equation (3) above
Punching effect shear failure
The vertical shear within the column is most intense at top and decreases as it moves down.
qrp = 9 ∗ @A + B>:2 ∗
DE
F
− H>) (7)
where :
γc: unit weight of stone column material

Lc:length of column
Rc: average radius of the column
• Vertical failure stress (qr) within the column equal to :
qr = min(qre , qrp , 1.6 Mpa).At the service limit state (SLS), the allowable vertical stress (qaSLS) within
the column is obtained by applying safety factor of 2 to the vertical failure stress (qr) :
• Value of stress within column at the layer i (σci) can be expressed as :
σci=
7 89∗34
56∗7 89( : ;56 ∗7<869%
(8)
• The stresses should remain below maximum allowable values (σci˂ qaSLS)
3. PLOT MODEL BY ANSYS
For design optimization model in ANSYS should be built the model to get optimum shape and
dimensions for embankment, this built include drawing shape define material, element used with
meshing for finite element process, boundary condition and load applied.
3.1. Drawing Model
It suggested symmetrical model, is drawn after defining the initial values of variable which draw the
initial shape of embankment and stone column and then hole model configuration as shown in
figure(1).
Figure 1 Model of Highway Embankment with Stone Column
3.2. Define Properties of Material
The properties of material used in optimum design of highway embankment with stone column as
shown in table below:
Table 1 Shown Properties of Material Used in Design
material Yong modulus(E)
(Mpa)
Poisson’s
ratio(ϒ)
Density (γ)
(KN/m2
)
Cohesion (cu)
(KN/m2
)
Embankment 80 0.3 20 5 30
Soft clay 2.4 0.4 17.7 15.8 11
Sand clay 50 0.3 18.3 5 25
subbase 400 0.35 22 ------ ---
asphalt 5000 0.35 23.5 ------ ---
Stone column 60 0.3 19 0 44

The properties of soft clay material were taken nearby Korek company Building Al-Hilla City.
Figure 2 Shown Korek Company Building Al-HillaCity[8]
3.3. Chose Element
PLANE 82 is used for 2-D modeling of solid structures.PLANE82 is a higher order version of the 2-D,
four-node element (PLANE42). It provides more accurate results for mixed (quadrilateral-triangular)
automatic meshes and can tolerate irregular shapes without as much loss of accuracy. The 8-node
elements have compatible displacement shapes and are well suited to model curved boundaries. The 8-
node element is defined by eight nodes having two degrees of freedom at each node: translations in the
nodal x and y directions. The element may be used as a plane element or as an ax symmetric element.
The element has plasticity, creep, swelling, stress stiffening, large deflection, and large strain
capabilities. Various printout options are also available.
Figure 3 Plane 82 Geometry
3.4. Boundary Condition
The foundation of embankment model is fixed at bottom and sides in which no translation permissible
in X and y directions as shown in figure (4).
Figure 4 Shown the Mesh and Boundary Condition

3.5. Applied Load
The surcharge load (traffic load) applied at the top of embankment model as pressure (uniform
distribution pressure) as shown in figure (5).
Figure 5 The Distribution of Load
4. RESULTS AND DISCUSSION
4.1. Verification of Optimization Process
In this section it will be made verification between optimum design process and ordinary design of
highway embankment and notes the different between two methods of design by shown the reduction
in variable design when use optimum process which lead to minimize the cost of constriction.
The following case study in Hampton, Virginia in interstate route 664 with interstate route 64
involved numerous highway embankment which designed by ordinary method and it will be designed
one of them by optimum method using ANSYS program.
Figure 6 General Location Plan

The table below shown properties of material and information about design of case study:
Table 2 Properties of Material
Input parameter Sample Unit Value
height H m 4
Surcharge qu kpa 11.5
Unit weight of highway embankment γe Kn/m3
20
Friction angle of highway embankment Φe …… 30
Unit weight of soft clay soil γc Kn/m3
13.3
Cohesive of soft clay soil Cu kpa 18
Friction angle of soft clay soil Φc …… 0
Young modulus of soft clay soil Eu kpa 2700
Unit weight of stone column γs Kn/m3
19.5
Friction angle of stone column Φs ……. 45
Spicing between columns S m 2.1
Young modulus of stone column Eu kpa 60*103
Length of stone column L m 7
For optimum purpose it will be get out limitation to get minimum area. When design the case
study above with optimum process by ANSYS program and comparison with ordinary design as
shown in the table below it can be noted the decreasing in diameter of stone column and increasing in
slope of highway embankment.
Table 3 Comparison Results Between Ordinary and Optimum Methods
Variable design Ordinary method Optimum method
m ½(V:H) 1/1.75(V:H)
D(m) 1.2 0.81
Area of embankment(m2
) 76 72
Volume of stone column(m3
) 8 3.6
The percentage of decreasing in diameter of stone column is (32.5%) and the percentage of
increasing in slope of highway embankment is (14.2%).From above equation it can noted the optimum
method is an effective method leads to optimum values of cost and safety factors compared with
Ordinary design.
4.2. Embankment without Improving Soil
At begging it was being shown the model of embankment without improving soil to know at any
factor of safety was failed as table (5.1).
Table 4 Initial and Infeasible Set for Model without Improving
* Initial Set
H
m
M
…….
Qu
Kn/m2
Qall
Kn/m2
Se
mm
Sp
mm
Ssec
mm
St
mm
Streq
mm
Fs
…..
A
m2
2 0.50 60 50.246 63.328 176.72 9 249.048˃ 50 4.475 30
3 0.50 60< 69.094 54.572 210.85 9 274.422˃ 50 2.33 51

In the table above which showed the initial set (initial value of design variable) and which factor
failed (cell in blue color), It can be notes in initial set the bearing capacity is less than the required
value and the total settlement is more than the required value (excessive settlement). In Infeasible set
the same problem because the soil is wake and cannot be carried the load without failed. At height of
embankment (H=2m) the bearing capacity of soft soil can carry the applied load but the problem still
with the excessive settlement, the settlement within the soil is very high. The reduction in settlementis
(80%)
That’s mean it needs (80%) reduction in settlement to reach for required settlement.
At height of embankment (H=3m) in addition to the problem of excessive settlement the average
of bearing capacity of soft clay is less than the allowable stress from embankment applied on soil as
shown in the table above that’s mean the soil cannot be able to carry the load applied on it. The
reduction in settlementis (81.8%), and the Increase in bearing capacity is (15.15%).That’s mean it
needs (15.15%) increasing in bearing capacity of soft clay to carry the applied load.
In this case its need to improve the soft clay to increase bearing capacity and reduce the excessive
settlement. In this thesis the stone columns will be used for this purpose as mentioned before.
4.3. Embankment with Improving Soil
Using stone columns to improve weak soil by increasing bearing capacity and decreasing the
excessive settlement, figure (7) shows the different in settlement between soil with and without
improvement for the same properties of embankment in table (5).
Figure 7 The Settlement With and Without Improving Soil
In figure above it can be noted the obvious decreasing in the settlement with improving soil of
certain diameter from stone columns for each height of embankment. The percentage in decreasing of
the settlement is (98.66%) (For height of embankment (H=3m))
The decreasing reaches (99%) for certain diameter, this decreasing in the settlement by stone
columns made soft clay within the acceptable limit.
without improving with improving
d=0.5 h=2 249.048 7.7469
d=0.55 h=3 274.422 7.9735
0
50
100
150
200
250
300
settlement(mm)
Infeasible set
H
m
M
…….
Qu
Kn/m2
Qall
Kn/m2
Se
mm
Sp
mm
Ssec
mm
St
mm
Streq
mm
Fs
…..
A
m2
*
2 0.43 60 50.246 63.615 177.05 9 249.665˃ 50 4.475 31.16
*
3 0.43 60< 69.094 54.730 211.25 9 274.98 ˃ 50 2.53 53.6

The improvement in bearing capacity with stone columns shown in figure (8) below, this figure
shows the different in bearing capacity between the soil with and without improvement for the same
properties of embankment in table (5).
Figure (8) the Bearing Capacity With and Without Improving Soil
In figure above it can be noted the improvement in bearing capacity when using stone columns, the
percentage of increasing in bearing capacity depends on diameter of stone column; with increasing the
diameter of stone columns, the improvement in bearing capacity increases for the same height of
embankment. For minimum area of embankment and stone columns using steeper slope for
embankment and minimum diameter of stone columns which achieve the recommendation of design.
The percentage of increasing in bearing capacity after improving soil for height of embankment
(H=2m) with minimum diameter which archive the recommendation of design is (3.14%).In table (5)
it can be noted that the height of embankment (H=2m) doesn’t need to improving in bearing capacity
as refer before but need to reduce the excessive settlement then the minimum diameter of stone
columns (D=0.5m) use to improve soft clay to reduce settlement within acceptable limit. The
percentage of increasing in bearing capacity after improving soft clay soil for height of embankment
(H=3m) is (18.04%). From table (5) and for height of embankment (H=3m) its need to improve soft
clay soil to increase bearing capacity and reduce excessive settlement as refer before, then (D=0.55m)
it’s the minimum diameter of stone columns use for improving soft clay to archive the
recommendation of design.
At height of embankment (H=3m) it can notes the dominate factor in design it is bearing capacity
for this reason its need to increasing diameter of stone columns from (0.5m for (H=2m) to 0.55m for
(H=3m)) to improve bearing capacity until the foundation can carry the load applied on it.
5. CONCLUSIONS
• The ANSYS APDL is efficient tool to simulate highway embankment foundation interaction problem
and optimization process.
• The individual-accumulative optimization technique used in this researcher gives reasonable procedure
to carry out the factor of safety individually.
• The soft clay soil in southern of Iraq cannot carry the applied load and it is failed by bearing capacity
and excessive settlement for that it is necessary to improve it by suitable method before construction of
highway embankment to avoid failed it by bearing capacity and excessive settlement, in this thesis
improve soft clay soil by stone columns.
• The percentages of saving cost and minimize the diameter of stone column between ordinary and
optimum method is (32.5%) it is mean preferably used the optimum process.
without improving with improving
d=0.5 h=2 60 61.884
d=0.55 h=3 60 70.826
54
56
58
60
62
64
66
68
70
72
bearingcapacity(kn/m^2)

• At height of highway embankment (H=2m) without improving soft clay soil the foundation failed by
excessive settlement and at height of highway embankment (H=3m) the foundation of soft clay failed
by bearing capacity addition to excessive settlement.
• For height of highway embankment (H=2m) without improving soft clay soil the excessive settlement
reach about (80%) above acceptable limit and For height of highway embankment (H=3m) without
improving soft clay soil the average bearing capacity of soft clay less than about (15%) from allowable
stress applied on foundation by highway embankment and traffic load.
• For height of highway embankment (H=2m) and after improving soft clay soil gat redaction in
settlement about (99%) for certain area replacement ratio (35%).The minimum diameter of stone
columns it need to improve bearing capacity for height of highway embankment (H=3m) is (D=0.55m)
and this diameter of stone columns it is gave about (18%) increase in bearing capacity of foundation.
REFERENCES
[1] Dr. Hussein H. Karim, Dr. Mohammad M. Mahmood & Raida G. Renka, “Soft Clay Soil
Improvement Using Stone Columns and Dynamic Compaction Techniques”, Eng. & Tech. Journal
,Vol.27, No.14,2009
[2] Shaker K.,E. 2013-2014, “Strength Properties of Soft Clays Stabilized With Saw Dust Ashes”,
Submitted to the Building & Construction Engineering Department University of Technology
[3] Klaus Kirsch and Alan Bell 2013, “Ground Improvement“ Third Edition CRC Press Taylor &
Francis Group
[4] Manual Geotechnical Design Standard–Minimum Requirements, State of Queensland (Department
of Transport and Main Roads, February 2015)
[5] Indian Standard design and construction for ground improvement guidelines (part 1 stone columns),
Soil and Foundation Engineering Sectional Committee, January 2003
[6] ShyamalK., B. B. Sc. (CE) M. Eng. (WRE) August 2009, “Highway Embankment Design in
Bangladesh”, School of Civil Engineering College of Engineering and Physical Science, the
University of Birmingham
[7] G. Billoet & J. R. Gauthey, “Recommendations for the design, calculation, construction and quality
control of stone columns under buildings and sensitive structures”, USG, the French geotechnical
union association Version No. 2 - March 16, 2011
[8] Awad A. 2016,“Geotechnical Maps for the Soil of Babylon Governorate Using Geographic
Information” the College of Engineering the University of Babylon
[9] Asst. Prof. Dr. Qassun S. Mohammed Shafiqu and Fadhl Abbas Ahmed Al-Assady. Analysis of
Embankment Supported by Stone Columns Encased with Geosynthetic Material. International
Journal of Civil Engineering and Technology, 6 (10), 2015, pp. 97-107.
[10] Hussein H. Karim, Zeena W. Samueel and Huda K. Karim, Iraqi Gypseous Soil Stabilized by
Ordinary and Encased Stone Columns. International Journal of Civil Engineering and Technology
(IJCIET), 7(6), 2016, pp.179–192.

OPTIMUM DESIGN FOR HIGHWAY EMBANKMENT WITH STONE COLUMN

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OPTIMUM DESIGN FOR HIGHWAY EMBANKMENT WITH STONE COLUMN