19- 25


 

 

    
Al-Khwarizmi 
Engineering   

Journal 
Al-Khwarizmi Engineering Journal,Vol. 12, No. 3, P.P. 19- 25 (2016) 

 

 
Helical Piles Embedded in Expansive Soil Overlaying Sandy Soil 

 
Bushra Suhale  Al-Busoda*             Hassan Obaid Abbase** 
*,**Department of Civil Engineering/ College of Engineering/ University of Baghdad 

E-mail:albusoda@yahoo.com 
E-mail:temimi71@yahoo.com 

 

(Received 8 November  2015; accepted  19 April 2016) 

  
Abstract 
         

In this study, the behavior of square helical piles models (5×5) mm2 embedded in expansive soil bed overlaying a 
layer of sandy soil was investigated. The sand layer 200mm thickness was compacted into four sub layers in a steel 
container with diameter 400mm in size. Sandy soil layer was compacted into two relative densities 40% and 80%. The 
bed of expansive soil 300mm thickness was compacted into six sub layers on sandy soil layer. Model tests are 
performed with helical pile length 350mm, 400mm and 450mm and with helix diameter 15mm and 20mm. Also, one 
helix and double helix were used for these piles. Water was allowed to seep from bottom of sandy soil to reach surface 
of expansive soil through four sand drains around helical pile. This study revealed that the upward movement of helical 
piles decreases with increasing depth of embedment in the sandy layer, helix diameter and number of helix. The 
increase in these parameters provides anchorage against uplifting. Helical piles embedded in sandy soil of relative 
density (40%) have uplift movement more than helical piles of relative density (80%).  

 
Keywords: Helical piles, Expansive soil, Uplift movement.  
 

 
1. Introduction     
        

Foundations on expansive clay are frequently 
subjected to severe movements arising from 
moisture changes within the clay with consequent 
cracking and damage due to distortion. Piles have 
been used extensively for foundations in swelling 
soils in order to anchor the structure down at a 
depth where change in moisture content are 
negligible, so that movements of the structure are 
minimized [8]. The modern square shaft helical 
piles has been refined in shape and size and 
adapted to high strength low alloy steels to 
produce the deep foundation system in use 
nowadays [7]. Helical piles are a factory-
manufactured steel foundation system consisting 
of a central shaft with one or more helix–shaped 
bearing plate [11]. Any deep foundation, such as 
helical pile must embed and transfer load through 
the active zone to stable soil below. The active 
zone is defined as that zone or depth of seasonal 
moisture change, sometimes also called the depth 

of wetting. It is the depth or zone where soil 
expansion or shrinkage forces adversely affect 
deep [9]. Foundation is not sufficiently installed 
below the active zone, as moisture content 
changes, heave or shrinkage forces will be applied 
to the deep foundation which may cause it and the 
structure above to move. The present work aims is 
to investigate the behavior of model helical piles 
embedded in expansive soil overlaying a layer of 
sandy soil. The parameters investigated are the 
length of helical pile, relative density of sandy 
soil, number of helix and helix diameter. 
 
 
2. Material Properties 
2.1. Expansive Soil  
 

The expansive soil used in this study was 
artificially prepared by mixing Iraqi  bentonite 
from Al-Anbar Governorate / Bushayrah Valley, 
35 kilometers southern Al-Waleed Military Base 
from a depth of three and a half meters from 



Bushra Suhale Al-Busoda                Al-Khwarizmi Engineering Journal, Vol. 12, No. 3, P.P. 19- 25 (2016) 

20 
  

natural ground level, with  sandy soil. In order to 
increase the permeability of prepared soil and to 
facilitate and accelerate saturation process, several 
trial mixes of bentonite-sand were performed. A 
ratio of expansive soil to sand of (4/1) was 
selected. At this ratio, the soil remains highly 
expansive and its permeability is increased. The 
results of laboratory tests are shown in Table (1). 
According to the ASTM standard soil 
classification, the soil is classified as (CH). 

 
2.2. Sandy Soil 
 

This soil is used beneath the expansive soil, 
which is used as a stable zone, is poorly graded 
fine clean sand obtained from site in Al-Khalis 
city.  Prior to testing, the sandy soil is dried in 
laboratory by drying oven at 105 oC for 24 hr. then 
sieved on the sieve No.40 to remove the coarse 
particles. Laboratory tests were conducted on the 
sandy soil to determine the physical, mechanical, 
and chemical properties. The results of laboratory 
tests are shown in Table (2).  It should necessary 
to mention here; that the direct shear test was 
performed at relative density of 80% which 
correspond to dry unit weight equal to (15.9) 
kN/m3. According to the ASTM standard soil 
classification, the soil is classified as poorly 
graded sand (SP).   
   
2.3 Model Piles 
      

Thirty two of steel helical piles with length 
ranging from 300mm to 450mm and square solid 
section with dimension (5x5)mm2 were 
manufactured from high resisting steel as shown 
in Plate (1). The experiment program is carried 
out on single pile with different length, helix 
diameter and number of helix. Two diameters of 
helix plate are used 15mm and 20 mm with 
thickness 3mm.  

 

 
 
Plate. 1. Different Types of Helical Piles used in this 
Study.                                                       

   2.4. Soil Container 
 

Soil steel container was made using a 4mm 
thickness plate with internal diameter of 40cm and 
height of 60cm. The base of container is 
supported by four steel rigid legs and contains a 
hole of 2.5cm diameter in the center of the bed to 
connect the valve. This valve is connected to tank 
to perform the saturation process of soil from 
bottom to top of soil. The water level in the tank 
must be usually kept 10cm more than the surface 
of soil. The containers were painted with two 
coats of anti-rust paint and two layers leady base 
to resist corrosion during test period. Plate (2) 
shows the containers and frames used in testing 
models. 

                                                                                                                          

              
 

Plate. 2. Frames and Containers Tests. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

                                                                                                                                                                  
 



Bushra Suhale Al-Busoda                Al-Khwarizmi Engineering Journal, Vol. 12, No. 3, P.P. 19- 25 (2016) 

21 
  

    Table 1, 
    Physical Properties of Expansive Soil. 
         

Value Soil Property Standard Test Name 
2.78 Specific Gravity (Gs) (ASTM D-854) Specific Gravity 

102 Liquid limit (L.L)% 
 
(ASTM D-4318) 

 
Atterbeg Limits 
 

43 Plastic Limit (P.L)% 
59 Plasticity  Index (P.I)% 
53 Clay % 

(ASTM D-422) Grain size analysis 

27 Silt% 
20 Sand% 
٠ Gravel% 

CH Unified Soil Classification System (USCS) 

13.1-13.4 Maximum Unit Weight (kN/m3) 
(ASTM D-1557) 

Standard Compaction and (3/4) 
Energy of  Standard 18-19 Optimum Moisture Content (O.M.C)% 

260 Swelling Pressure (kPa) 
(ASTM D-4526) 
 

Swelling Pressure 

 
  Table 2, 
  Summary of Sandy Soil Properties. 
 

Test Name Standard Property Value 

Grain Size Analysis 
(Sieve Analysis) 

(ASTM D-422) 
Coefficient of Uniformity (Cu) 

 
2.5 

Coefficient of Curvature (Cc) 1.23 
Unified Soil Classification System (USCS) SP 

Specific Gravity (ASTM D-854) Specific Gravity (Gs) 2.69 
Direct shear (ASTM D-3084) Cohesion(kN/m2) 0 
  Angle of Internal Friction(φ°) 37 

  
 
 2.5. Testing Procedure 
        

The soil bed was prepared on a dry density of 
1.335gm/cm3 which corresponds to a water 
content of 2% dry of optimum, from the 
compaction curve of 3/4 Standard Proctor  for the 
expansive soil. Four sand drains were formed 
around the pile using thin walled steel tube (10 
mm diameter and 300mm length). The sand drains 
were spaced 50mm from the pile (center to 
center). The required amount of the oven dried 
natural sandy soil passing sieve No.40 was 
prepared at two dry unit weight. The first unit 
weight is equal to 15.9 kN/m3 to which represents 
the dense state. The second dry unit weight is 
equal to 14.5kN/m3 which represents loose state. 
Torque is applied gradually to driven helical pile 
in the center of surface of expansive soil bed to 
required depth. Enough care and control should be 
taken to keep vertical line of helical pile. 

 
 
 
 
 
 

4. Results and Discussion 
         

Models tests are performed on steel piles 
without helix plates and have the same   square 
cross section (5×5) mm2 of helical piles to assess 
the degree of efficiency gained after introducing 
helical piles. Figures (1) and (2) shows the effect 
of the length of helical piles on its maximum 
uplift movement. In general, the maximum uplift 
movement of piles decreases with increasing its 
length. When full mobilization of the uplift 
movement is achieved, the deeper soil will tend to 
restrain the upper movement and increase the 
anchorage resistance of the pile. It can be seen 
from Figures (1) and (2) that helical piles 
embedded in sandy soil of relative density equals 
(40%) have uplift movement more than helical 
piles embedded in sandy soil of relative density 
equals (80%). The efficiency of helical piles 
embedded to sandy soil decrease with the increase 
of the relative density. The installation of helical 
piles in loose sandy soil leads to be denser and 
increases shear strength. On the contrary, if 
helical pile is installed in dense sandy soil lead the 
soil to be disturbed and decrease shear strength.  



Bushra Suhale Al-Busoda                Al-Khwarizmi Engineering Journal, Vol. 12, No. 3, P.P. 19- 25 (2016) 

22 
  

Also, it can be noticed from Figures (1) and (2) 
that the maximum uplift movement decreases with 
increasing helix diameter. This behavior may be 
attributed to the increase the surface area of part 
of helical pile embedded in sandy soil that causes 
increasing in anchorage resistance.                                                                                                             
      It can be noticed also from Figures (1) and (2), 
the maximum uplift movement decreases with 
increasing number of helix. Figures (3) and (4) 
illustrates the  dimensionless ratio of  the 
maximum uplift movement of pile to the 
maximum uplift movement of soil  surface 
(Spmax/Ssmax) plotted against Ls/H ratio (depth of 
embedment of the pile in sandy soil layer to the 
thickness of expansive soil) for two relative 
densities 40%,80% of sandy soil. The relationship 
is for helical piles with single and double helix 
with two ratios of diameter of helix plate/ 
equivalent diameter of square cross section of 
shaft of helical pile (dh/dpe) 2.68 and 3.57. A 
unique relationship was observed within a limited 
number of model tests performed and for 
specified soil. Extrapolating the results indicate 
the ratio(Spmax/Ssmax)=0 at  different  ratios of 
(Ls/H) according to helix diameter and number of 
helix as shown in Table (3). To reflect the 
required anchorage the required anchorage depth 
to field conditions, the model test would be more 
conservative since the applied load was not 
included in the model tests. However, this depth 
may be proposed for determining a safe anchorage 
depth. 
 
Table 3, 
Analysis of Results for Required (Ls) of Case no 
Upward Movement of Helical Piles. 
 

Required Ls 
(mm) 

Ls/H 
(R.D.) 
% 

dh/dpe 
No.of  
Helix 

306 1.02 
40 

2.68 
Single 

291 0.97 3.57 
204 0.68 

80 
2.68 

Single 
201 0.67 3.57 
234 0.78 

40 
2.68 

Double 
210 0.70 3.57 
174 0.58 

80 
2.68 

Double 
159 0.53 3.57 

 

 
 
Fig. 1. Variation of Maximum Uplift Movement of 
Helical Pile with L/D Ratio for Different Lengths 
and Helix Diameters (Relative Density =40%). 
 

 
 
Fig. 2. Variation of Maximum Uplift Movement of 
Helical Pile with L/D Ratio for Different Lengths 
and Helix Diameters (Relative Density = 80%). 
 

 
 
Fig. 3. Design Chart for Steel and Helical Piles in 
Expansive Soil Embedded in Sandy Soil with R.D. = 
40 %. 

 
 
 

 



Bushra Suhale Al-Busoda                Al-Khwarizmi Engineering Journal, Vol. 12, No. 3, P.P. 19- 25 (2016) 

23 
  

 
 
Fig. 4. Design Chart for Steel and Helical Piles in 
Expansive Soil Embedded in Sandy Soil with R.D. 
=80 %. 

 
       The pullout load test carried out on helical 
piles in expansive soil embedded to sand soil to 
measure the ultimate pullout load capacity with 
swelling effect. After complete saturation and the 
swelling of expansive soil is stopped, pullout load 
is applied on helical piles models and the upward 
movement is measured. The failure occurs when 
observing a certain maximum value of pullout 
load or a large upward movement happened due to 
small increment of applied load, this load is called 
failure pullout load. The results of pullout load 
tests of 32 models are tabulated in Table (4). 
Figures (5) to (8) show the variation of pullout 
load with upward movement for three different 
ratios of (L/D) 62, 71, 80 and two relative 
densities of sandy soil 40%, 80%. The pullout 
load upward movement relations are nonlinear 
and show similar trend of behavior. The failure 
pullout load increased with the increasing length, 
helix diameter, number of helix of helical piles 
and relative density of sandy soil. This may be 
attributed to the effect of anchorage action of 
helical piles and shear resistance mobilized along 
the cylindrical helical pile soil interface. Also, 
when sandy soil is dense the friction force 
between helical pile and soil increased which 
caused high resistance. A comparison between 
steel piles and helical piles in term of failure 
pullout load is shown in Table (4) It can be seen 
clearly that the value of failure pullout load of 
helical piles is approximately (4.7-10.6) times 
higher than that of steel piles when R.D. of sandy 
soil 40% and (2.8-8.1) times when R.D. of sandy  
soil 80%.The results obtained were coinciding 
with that obtained by [10] and [12]. 

 

 
 
Fig. 5. Pullout Load -Upward Movement Curves for 
Steel Pile without Helix (R.D= 40%). 
 

 
 
Fig. 6. Pullout Load -Upward Movement Curves for 
Helical Pile with Single Helix (dh=20mm, R.D= 
40%). 

 

 
 
Fig. 7. Pullout Load -Upward Movement Curves for 
Steel Pile without Helix (R.D= 80%). 
 



Bushra Suhale Al-Busoda                Al-Khwarizmi Engineering Journal, Vol. 12, No. 3, P.P. 19- 25 (2016) 

24 
  

 
 
Fig. 8. Pullout Load -Upward Movement Curves for 
Helical Pile with Single Helix (dh=20mm, R.D= 
80%). 

 
 

5. Conclusions                                                                               
 
1. The upward movement of helical piles for piles 
embedded in expansive soil overlaying a sandy 
soil layer decreases with increasing depth of 
embedment in the sandy layer, helix diameter and 
number of helix those provide anchorage against 
uplifting.                        2. 
Helical piles embedded in sandy soil of relative 
density (40%) have uplift movement more than 
helical piles of relative density (80%). The 
increase in efficiency of helical piles embedded to 
sandy soil decrease with the increasing of the 
relative density.                 
3. The helical piles resist the soil volume changes 
more than steel piles.                                   
4. The failure pullout load increased with the 
increasing length, helix diameter, number of helix 
of helical piles and relative density of sandy soil. 
5. The value of failure pullout load of helical piles 
is approximately (4.7-10.6) times higher than that 
of steel piles when R.D. of sandy soil 40% and 
(2.8-8.1) times when R.D. of sandy soil 80%.      
6. For the specified soil used, there is a unique 
relationship between dimensionless ratio of the 
maximum uplift movement of pile to the 
maximum uplift movement of soil surface 
(Spmax/Ssmax) and ratio of depth of embedment 
of the pile in sandy soil layer to the thickness of 
expansive soil (Ls/H) for loose and dense state of 
sandy soil. This relationship may be used for 
determining the safe depth required to provide 
provide a sufficient anchorage. 
 
Notation 
D  diameter of pile 
dh  diameter of helix plate 
dpe equivalent diameter of square pile  

H thickness of expansive soil 
L length of pile 
Ls embedment length of  pile in sandy soil  
R.D. relative density of soil 
 
 
6.  References 
 
[1] ASTM D422-2007, “Standard Test Method 

for Classification of Soils for Engineering 
Purposes (Unified Soil Classification 
System)”. 

[2] ASTM D3084-2007, “Standard Test Method 
for Direct Shear Test of Soil under 
Consolidated Drained Condition”.                 

[3] ASTM D4318-2007, “Standard Test Method 
for Liquid Limit, Plastic Limit and Plasticity 
Index of Soils”. 

[4] ASTM D4546 (A)-2007, “Standard Test 
Method for One-Dimensional Swell or 
Settlement Potential of Cohesive Soils”.  

[5] ASTM D1557-2007, “Standard Test Method 
for Laboratory Compaction Characteristics of 
Soil Using Standard Effort”.  

[6] ASTM D854-2007, “Standard Test Method 
for Specific Gravity of Soil Solids by Water 
Pycnometer”. 

[7] Black, D., R., and Pack, J., S., ''Design and                
Performance of Helical Piles in Collapsible 
and  Expansive Soil in Arid Regions' 
'Proceeding of 36th Symposium, Engineering 
Geology       Geotechnical    Eng.,   Univ.of 
Nevada, (2001). 

[8] Hari, P., K., and Ramana, V., R., ''Pullout    
Capacity of Granular Anchor Piles in 
Expansive Soils''   IOSR Journal of 
Mechanical and Civil Eng., Vol.5, (2013). 

[9] Hargrave, R.L. and Thorsyen, R.E. ''Helical 
Piers in Expansive Soils of Dallas, Texas'' 
7th Int.       Conf.on Expansive Soil, (1993).   

[10] Hamdy, H., A., and Walla, E., D., ''The 
Compression and Uplift Bearing Capacities 
of Helical Piles  in Cohesionless Soil' 
'Journal of American Science, Vol.9, No.12, 
(2013).       

[11] John, S., Pack and P.E., M., ''Performance of 
Square Shaft Helical Pier Foundations in 
Swelling   Soils'', Geo-Volution, PP.76-85, 
No.4, (2006).   

[12] Tsuha, C.H.C., and Rault, G., ''Influence of 
Multihelix Configuration on the Uplift 
Capacity of  Helical Anchors'', 18th Int. 
Conf.on Soil Mechanics, Paris, (2013). 

 



�� 3، ا���د����12 ا���ارز
� ا����	�� ا����
���ى 	��� ز��ر                                                              �� ،25 -19 )2016( 

 

 
 
 

    ���
  ا��.�-, ا���� �� ا��+�و	� (" &��� ا)$��'�� &%$�� #�"  ط �� ر
  

  **1%0 # �� # �س            * ���ى 	��� ز��ر
��� ا������ /��� ا������ ا������** ، *�  %$�اد"!م�� / 

albusoda@yahoo.com :&ا�-),� ا+�*()و� * 
temimi71@yahoo.com : ا+�*()و�& ا�-),� ** 

  
 

  
��  ا��2

  
�= ط-�0 مA ا�)م@م)%. م��  )٥x٥(<= ھ;ه ا��را�� �8 درا�� 78)ف ا�)�!45 ا���3-�� ذات م0/. م)%. %!%�!د        C ��)�8 ��D!E)ا�()%� . م$)و�� %()%� ا�

 F��% ���م�� ���I �8! ٣٠٠ ا�()%� ا+�(F��% ��D!E %. ٨٠و%٤٠م�� وM*% !���I �8!<� ��-��  ٤٠٠م�� K��I %!ر%. ط-0!ت <= ا�!ء �I,�ى %0/)  ٢٠٠ا�)م
���م�� وا�(�RمK  ٢٠ م�� و١٥ م�� وS5!ET ��3-�� دا5),� %0/)  ٤٥٠ م�� و ٤٠٠ م�� و ٣٥٠ا�(�RمK ر�!45 ��3-�� %!ط3ال . %�K ط-0!ت <3ق ا�()%� ا�)م

�= AC ط),] ار%. م-!زل رم��� 3Iل ا�)��4ةا��!ء اX�Y . %37رة اI!د,� و�W!��5 �*@ ر��4ةC\� .E8(,و ���. ا�= ا�()%� مA ا+�AC @E ط),] ا�()%� ا�)م
 �]�E7ا� (/��= 08@ %!زد,!د ا���] <= ا�()%� ا�)م��� وز,!دة C\� ��-�3��� ا�)�!45 ا�(I ل ھ;ه ا��را�� ان\D Aدھ! و"� م�C�3-�� ا��$)و�� . و�ا�)�!45 ا�

�= ا�M) مA ا��$)و�� <= ذات ا�*M!<� ا���-��  % ٤٠��� ذات ا�*M!<� ا���-�� <= ا�()%� ا�)مC\� !�)�(I 8٨٠*3ن. %