Agus Setyo Muntohar

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106 
Civil Engineering Dimension, Vol. 8, No. 2, 106–110, September 2006 
ISSN 1410-9530 
 
Civil Engineering Dimension 
ISSN 1410-9530 print © 2007 Thomson GaleTM 
http://puslit.petra.ac.id/journals/civil 
Technical Note 
 
THE SWELLING OF EXPANSIVE SUBGRADE AT WATES-
PURWOREJO ROADWAY, STA. 8+127 
 
 
Agus Setyo Muntohar 
Doctorate Fellow, Department of Construction Engineering, National Taiwan University of Science and 
Technology, Taipei, Taiwan, Republic of China 
Senior Lecturer, Department of Civil Engineering, Muhammadiyah University of Yogyakarta. Indonesia. 
Email: muntohar@umy.ac.id 
 
 
Catatan Redaksi: 
Kerusakan struktur bangunan dan perkerasan jalan karena tanah ekspansif merupakan masalah yang 
banyak terjadi di Indonesia. Salah satu kerusakan perkerasan jalan yang terjadi karena tanah ekspansif 
adalah kerusakan perkerasan jalan di Sta. 8+127, Jalan Raya Purworejo-Wates. Technical Note ini 
menyajikan penyelidikan penyebab kerusakan perkerasan jalan tersebut. Penulis menyimpulkan bahwa 
tanah dasar di lokasi tersebut adalah tanah ekspansif dengan tekanan mengembang yang sanggup merusak 
struktur perkerasan jalan di atasnya. 
 
 
Note from the Editor: 
Damage of structures and road beds due to expansive soil are common in Indonesia. One example is the 
deterioration of a road section at Sta. 8 + 127 of the Purworejo-Wates Highway. This Technical Note presents 
the investigation of the cause of the deterioration of the road bed. The author concludes that the sub grade is an 
expansive soil and the swelling pressure is able to lift the overlaying pavement and cause considerable cracking. 
 
 
BACKGROUND 
 
Expansive soils are widely distributed in the world 
and found in more than 60 countries and regions. 
The problem of expansive clay is a worldwide issue. 
Kaczyński and Olszewska [1] showed that swelling 
soil in Poland had brought relatively many failures 
of structures. An investigation undertaken by Shi et 
al [2] reported that China was one of the countries 
with a large distribution of expansive soils, 
occupying nearly 600,000 km2. Expansive soil 
constitutes the most vulnerable natural hazard to 
buildings on shallow foundations in China. Yanjun-
Du et al [3] indicated that the most detrimental 
effect of embankment and roadbeds in Ning-Liang 
highway were due to ignorance of this problem. A 
serious damage and financial lost was also 
experienced in Oman. These problems were mainly 
caused by expansive soil and rock, which undergo 
volumetric change upon wetting and drying [4]. 
Erguler and Ulusay [5] reported that the expansive 
soils in Turkey were found in abundance in central, 
western and southern parts of Ankara city which 
was the capital of Turkey, due to the fact that some 
lightly trafficked roads were rough and damages to 
low-rise buildings.  
 
Cohesive soils present in a region of Yogyakarta are 
highly sensitive to the action of weathering. At 
natural conditions, weathering causes soil disinte-
gration and leads to deterioration of the physical and  
  
 
Note: Discussion is expected before November, 1st 2006. The 
proper discussion will be published in “Dimensi Teknik Sipil” 
volume 9, number 1, March 2007. 
mechanical properties of cohesive soils. Some clay 
soils exhibit a certain level of swelling–shrinkage 
even if their swelling grades are relatively low. The 
swelling–shrinkage is most influenced by the 
mineral composition and clay content. The dynamic 
of swelling is also influenced by various factors such 
as soil lithology, availability of exchangeable cation, 
percentage of carbonates, structure and microstruc-
tures, and the environmental effects (water table 
fluctuation, moisture content, degree of compaction, 
and drainage system). When, the clay soil was in the 
disturbed conditions and compacted, and then used 
for roadway subgrade, foundation, embankment or 
road-bed, their natural structures were destroyed. 
This phenomena will take effect on some changes 
such as broken cementing bonds, increased water 
content, higher dry density and increased swelling–
shrinkage indexes. This results in decrease in 
bearing capacity and increase in deformation of 
foundation. The soil may become high swelling grade 
expansive soil. This swelling–shrinkage cycles play 
fundamental role in this process and bring about 
serious damage.  
 
Muntohar [6] reported that the swelling pressure of 
expansive subgrade might generate some pavement 
distress at Yogyakarta – Wates roadway. Similar 
case was observed at Wates – Purworejo roadway 
(Figure 1). The pavement cracking at this route 
should be paid a great attention since the roadway 
links two provinces, D.I. Yogyakarta and Central 
Java. This route is also called as the Southern Route 
(Jailor Sultan), which is an alternative route beside 
the Northern Route (Jailor Pentair Tara). This paper 
presents the investigation on the swelling charac-
A S Muntohar / Expansive Subgrade at Wates-Purworejo Roadway, STA. 8+127 / CED, Vol. 8, No. 2, 106–110, September 2006 
 107
teristics and change in bearing capacity of subgrade 
at STA. 8+127 Wates–Purworejo roadway. The 
research is addressed to highlight the properties of 
subgrade that caused pavement deterioration. 
 
 
Figure 1. Map of road deterioration conditions and location of 
the study. 
 
 
LABORATORY TESTS SCHEME 
 
The soil samples were obtained from the site at near 
STA. 8+127 Wates – Purworejo roadway. The undis-
turbed samples were taken in a depth between 0.5 – 
1.0 m from ground surface, at three different 
locations along the roadway. Series of laboratory 
tests were undertaken to investigate the index and 
some engineering properties, like grain size distri-
bution, consistency limits, specific gravity, Proctor's 
standard compaction, California bearing ratio (CBR), 
and swelling test. The CBR and swelling tests were 
carried out for both disturbed and undisturbed soils. 
The soils tested for CBR was assessed in two 
conditions i.e. soaked and unsoaked. The CBR test is 
in accordance to ASTM D1883-99. The disturbed 
soils were compacted using Proctor's standard 
compaction mold at the optimum moisture content 
(OMC) to attain the maximum dry density (MDD).  
 
The swelling test was done in accordance to Method-
A of ASTM D4546-90. The undisturbed or disturbed-
compacted samples were molded in a 50 mm dia-
meter and 20 mm height. The soil specimen was 
restrained laterally and loaded axially in a consoli-
dometer with access to water. The specimen was 
inundated and allowed to swell vertically at the 
seating pressure. Pressure of at least 1 kPa (20 psi) 
was applied by the weight of the top porous stone 
and load plate until primary swell is completed. The 
specimen was loaded incrementally after primary 
swell has occurred until its initial void ratio/height is 
obtained. 
RESULT AND DISCUSSION 
 
Index Properties 
 
The laboratory test carried out has been focused to 
investigate the particle size distribution, level of 
compaction (maximum dry density), optimum mois-
ture content, soil bearing ratio, and the potential to 
heave vertically of the subgrade. Table 1 presents 
the results of index properties of investigated soil. 
 
Table 1. The index properties of tested soil samples 
Specific 
Gravity 
Natural 
Moisture 
Liquid 
Limit 
Plastic 
Limit 
Plasticity 
Index 
Shrinkage 
Limit 
Liquidity 
Index 
Clay Size 
Fraction Location 
Gs wN (%) LL (%) PL (%) PI (%) SL (%) LI < 2 m (%) 
WP-1 2.56 45.50 85 41 44 16 0.10 32 
WP-2 2.56 45.07 88 43 45 13 0.05 46 
WP-3 2.66 45.12 55 32 24 14 0.57 15 
 
According to the data given in Table 1, the soils are 
classified into elastic silt soil or MH in accordance to 
ASTM classification and A-7-5 according to 
AASHTO. The soils are in plastic state range in 
nature as indicated by value of the liquidity index. 
The liquidity index measures the state or potential 
state of consistency of a natural soil [7]. The most 
important consistency index is the plasticity index, 
PI. In general, the larger the plasticity index implies 
the greater engineering problems associated with the 
use of the soil as an engineering material, such as 
road subgrade, foundation support for residential 
building, etc. 
 
Many soils properties and engineering behaviors 
have been correlated with the plasticity index 
including swelling-shrinkage potential. Eventhough, 
most of the correlation should be cautiously treated, 
some are reasonably reliable, but many are slightly 
better than guesses. Seed et al [8] and Chen [9] 
proposed a very simple model using plasticity index 
parameters to assess the swelling potential of clay 
soils as given in equation (1) and (2) respectively: 
SP = 60 K (PI)2.44 (1) 
SP = B eA(PI) (2) 
 
Where, SP is swelling potential, K = 3.6 x 10-5, A = 
0.0838, B = 0.2558 are constants, and PI is plasticity 
index. Using equation (1), the swelling potential for 
each tested location is 22%, 24%, and 5% respectively 
for soils at WP-1, WP-2 and WP-3. Predicting the 
swelling potential using equation (2) results 10%, 
11%, and 2% respectively for tested soils at WP-1, 
WP-2 and WP-3 location. Further, the degree of 
expansiveness of the soil can be classified into 
medium to high according to Seed et al [8] 
classification and low to high according to Muntohar 
[10] as presented in Table 2.  
 
Location of 
study STA. 
A S Muntohar / Expansive Subgrade at Wates-Purworejo Roadway, STA. 8+127 / CED, Vol. 8, No. 2, 106–110, September 2006 
 108
Table 2. Classification of degree of swelling 
Degree of 
expansion 
Swelling Potential (%), 
Seed et al [8] 
Swelling Potential (%), 
Muntohar [10] 
Very high > 25 > 27.8  
High 5 – 25 16.3 – 27.8 
Medium 1.5 – 5 7.1 – 16.3 
Low 0 – 1.5 0 – 7.1 
 
The potential to swell vertically indicates percentage 
of the volume change of the soil in nature. When the 
expansive soils are soaked, the water rise vertically 
to the surface. The potential vertical rise (PVR) 
depends on the surcharge load and percentage of 
volume change. The PVR value and potential to 
swell vertically, so far is considered to have an effect 
on the larger deformation of road surface [11]. 
 
Swelling properties and soil bearing capacity 
The vertical swelling test in the laboratory gives two 
swelling properties, percent of free swell and swell 
pressure. Free swell is determined after the seating 
pressure was unloaded and the specimen was 
inundated to allow the vertical swell. Table 3 pre-
sents the swelling properties of the tested soils. 
 
Table 3. The swelling properties of tested soil sam-
ples 
Free Swell (%) Swell Pressure (kPa) 
Locations 
Natural dry 
density  
(kN/m3) 
Undis-
turbed 
Com-
pacted 
Undis-
turbed 
Compac-
ted 
WP-1 11.5 1.55 6.61 22 196 
WP-2 11.7 0.72 6.05 22 238 
WP-3 12.4 0.55 1.71 11   39 
 
Vertical swelling of the subgrade will decrease the 
bearing capacity since it increases  void ratio and 
water content. The vertical heave of the undisturbed 
soils does not exhibit extreme degree of expansive-
ness. It can be categorized into low expansive, 
however, the swelling increase after compacting at 
their MDD about 300, 700, and 200 percents 
respectively for tested soil at location WP-1, WP-2, 
and WP-3. This characteristic is possibly caused by 
increasing of the density and reduction of water 
content as shown in Figure 2. The soil at location 
WP-3 exhibits lower swelling compared to the other 
although its dry density in nature is higher. It is 
possibly owing to the soil contains lesser clay fraction 
and the soil incline to behave a liquid state in nature. 
El-Sohby and Rabba [12] also mentioned that there 
are three factors that most influence the swelling 
and swelling pressure of clayey soils i.e. initial water 
content, clay fraction, and initial dry density. 
 
During vertical heave, the vertical pressure occurs 
and then crack propagation develops at pavement 
surface. The strength and stiffness of the pavement 
layers have to be able to restrain the uplift pressure 
to prevent the cracks. A low swelling pressure will 
not cause any extreme distress of the pavement. The 
investigation shows that after compacting to their 
MDD, the swelling pressure of the soil samples 
increase 4–11 times from the natural conditions 
(undisturbed). This characteristic, that compaction 
would result in greater vertical swelling and swelling 
pressure, should be noticed. However, on the other 
side, compaction is an easy and cheap method to 
enhance the soil bearing and reducing soil com-
pressibility of cohesive soils. Table 4 shows that the 
CBR values of compacted soils are higher than the 
undisturbed soils. In general, the soils at the 
observed location have a lower bearing capacity i.e. 
1.1% to 2.8%. 
 
0
1
2
3
4
5
6
7
10 11 12 13 14
Dry density (kN/m3)
Fr
ee
 s
w
el
l (
%
)
Undisturbed
Compacted
WP-3
WP-2
WP-1 (a)
0
1
2
3
4
5
6
7
30 35 40 45 50
Water content (%)
Fr
ee
 s
w
el
l (
%
)
WP-3
WP-2
WP-1 (b)
 
Figure 2.  Effect of (a) dry density and (b) water content on 
vertical swell. 
 
For cohesive soils, the soils absorb much water 
during soaking process and then result in increasing 
of void ratio. The void between soil particles is filled 
with water and reduces the particle bonds. Conse-
quently, the soil is in a looser condition and results in 
a lower bearing capacity. This characteristic is 
shown in Figure 3. 
A S Muntohar / Expansive Subgrade at Wates-Purworejo Roadway, STA. 8+127 / CED, Vol. 8, No. 2, 106–110, September 2006 
 109
Table 4. The compaction and bearing capacity of the 
soil samples. 
Compaction CBR (%) 
MDD OMC Undisturbed Compacted Loca-tions (kN/m3) (%) Normal Soaked Normal Soaked 
WP-1 12.1 35.74 2.8 1.6 7.8 3.8 
WP-2 12.3 35.50 2.8 2.0 7.6 2.8 
WP-3 13.0 35.58 1.1 1.1 6.2 3.5 
 
In road construction, the pavement layers are 
designed based on the value of soil bearing capacity 
and the traffic load. In principal to prevent crack 
propagation, the weight of pavement has to be bigger 
than the swelling pressure. If the swelling pressure 
is higher than the pressure generated from 
pavement materials and traffic load, cracks will 
appear on road pavement as an initial deterioration. 
Figure 4 illustrates the load and pressure induced on 
pavement systems i.e. traffic load, σtraffic, weight of 
pavement materials, σpavement, and swelling pressure, 
σswell. The total stress is defined as resultant of the 
stress working on the pavement. For the existing 
road observed, the pressures are calculated as 
follows, σtraffic = 16.4 kPa, σpavement = 17.1 kPa. It is 
shown that the weight of the pavement layers is 
lower than the swelling pressures. Therefore the 
vertical heave pressure will lift the pavement and 
then caused larger deformation owing to traffic load. 
It is concluded that the swelling pressure of the 
subgrade attributes the roadway deterioration at 
STA. 8+127, Wates – Purworejo route. 
 
0
2
4
6
8
10
0.8 0.9 1.0 1.1 1.2 1.3
Void ratio (e)
C
B
R
 (%
)
WP-3
WP-2
WP-1
Soaked
Unsoaked
 
Figure 3. Effect of void ratio on CBR value of tested soils. 
 
 
 
 
 
 
 
 
 
 
 
Figure 4. The schematic diagram of pressures induced on 
pavement. 
CONCLUSIONS 
 
The laboratory tests have been undertaken success-
fully, and the analysis has proven that the deteriora-
tion occurred at the tested location can be attributed 
to the swelling pressure of the expansive subgrade. 
Furthermore, the followings can be concluded: 
1. The subgrade consists of predominantly silt and 
clay and was classified as highly expansive soils. 
2. In natural conditions, the observed subgrade has 
a low bearing capacity and vertical swell, 
however, the swelling pressure has enough power 
to lift up the pavement layers. 
3. The swelling and swelling pressure of the 
compacted subgrade highly exceeded the ones of 
the natural subgrade. The heave caused a 
decrease in the bearing capacity.  
4. Compaction increased the bearing capacity of the 
subgrade, consequently with an increase in the 
swell and swelling pressure.  
 
 
REFERENCES 
 
1. Kaczyński, R, and Olszewska, B.G., Soil 
mechanics of the potentially expansive clays in 
Poland, Journal of Applied Clay Science, Vol. 11, 
1997, pp. 337-355. 
2. Shi, B., Jiang, H, Liu, Z., and Fang, H.Y., 
Engineering geological characteristics of 
expansive soils in China, Journal of Engineering 
Geology, Vol. 67, 2002, pp. 63–71. 
3. Yanjun-Du, Lin S., and Hayashi S., Swelling–
shrinkage properties and soil improvement of 
compacted expansive soil Ning-Liang China, 
Journal of Engineering Geology, Vol. 53, 1999, 
pp. 351 – 358. 
4. Al-Rawas, A.A., Guba, I., and McGown, A., 
Geological and engineering characteristics of 
expansive soils and rocks in northern Oman, 
Journal of Engineering Geology, Vol. 50, 1998, 
pp. 267–281. 
5. Erguler, Z.A., and Ulusay, R., A simple test and 
predictive models for assessing swell potential of 
Ankara (Turkey) Clay, Journal of Engineering 
Geology, Vol. 67, 2003, pp. 331–352.  
6. Muntohar, A.S., Swelling characteristics of 
expansive clay stabilized with LRHA, Seminar 
Nasional Bidang Keteknikan, 22 February 2001, 
Universitas Muhammadiyah Yogyakarta. 
7. Bowles, J.E., Physical and Geotechnical 
Properties of Soils, 2nd Edition, McGraw-Hill 
Inc., 1984, Ch. 2, p. 42-43. 
8. Seed, H.B., Woodward, R.J., and Lundgren, R., 
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clays, Journal of Soil Mechanics and Foun-
σswell 
Traffic 
Asphalt layer 
σpavement 
σtraffic 
Base course 
Sub-base layer 
Subgrade 
120 mm
350 mm
300 mm
A S Muntohar / Expansive Subgrade at Wates-Purworejo Roadway, STA. 8+127 / CED, Vol. 8, No. 2, 106–110, September 2006 
 110
dation Division ASCE, Vol. 88 No. SM3, 1962, 
pp. 53 – 87. 
9. Chen, F.H., Foundation on Expansive Soils, 
Elsevier Scientific Publishing Co., 1983, Ch. 1, p. 
20-21. 
10. Muntohar, A.S., A Simple predictive model for 
swelling potential of expansive clay soils, Jurnal 
Teknik Sipil, Vol. 9, No. 2, 2003, pp. 263-275. 
11. American Association of State Hghway and 
Transportation Officials, AASHTO Interm 
Guide for Design of Pavement Structure, 
Washington D.C., 1986. 
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19-39. 
 
 



THE SWELLING OF EXPANSIVE SUBGRADE AT WATES- PURWOREJO ROADWAY, STA. 8+127

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THE SWELLING OF EXPANSIVE SUBGRADE AT WATES- PURWOREJO ROADWAY, STA. 8+127

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