International Journal of Geosciences, 2012, 3, 105-110
http://dx.doi.org/10.4236/ijg.2012.31012 Published Online February 2012 (http://www.SciRP.org/journal/ijg)
Geotechnical Properties of Problematic Soils Emphasis on
Mohsen Rezaei1, Rasoul Ajalloeian2, Mohammad Ghafoori1
1Geology Department of Fredowsi University of Mashhad, Mashhad, Iran
2Geology Department of Isfahan University, Isfahan, Iran
Received September 9, 2011; revised October 7, 2011; accepted November 15, 2011
Soils are unconsolidated materials that are result of weathering and erosion process of rocks. When water content of
some soils change, it makes problems to civil activities. These problems include swelling, dispersing and collapse. The
change of water content of expansive soils causes to changes their volume. The volume change can damage structures
that have built on the soils. In dispersive soils, particles move through soils with water flow. It may be conduits form in
the soils. Collapsible soils are settled when saturated under loading. The rapid collapse of soils damages the structures
which have built on soil. Problematic soils are formed in especial geological conditions. For example, collapsible soils
are often founded in semi-arid area. Field observation and laboratory test can be useful to identify problematic soils.
Some properties of soils such as dry density and liquid limit are helpful to estimate collapsibility potential of soils. In
this regard, it was done a series laboratory tests to evaluate the collapsibility rate.
Keywords: Soil; Collapse; South Rudasht; Dorcheh; Sivand
The earth’s crust is composed of soil and rock. Rock is
often considered a consolidated material but soil is de-
fined an unconsolidated sediment and deposits of solid
particle that have resulted from the disintegration of rock.
Soils can be grouped into two categories depending on
the method of deposition. Residual soils have formed from
the weathering of rocks and remain at the location of their
origin. Residual soils can include particles having a wide
range of sizes, shapes and compositions depending on
amount and type of weathering and the minerals of par-
ent rock. Transported soils are those materials that have
been moved from their place of origin. Transportation may
have resulted from the effect of gravity, wind, water gla-
ciers or human activities. Transported soil particles are
often segregated according to size during the transporta-
tion process. The method of transportation and deposition
has significant effect on the properties of the resulting soil
Many large land areas have been formed with trans-
ported soils which deposited primarily by one of the
transportation methods. The type and condition of soil
deposits underlying proposed construction site must be
recognized. Therefore engineers that engaged with con-
struction has to be considered soil origin and properties
of site especially problematic soils.
2. Problematic Soils
Many soils can prove problematic in geotechnical engi-
neering, because they expand, collapse, disperse, undergo
excessive settlement, have a distinct lake of strength or
are soluble. Such characteristics may be attributable to
their composition, the nature of their pore fluids, their
mineralogy or their fabric .
There are many types of problematic soils, some of the
most noteworthy being swelling clay, dispersive soils and
collapsible soils that discuss subsequently. Present study
is mainly in reflection with collapsible soils. In following,
briefly pay attention to expansive and depressive soils and
finally collapsible soils have been explained.
2.1. Expansive Soils
Some soils undergo slow volume changes when change
water content that occur independently of loading and are
attributable to swelling or shrinkage . These volume
changes can give rise to ground movement which can cause
damage to low-rise buildings that they don’t have suffi-
cient weight to resist [4,5]. These soils also represent a
problem when they are encountered in road construction,
and shrinkage settlement of embankments composed of
such clays can lead to cracking and breakup of the roads
they support. Construction damage is notable, especially
opyright © 2012 SciRes. IJG
M. REZAEI ET AL.
where expansive clay forms the surface cover in regions
which experience alternating wet and dry seasons leading
to swelling and shrinkage of these soils .
The principle cause of expansive soils is the presence
of swelling clay minerals such as Montmorillonite. The
potential for volume change in soil is governed by its
initial moisture content; void ratio and vertical stress as
well as the amount and type of clay minerals . Ce-
mented or undisturbed expansive soils have a high resis-
tance to deformation. Therefore, remolded expansive soils
tent to swell more than undisturbed ones.
2.2. Dispersive Soils
Dispersion occurs in soils when the repulsive forces be-
tween clay particles exceed the attractive forces, thus bring-
ing about deflocculation, so that in the presence of rela-
tively pure water the particles repel each other to form
colloidal suspensions . In non-dispersive soil there is a
definite threshold velocity below which flowing water
causes no erosion. The individual particles cling to each
other and are only removed by water flowing with a cer-
tain erosive energy. By contrast, there is no threshold veloc-
ity for dispersive soil; the colloidal clay particles go into
suspension even in quiet water and therefore are highly
susceptible to erosion and piping. Dispersive soils con-
tain a moderate to high content of clay material but there
are no significant differences in the clay fractions of dis-
persive and non-dispersive soils, except that soils with less
than 10% clay particles may not have enough colloids to
support dispersive piping. Dispersive soils contain a higher
content of dissolved sodium (up to 12%) in their pore wa-
ter than ordinary soils. The clay particles in soils with high
salt contents exist as aggregates and coatings around silt
and sand particles and the soil is flocculated .
The mechanism by which dispersive soil is eroded in-
volves the structure of the soil and the character of the
interaction between the pore and eroding fluids. It would
appear that the stress required to initiate erosion is af-
fected by the type of clay minerals present, pH value,
organic matter, temperature, water content, thixotropy,
and type and concentration of ions in the pore and eroding
fluids. The structure of the soil and the osmotic influences
set up at the surface of clay particles produce swelling at
the particle surfaces. This swelling reduces the interparticle
bonding forces and is a significant factor in the erosion of
cohesive soils by water. The more dispersed the soil sys-
tem is, the greater is the swelling caused by the concen-
tration gradients at the clay particle water interface. For a
given eroding fluid the boundary between the flocculated
and deflocculated states depends on the value of the so-
dium adsorption ratio, the salt concentration, the pH
value and the mineralogy .
2.3. Collapsible Soils
Collapsible soils are moisture sensitive in that increase in
moisture content is the primary triggering mechanism for
the volume reduction of these soils . Soils such as
loess and certain wind-blown silts may have the potential
to collapse. However, these wind-blown deposits are not
the only soils which are capable of collapsing . Col-
lapsible soils normally possess porous textures with high
void ratios and have relatively low densities. They often
have sufficient void space in their natural state to hold
their liquid limit moisture content at saturation. At their
natural low moisture content these soils possess high ap-
parent strength but they are susceptible to large reduc-
tions in void ratio upon wetting . In other words, the
metastable texture collapses as the bonds between the
grains break down when the soil is wetted. Hence, the col-
lapse process represents a rearrangement of soil particles
into a denser state of packing. Collapse on saturation
normally takes only a short period of time .
Identification of collapsible soil is best accomplished
by testing specimens . However, geologic and geo-
morphologic information can be useful in anticipating
collapsible soil deposits. Dry density and liquid limit of
soils can be used to evaluate the collapsibility of soils.
Figure 2, shows the relation between dry density, liquid
limit and collapsibility of soils .
Geotechnical and geological engineers know from ex-
perience that alluvial and wind-blown deposits in arid
regions are likely to exhibit some collapse potential [16,
17]. Since, soils in case studies are mainly collapsible,
it’s necessary to explain the test procedure that employed
in this research.
The collapsible test procedure is that tested an undis-
turbed sample at natural moisture content in oedometer.
A load of 5 kPa is placed on the sample and set the dial
gauge zero. Vertical stress is incrementally increased
until the rate of strain becomes less than 0.1 percent per
hour. Then, increasing the stress is continued until the
stress become more than or at least equal to expected
structure pressure. At this point the sample is inundated
and the resulting collapse strain recorded . Collapsible
index is calculated by Equation (1) :
Ic: collapsibility index
H1: Initial soil sample thickness (before saturation)
H2: Final thickness of the soil sample (after saturation).
The collapsed sample then is subjected to further load-
ing to develop the inundated compression curve. The
amount of collapse of a soil layer is simply obtained by
multiplying the thickness of the layer by the amount of
collapse strain. Table 1 provides an indication of the po-
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M. REZAEI ET AL. 107
tential severity of collapse .
3. Case Studies
Conditions in arid and semi-arid climates favor the for-
mation of the most problematic collapsible soils. Col-
lapsible soils are to be found in many parts of the Iran,
particularly well-known examples being the extensive
deposits of collapsible soils in Esfahan, Fars and Khorasan
provinces. In this section it will be considered three loca-
tions as case studies.
3.1. South Rudasht Irrigation Network Channel
South Rudasht irrigation channel network is located on
south east of Isfahan province. Foundation of main
channel from distance 5 to 13 kilometer composed of
fine grain materials, 2.5 to 3 meters in depth. To identi-
fying geotechnical properties of the soils, picked 6 un-
disturbed samples from 6 points or channel route and
done laboratory test. General properties selected samples
are shown in Table 2.
After determine the physical and plasticity properties
of soil samples, liquid limit of samples are plotted versus
dry density as Figure 2. This figure shows that samples 2
and 3 set under collapse limit line. These samples are
collapsible probably. Other samples set above collapse
line. But they are near the line and it may be collapsible
in low degree.
The soil samples classified in unified system. Results
of classification tests are shown in Figure 1 and Table 3.
Regarding to field observations and Figure 2, samples
2 and 3 have collapse potential. Laboratory tests have
been done in all samples. These results are also certified
the field observation. Results of the collapsibility tests
are shown in Figure 3 and Table 4. Generally, pay at-
tention to Table 4, samples 2 to 5 are high or severe col-
lapsible and need improvement. Samples 1 and 6 have no
critical collapse problem and no need to any improve-
As a result, in comparison between samples 2 and 6,
both soils are almost similar. The only difference is in unit
weight. Due to this difference, sample 2 has more po-
tential for collapse. As it is shown in Figure 2, strain in
sample 2, under vertical stress equal to 100 kPa, has been
changed from 4% to about 17% in saturation conditions.
Regarding to Table 1, it is concluded that sample 2, from
point view of collapsibility, has sever trouble. In contrary,
regarding to sample 6, strain value has been changed from
2% to about 4%, under the same conditions. This sample
has moderate trouble.
3.2. Dorcheh City Health Center
Dorcheh city is located in west of Isfahan city. In order
Table 1. Collapse percentage as an indication of potential
Collapse (%) Severity of problem
0 - 1 No problem
1 - 5 Moderate trouble
5 - 10 Trouble
10 - 20 Severe trouble
Over 20 Very severe trouble
Table 2. General properties of picked samples.
class w (%) γd (gr/
1 5 + 7001 CL 21.12 1.61
2 7 + 0000.8 CL 14.19 1.21
3 8 + 4001 CL 9.15 1.61
4 9 + 8001 CL 9.39 1.63
5 11 + 2000.8 SC 7.17 1.73
6 12 + 6000.7 CL 14.37 1.67
Table 3. Plasticity index of samples.
Sample no. LL (%) PL (%) PI (%)
1 26.16 13.73 12.43
2 27.89 16.89 11.00
3 22.39 11.79 10.60
4 23.58 12.23 11.35
5 24.35 12.89 11.46
Table 4. Severity of collapse in tested soils in south Rodasht.
Sample no. Ic (%) Severity of problem
1 0.498 No problem
2 12.816 Severe trouble
3 14.960 Severe trouble
4 5.659 Trouble
5 6.740 Trouble
6 1.931 Moderate trouble
Figure 1. Grain size distribution results.
Copyright © 2012 SciRes. IJG
M. REZAEI ET AL.
Figure 2. Collapse potential attention to LL and dry den-
Figure 3. Collapse tests results in south Rodas ht.
to subsurface of health center foundation, 3 test pits in
predetermined area is excavated and 8 specimens picked
up to laboratory tests. Laboratory test index has been done
in specimens which results are listed in Table 5. Also,
collapsibility tests were done on 2 samples. As it can be
seen in Figure 4, under 200 kPa loading, strain percent
raised from 2 to more than 4. Regarding to Table 1, it is
concluded that soil has moderate collapse potential.
3.3. Sivand Dam Site
Sivand dam site is located in Fars province at north of
Shiraz. Foundation of dam consists of high thickness of
fine grain alluvium underlying by coarse grain deposits.
Table 6 summarizes some properties on the fine grain
soils. Because of low dry density of some soil samples, it
was possible that collapsible soils be present at the foun-
dation of dam. Therefore, collapsibility tests were done
on selected specimens. Pay attention to dam height and
stresses that will be applied on foundation, saturation
process during tests were done under 600 kPa loading.
Test result shows various amount of collapse potential in
soils. Result of one sample test is shown in Figure 5 that
strain percent changes from 6 to 10 due to saturation.
According to Table 1, this sample category as a moder-
ate trouble from collapsibility view point.
Table 5. General properties of soil samples in Dorcheh city.
1.5 - 2.0CL 36.0 17.0
3.5 - 4.0CL 33.7 16.2 0.14 1.53
5.5 - 6.0CL 25.0 8.5
1.5 - 2.0CL 35.0 17.5
TP-2 3.5 - 4.0CL 36.0 17.5 0.41 1.54
1.5 - 2.0CL 35.0 16.5
3.5 - 4.0CL 34.0 16.5 TP-3
5.5 - 6.0CL 24.5 7.8 0.36 1.57
Table 6. Summery of ge ne ral properties of fine grain soils in
0.074 mm (%)
(gr/cm3) LL (%)PI (%)
18 - 20 65 - 75 1.3 - 1.6 25 - 45 15 - 22
Figure 4. A sample of collapse test result in Dorcheh cit.
Figure 5. A sample of collapsibility test in Sivand damsite.
Base on collapsibility studies in other parts of Iran and
laboratory tests especially in central of Kerman and
Mashhad-Sarakhs road, it is concluded that east and north-
east of Iran has also potential of collapsibility.
4. Improvement Methods of Collapsible Soils
There are various methods to improvement of collapsible
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M. REZAEI ET AL. 109
soils as following:
Since collapse take place when soils are wetted,
flooding of soils before construction can be helpful to
stabilized collapsible soils. Flooding method is useful.
But, in low collapse potential soils, if flooding and load-
ing be together, its result will be better.
Various methods of compaction have been used to den-
sify collapsible soils such as dynamic compaction, vibro-
flotation, vibroreplacement, compaction piles, concrete
compaction piles, compacted soil-cement piles.
However, if the soils contains a high relatively car-
bonate content, it may be difficult to achieve the desired
result with dynamic compaction.
Some types of grouting such as cement, clay, bitumen,
phosphoric acid, silicate and lime grout being injected
under pressure within collapsible soils to stabilize.
Aforementioned methods can be used in various con-
ditions that explain subsequently:
Moistening and compaction with extra heavy impact
or vibratory rollers for thickness of soils about 1 meter
can be useful . In south Rudasht project used flooding
method as channel made without concrete lining and ap-
plied channel for one irrigation period, existence of water
and weight of channel embankment caused occur col-
lapses in soils. Then, it has been made concrete lining of
Over-excavation and re-compaction with or without addi-
tives such as cement or lime, vibroflotation, vibro-replace-
ment, dynamic compaction, compaction piles injection of
lime, lime piles and columns, Jet grouting and Ponding
or flooding when no impervious layer exists and heat treat-
ment to solidify the soils in place are useful for soil about
1.5 to 10 meters thick. Dynamic compaction is used in
Sivand dam foundation for collapsible soils treatment. But,
it isn’t being useful because of high thickness of soils
and used replacement of soils with suitable soils [7,9,13].
When collapsible soil thickness is more than 10 meters,
any of the aforementioned or combinations of the afore-
mentioned methods, where applicable can be used.
Possible future methods may be used listed follow:
Ultrasonic waves to produce vibrations that will des-
troy the bonding mechanics of the soil.
There are many types of problematic soils. Some of
the most noteworthy are swelling clay, dispersive soils
and collapsible soils.
Collapsible soils are often found in arid and semi-arid
areas. In most part of Iran especially in central parts,
collapsible soils were founded.
Although wind-blown soils have more collapse be-
havior, but collapsibility behavior are seen in other
type of soils such as clay and silt.
Significant settlements can take place in foundation
of structures on collapsible soils after they have been
saturated. These have led to structure damage.
Determining of physical properties such as dry den-
sity and liquid limit of soils can be helpful to identify
collapse potential of soils.
Collapse potential reduces by increasing dry density
and liquid limit of soil. To identify detail of collapse
potential, laboratory tests have needed.
Collapsible soils have high porosity. During collapse
test, bonds between soil particles destroy and soil par-
ticles re-arranged in denser array, and it caused to
collapse the soil.
There are several methods to improvement of col-
lapsible soils. It can be used one method or combina-
tion of different methods, depend on project conditions.
In most conditions, saturation of soils before construc-
tion can be helpful to stabilized collapsible soils. It
will be best result when saturating and loading is done
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