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This paper aims to identify the factors that cause damages to buildings constructed on expansive soils and suggests practical solutions to avoid swelling problems. Literature of buildings failures associated with expansive soils and techniques experienced to prevent the swelling damages were intensively reviewed. Three regions in Khartoum state, famous expansive soil areas were selected for this study. Ten cases of damaged buildings were randomly selected for investigation. A field survey of damages was conducted to diagnosis and point out the causes, extent and type of damage that was observed in the buildings. It was observed that eight lightweight buildings suffered heavy damages and only two other buildings were slightly damaged. Common failures observed were cracks in walls and floors, foundation movements, column buckling, sagging of beams and slabs in typical damage cases. It was found that poor surface drainage, gardens watering close to buildings, source of water leakage and improper design of foundation contribute to most failures and damages in buildings. Based on the causes of failure and other factors, practical measures are suggested for the damaged buildings. Finally, conclusions are drawn from the study findings.
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International Journal of Multidisciplinary and Scientific Emerging Research
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108| International Journal of Multidisciplinary and Scientific Emerging Research, Vol.6, No.2 (May 2017)
RESEARCH ARTICLE
Damages of Buildings on Expansive Soils: Diagnosis and Avoidance
Magdi M. E. Zumrawi1, Asim O. Abdelmarouf2, and Abubakr E. A. Gameil3
1Associate Professor, Department of Civil Engineering, Faculty of Engineering, University of Khartoum, Khartoum, Sudan
2,3M.Sc. Student, Department of Civil Engineering, Faculty of Engineering, University of Khartoum, Khartoum, Sudan
Accepted 10 March 2017, Available online 16 May 2017, Vol.6, No.2 (May 2017)
Abstract
This paper aims to identify the factors that cause damages to buildings constructed on expansive soils and suggests
practical solutions to avoid swelling problems. Literature of buildings failures associated with expansive soils and
techniques experienced to prevent the swelling damages were intensively reviewed. Three regions in Khartoum state,
famous expansive soil areas were selected for this study. Ten cases of damaged buildings were randomly selected for
investigation. A field survey of damages was conducted to diagnosis and point out the causes, extent and type of damage
that was observed in the buildings. It was observed that eight lightweight buildings suffered heavy damages and only two
other buildings were slightly damaged. Common failures observed were cracks in walls and floors, foundation
movements, column buckling, sagging of beams and slabs in typical damage cases. It was found that poor surface
drainage, gardens watering close to buildings, source of water leakage and improper design of foundation contribute to
most failures and damages in buildings. Based on the causes of failure and other factors, practical measures are
suggested for the damaged buildings. Finally, conclusions are drawn from the study findings.
Keywords: Damages; diagnosis; expansive soil; buildings.
1. Introduction
Expansive soils pose a significant hazard to foundations of
buildings founded in them. Such soils can exert uplift
pressures which cause considerable damage to lightly
loaded structures. The annual cycle of wetting and drying
causes the soil to swell and shrink. Thus, the arid and
semi-arid regions are much susceptible to damage from
expansive soils throughout the year. In Sudan, the climate
is semi arid and over one-third of the country land covered
with expansive soils. Unfortunately, this area includes
most of the nation's population cities and development
projects. Many houses in central and eastern regions of
Sudan were damaged due to soil heave, [1].
The presence of expansive soils in Khartoum has
contributed to light buildings damages and subsequently
causing increased annual repair expenditure, [2]. Many
structures constructed on swelling clays have met with
widespread problems associated with serviceability
performance mainly in form of cracks or permanent
deformation. There are many cases of residential buildings
have experienced significant cracking and damages, [2].
Engineering problems due to expansive soils have been
reported in many countries, costing millions of dollars due
to severe damages of structures. Maintenance and repair
cost can exceed the original cost of the foundation and
creates financial burden to the owner, [1].Generally, the
damage will result in economic loss for building owners
and the country at large scale. Although the accusing
finger is mainly pointed at the expansive soils, other
contributing factors such as poor design, poor
construction, inadequate supervision of the construction
processes, poor drainage, gardens and big trees close to the
building, and climatic factors have contributed to the
problem.
The object of this research work is to identify the
factors that cause failures to buildings constructed on
expansive soil areas in Khartoum state. Some existing
residential buildings suffered from damages by expansive
soils were taken as a case study. Building sites were
visited to inspect and ascertain some practices on site
likely to cause damage or even collapse of buildings in
order to recommend appropriate remedial measures.
2. Literature Review
2.1 Expansive Soil
Expansive soils are clay soils containing considerable
amount of montmorillonite mineral which has a potential
for swelling or shrinking due to changes in its moisture
content. Expansive soil can be classified into two main
groups with respect to the parent rock. The first group
comprises the basic igneous rocks such as the basalts in
India and South Africa. In this group, the Feldspar and
Magdi M. E. Zumrawi et al Damages of Buildings on Expansive Soils: Diagnosis and Avoidance
109| International Journal of Multidisciplinary and Scientific Emerging Research, Vol.6, No.2 (May 2017)
Pyroxene minerals of the parent rocks have decomposed to
form montmorillonite and other secondary materials. The
second group comprises the sedimentary rocks that contain
montmorillonite as a constituent which breaks down
physically to form expansive soils. Examples of this type
of rock are bedrock shale found in North America and the
shale in South Africa, [3]. The three most important
minerals of expansive clay are montmorillonite, illite and
kaolinite. The montmorillonite is considered as a highly
expansion and the most effective one for swelling
behavior, [4].
Potentially swelling clays can be recognized in the
laboratory by their plastic and swelling properties.
Generally, clays of high plasticity usually have high
swelling potential. Expansive soils are characterized by
plasticity index over 30%, liquid limit exceeding 50% and
have high swelling potential, [3]. In the field, expansive
clays can be recognized in the dry season by the deep
cracks of roughly polygonal patterns, [5]. Three
ingredients that are necessary for soil to swell, clay rich of
montmorillonite mineral; when the natural water content is
around the plastic limit of the soil; and there is a source of
water leakage.
Expansive soils experience volume changes as a result
of moisture changes leading to differential movements
below a building‟s foundation. When a structure builds on
such a soil, it applies an upward pressure on the
foundation. If the foundation transfers a downward stress
which is smaller than the swelling pressure, the foundation
moves upward. These upward and downward movements
of foundations become cyclic seasonal movements during
the entire life span of the structure. These cyclic
movements tend to tear up the walls and eventually
destabilize the whole structure. Light structures, such as
single or double storey buildings, pavements, etc. which
generally transmit smaller stresses to the soil than the
swell pressure are greatly suffered the damage, [6].
2.2 Damages in Buildings
Different Buildings experience various levels of damages
during their life time. Damages may occur within a few
months following construction, may develop slowly over a
period of about 5 years, or may not appear for many years
until some activity occurs to disturb the soil moisture, [7].
The probability of damages increases for structures on
swelling foundation soils if the climate and other field
environment, effects of construction, and effects of
occupancy tend to promote moisture changes in the soil.
The differential movement caused by swell or shrinkage of
expansive soils can increase the probability of damage to
the foundation and superstructure. Differential rather than
total movements of the foundation soils are generally
responsible for the major structural damage. Differential
movements redistribute the structural loads causing
concentration of loads on portions of the foundation and
large changes in moments and shear forces in the structure
not previously accounted for in standard design practice,
[6]. The damages are due to design faults, cheap
construction materials, poor workmanship, poor drainage,
climatic condition and swelling behaviour of expansive
soils.
The volume change behavior of expansive soil generates
serious damage to civil infrastructures in Sudan and many
countries over the world. In general, the annual damage in
Sudan exceeds $6million and most of the annual damage
reported occurs in residential and commercial buildings,
[1]. Previous studies indicated a continual increase in
annual damage caused by expansive soil as the population
continues to grow due to the need of new developments to
the expanding residential buildings and commercial
markets,[7][8]. Rosenbalm and Zapata [9] stated that in
the United States alone, the cost to repair structures
damaged by expansive soils has been estimated to be twice
the combined damages of natural disasters. Expansive
soils have reportedly inflicted billions of dollars in
damages and repairs annually to structures, [10].
Evaluation of damages has to base on experience and
knowledge of the history of the building, construction
materials details, crack patterns, and existing physical
condition. This is possible by means of walk through
inspection to identify and categorize both distinct and
hidden damages. For all damages, the professional
inspector must predict a complete set of causes and
effects. The correlation between causes and effects require
experimental and analytical investigation. This is used to
identify, localize and quantify the damages for structural
performance evaluation. Damage evaluation based on
different deterministic criteria in relation with angular
distortion, [11][12].
The most obvious identifications of damage to
buildings are doors and windows that get jammed, uneven
floors, and cracked foundations, floors, masonry walls and
ceilings. Moreover, different crack patterns mean different
causes for different foundation materials. In most cases,
cracks due to shrinkage and expansive clay usually run
from corner towards adjacent opening and are uniform in
width or v-shaped, wider at the top than the foundation
wall, [13][14]. This pattern of cracks happens when the
moisture movement is from the perimeter to the centre of
the house. In some cases, the cracks are wider at the
bottom than the top due to dishing effect as opposed to
dooming effect. This happens when the moisture moves
from centre to the perimeter resulting into the saucer
effect. In the dishing effect, the cracks are wider bottom
than top because of the inwards tilt, [15]. Cracks due to
structural failure are significant cracks and caused due to
improper design and/or quality control failure. Besides
functions and cost such cracks have psychological impact
on the owners and can be encountered in high-rise
building and in non-expansive soil areas. Such cracks
occur very rarely. Crack due to foundation movement are
usually associated with expansive soil, which can exert a
pressure which moves the structure. The pattern of the
cracks depends on whether it is a doming heave or a dish
shaped lift heave. Figure 1 schematically illustrates some
commonly observed exterior cracks in brick walls from
doming or edge down patterns of heave. The pattern of
heave generally causes the external walls in the
superstructure to lean outward, resulting in horizontal,
vertical, and diagonal fractures with larger cracks near the
top, [16].
Magdi M. E. Zumrawi et al Damages of Buildings on Expansive Soils: Diagnosis and Avoidance
110| International Journal of Multidisciplinary and Scientific Emerging Research, Vol.6, No.2 (May 2017)
Figure 1 Cracks patterns on exterior wall resulting from
dome heave of foundation soil, [16]
The classification of the damage is very important to
assess whether the building calls for strengthening, repair,
renovation or demolition. Various researchers ([17],[18],
[11]) put forward many definitions, specifications,
classification and effect of damage in structures as given
in Table 1.
2.3. Practical Solutions for Swelling
In order to minimize or eliminate the danger of damage of
buildings because of heave and shrinkage, the methods
commonly have been used are moisture control, soil
stabilization and structural measures.
2.3.1 Moisture Control Barriers
The main cause of heave and shrinkage is the fluctuation
of moisture under and around the structure. In general, the
natural ground water fluctuates depending on land
topography, geological and weathering conditions. In a
country like Sudan, where there are distinct dry and wet
seasons, the fluctuation of ground water table during these
periods is large.
Generally, expansive soil will not be a problem if the
moisture content is constant throughout the soil. Moisture
fluctuation can be controlled by using horizontal barriers,
vertical moisture barriers, subsurface and surface drainage,
[19].
Table 1 Classification and effect of damages in buildings, [11]-[17]
Degree of
Damage
Description of damage
Effect of damage
on building
Crack width
(mm)
Insignificant
Hairline cracks
None
< 0.1
Very slight
Fine cracks
None
0.1 to 0.3
Slight
Cracks are visible and easily filled. Several slight fractures may appear
inside of the building. Doors and windows may stick
Aesthetic only
0.3 to 2
Moderate
Cracks that require opening up and patching. Possible replacement of a
small amount of brickwork. Doors and windows stick, service pipes may
fracture.
May affect serviceability and
stability of the building
2 to 5
Severe
Large cracks require extensive repair work involving breaking-out and
replacing sections of walls. Windows and door frames distort and floor
slopes are noticeable. Leaning or bulging walls. Beams lose some bearing.
Utility service disrupted
Serviceability and stability of
the building at risk.
5 to 25
Very severe
Major repair involving partial or complete rebuilding. Beams lose bearing,
walls lean badly and require shoring and windows are broken with
distortion.
There is a danger of structural
instability
>25
Horizontal moisture barriers can be installed around a
building in the form membranes, rigid paving or flexible
paving. Widely used horizontal barriers are polyethylene
membrane, concrete aprons and asphalts membrane. The
purpose of the horizontal barriers is to prevent excessive
intake of surface moisture, [10].
Vertical moisture barriers are used around the
perimeter of the building to cut off the source of lateral
water migration. Vertical barriers are more effective than
horizontal barriers in terms of slowing the rate of heave
and causing the water content distribution to be more
uniform below the structure. Polyethylene membrane and
concrete can be used as vertical barriers. When such
materials are used as a barrier, this depth should be equal
to or greater than the depth of moisture fluctuation [4].
2.3.2 Adequate Drainage
To control water fluctuation, adequate drainage system for
surface and subsurface water is essential. Drainage is
provided by surface grading and subsurface drains. The
most commonly used technique is grading of a positive
slope away from the structure. The slope should be
adequate to promote rapid runoff and to avoid collecting
near the structure, pond water which could migrate down
the foundation soil. These slopes should be greater than
1% and preferably 5%. Covered drains can be provided to
discharge away the surface runoff water. Subsurface
drains may be used to control a rising water table,
groundwater and underground streams and surface water
penetrating through pervious soil. Subsurface drains or
perforated pipes 15 cm diameter can help to control the
water table before it rises but may not be successful in
Magdi M. E. Zumrawi et al Damages of Buildings on Expansive Soils: Diagnosis and Avoidance
111| International Journal of Multidisciplinary and Scientific Emerging Research, Vol.6, No.2 (May 2017)
lowering the water table in expansive soil, [3]. This
usually is not accomplished due to negligence, cost,
limited property size and other reasons.
2.3.3 Chemical Stabilization
Many chemical admixtures can be used to stabilize
expansive soils but lime has proven to be the most
effective for highly expansive clays. The use of lime to
prevent or minimize soil expansion has been increasing in
favor during the last few decades because it significantly
reduces swelling characteristics and increases soil
strength. Generally the amount of lime required to
stabilize expansive soils ranges from 5 to 8% by weight.
The addition of lime to clay soil provides an abundance of
calcium ions (Ca+2) and magnesium ions (Mg+2). These
ions tend to displace other common cations such as
sodium (Na+) and potassium (K+), in a process known as
cation exchange. Replacement of sodium and potassium
ions by calcium significantly reduces the plasticity of the
expansive clay, [20]. A reduction in plasticity is usually
accompanied by reduced potential for swelling. The
addition of lime increases the soil pH, which also
increases the cation exchange capacity. A change of soil
texture takes place when lime is mixed with clay. Fly ash
and fiber reinforcement in foundation also takes a vital
role for stabilization of expansive soils, [4].
2.3.4 Soil replacement
Soil replacement is the simplest methods for preventing
building damages. The most important requirements for
soil replacement are the type of the material for
replacement, the depth of replacement and the extent to
which the replacement is needed. The material replaced
should be non-expansive and impermeable, [3]. If the
replacing material is highly permeable (coarse sand,
gravels), it transmits the surface moisture directly on the
expansive clay layer. This would bring about differential
movement the same as the surface. Hence, use of sand,
gravel as replacing materials is dangerous. The depth at
which the soil to be replaced depends on the depth of the
active zone. Active zone is the depth at which the soil does
not affected by dry weather, [2].
2.3.5 Structural Measures
The structural measures that should be undertaken in order
to minimize or eliminate damages of structures due to
heaving are dependent on the design of the structures. The
types of foundations commonly used worldwide to support
structural loads in expansive soil are: spread footings,
continuous footings, stiffened raft and bored concrete
piles. The shallow foundations are modified to increase the
bearing pressure so as to minimize heave. Some
modifications have been provided include, [2]:
narrowing the width of the footing base,
placing the foundation wall directly on grade without
a footing,
providing void spaces within the supporting beam or
wall to concentrate loads at isolated points, and
increasing the reinforcement around the perimeter
and into the floor slab to stiffen the foundation
3. Research Methodology
The research methodology which has been followed to
achieve the ultimate goal of the study is conducted by field
and laboratory investigation. Some cases of existing
houses in Khartoum state were selected to assess their
damages. The case study was carefully selected to provide
rich information on expansive soils problems to
lightweight buildings. The research focused on evaluating
damages that occurred on some houses in Khartoum state
in order to come out with the possible causes and practical
remedies. Primarily the study based on recorded
information, field investigation and laboratory tests.
3.1 Project Description
Khartoum is the capital and largest city of Sudan.
Khartoum state is composed of three towns, Khartoum;
Khartoum North; and Omdurman. The three towns are
located around the river Nile and its two main branches,
Blue Nile and White Nile in a triangle shape. Recently,
construction developments are concentrated in areas
extensively covered with expansive soils. The study area
in this work includes most regions of Khartoum state
where expansive soils are dominantly found, namely
Almenshia in Khartoum (KH), Shambat and Alshabia in
Khartoum North (KN) and Alarda in Omdurman (OM),
shown in Figure 2.
Figure 2 The project location in Khartoum state
In Khartoum state, most of the residential buildings are
low rise buildings which are susceptible to damage caused
by expansive soils. These buildings are mainly constructed
from hollow concrete blocks, brick or masonry walls.
Only few buildings are high rise or tall buildings. Most of
the dwellings of Khartoum, particularly in expansive soil
areas have similarities in size, construction material and
construction method. Taking samples from the population
inference can be made about the buildings those
constructed in expansive soil areas.
Ten randomly selected houses in the three towns of
Khartoum state. The houses are located at Almanshia
(three houses) in Khartoum; Shambat (three houses) and
Alshabia (two houses) in Khartoum North; and Alarda
OM
KH
Magdi M. E. Zumrawi et al Damages of Buildings on Expansive Soils: Diagnosis and Avoidance
112| International Journal of Multidisciplinary and Scientific Emerging Research, Vol.6, No.2 (May 2017)
(two houses) in Omdurman. The selected houses for the
study were built in relatively small areas about 300 to 400
m2. Most of the studied houses (seven houses) are single
storey buildings while the remaining are two-storey
buildings. The houses are mostly built using masonry or
hollow block concrete for load bearing walls or partition
walls of reinforced concrete frame. The buildings are
supported on reinforced concrete pad or strip foundations.
3.2. Records Review
A detailed record Review was conducted to obtain some
information about the design and construction of the
project. The documents contain information data about the
building history, structural design, construction materials
information and specifications, previous maintenance
records, and other relevant information such as soil
investigation reports, and temperature, weather or rainfall
data. These collected data are very important for both the
field survey task and the evaluation of building failures.
3.3 Field Investigation
The field investigation program includes site visits to the
ten houses locations, interviews and structured
questionnaire to have more information. A considerable
amount of time was devoted to an arranged number of site
visits in the case study sites to ascertain the visible
prevailing conditions. To back up the site visits, visual
inspections and studies of construction details of the
buildings were carried out. The aim of visual inspections
was to observe different factors affecting the foundation
structures, identify construction type and materials, defects
and signs of movement. Indicators of soil movement such
as diagonal cracks in the walls, sticking doors and
windows and cracks in the floors were identified. In
addition, representative soil samples were collected from
pitholes that excavated in each site.
3.3.1 Site Reconnaissance
The field investigation started with the site reconnaissance
in order to collect information about the house
construction and how the failure occurred from the owners
to assess in investigating the source and reasons of
failures. For each selected house the required data was
first collected by conducting physical observation. This
task has the following three major components: (i)
Identifying construction material of each component of the
building, (ii) Careful observation and analysis of extent of
damage in each building element, and (iii) Studying surface
drainage and ground water table conditions. The second task
was interviewing house owners or contractors who had
been participating in construction of buildings or people
directly involved during the construction period.
3.3.2 Inspection of Distresses
A visual inspection was conducted for each house in order
to examine the extent of damage, identify possible causes
and evaluate the structural defects in the superstructure
members. A questioner was prepared so that properly
organized and consistent data could be collected during
assessment of the selected houses.
It was observed that most of the surveyed houses of single
storey buildings of masonry or hollow block concrete load
bearing walls and supported on strip foundation, suffered
much damages than the two-story buildings that supported
on reinforced concrete pad foundations. One possible
explanation for this could lie in the fact that the single
storey buildings which exert downward pressures lower
than the amount of upward ground pressure exerted by the
swell soils.
The most common exterior damage was to the fence
walls. Most of the surveyed houses, the fence walls are
supported on strip foundation at a shallow depth. It was
clearly observed that the walls nearby gardens are much
suffered serious cracks due to the adverse effect of garden
watering, shown in Figures 3 and 4. Cracks were vertical,
horizontal or diagonal, and almost always through the
mortar joints between bricks. Cracking were from hairline
to more than 20 mm in width. In some cases the whole
wall was separated, as shown in Figure 4.
Figure 3 Sever vertical cracks appeared at the joint
between column and masonry wall of the fence
Figure 4 Severe and deep cracks appear in the exterior
walls of the building
The roots of big trees grown adjacent to the building
resulted in settlement of the foundation wall around the
corner of the building as shown in Figure 5. Also severe
Magdi M. E. Zumrawi et al Damages of Buildings on Expansive Soils: Diagnosis and Avoidance
113| International Journal of Multidisciplinary and Scientific Emerging Research, Vol.6, No.2 (May 2017)
cracks and damages were seen in the exterior walls of the
building due to water leakage in wastewater pipes
occurred at the front part of the building and near bath
rooms.
Figure 5 Foundation wall partially settled around the
corner due to trees nearby the building
The building internal walls as well as floors much suffered
from serious cracks. It was observed that the cracks are
generally diagonal at approximately 45° occurred above
and below windows and above doorways. Movement of
the walls had distorted door and window frames. The
major type of damage observed in the houses is severe
cracks around corners of doors and windows and reduction
in wall height due to sinking of foundation. However; the
extent of damage in the internal walls ranges from minor
to severe cracks in different direction as shown in Figure
6.
Figure 6 Serious cracks around window in the interior
wall
Floor damage caused by expansive soils is evident in most
houses, shown in Figures 7 and 8. In these figures, it was
observed that floor heave caused uneven level of the
ceramic tiles and serious cracks appear on the slab. The
floor heave resulted in difficulty in opening doors and
windows as clearly seen in Figure 9.
Figure 7 Floor heave resulted in considerable difference in
level about 5.5 cm
Figure 8 Heaving of interior floor causing cracking of slab
Figure 9 Doors not properly close or open due to
movement of floor
Damage to concrete perimeter foundations caused by
differential heave of the foundation soil ranged from
minor hairline and 1 to 2mm cracking to much larger
cracks with anywhere from 50-100 mm of separation and
significant lateral offsets, as shown in Figure 10.
Magdi M. E. Zumrawi et al Damages of Buildings on Expansive Soils: Diagnosis and Avoidance
114| International Journal of Multidisciplinary and Scientific Emerging Research, Vol.6, No.2 (May 2017)
Figure 10 Severe cracking in concrete perimeter wall
showing exposed reinforcing
3.4 Experimental Work
To investigate the causes of failures occurred in the
studied houses, laboratory testing was carried out. For
each building, an open pithole of 2m depth was excavated
in the vicinity of the building. The pits were excavated
manually using pick-axes and shovels. Disturbed soil
samples were collected, packaged and transported to the
laboratory of soil mechanics in university of Khartoum.
Physical and index properties, and swelling
characteristics were determined on the soils by following
relevant procedures. The test results are given in Table 2.
The foundation soil is classified as high plastic clay of
high expansiveness.
Table 2 Geotechnical properties of soils tested
Soil Property
Location of Soil Sample
Almanshya
Shambat
Elshabia
Alarda
Clay Content, %
(<2µ)
65
69
58
46
Liquid limit, %
79
87
75
57
Plastic limit, %
20
24
28
19
Plasticity index, %
59
63
47
38
Free swell index, %
190
220
180
90
Swell Pressure, kPa
72
95
64
55
Degree of
expansion
High
Very High
High
Moderate
Soil classification
CH
CH
CH
CH
4. Results and Discussion
Based on the field survey and soil investigation as well as
thorough study of relevant documents such as working
drawings and drainage patterns of the area, the following
study findings were presented and discussed in the coming
paragraphs.
4.1 Observations and Comments
The exterior walls of fences, masonry or hollow concrete
blocks walls of 30 cm thick suffered extensive cracking
due to differential heave. Most of these walls are located
adjacent to gardens of big trees. The garden watering is the
main cause of soil heave that created uplift pressures
greater than the walls weights leading to wall movements
and severe cracking.
The field work and laboratory tests have shown soil
profiles of the studied houses. Tested soil samples from
the project sites have been found to meet the diagnostic
criteria for expansive soils. Laboratory tests of the clay-
sized fraction, liquid limits, plasticity index, and swell
reflect expansive potential due to the presence of clay
minerals. From Table 2, the samples have liquid limits in
the range 57% to 79%, plasticity index 38% to 59%, clay
content (fracture >2µ) 46% to 69% and free swell 90% to
220%. It is observed that the soil obtained from Shambat
has very high expansion while Alarda soil shows moderate
expansion. The most expansive stratum is located at the
depth of about 1 meter from the ground which is thought
to be the active zone. The soils in Khartoum state can put
forth upward swell pressure of about 45 kPa, which is
greater than the average downward pressure of about
40kPa exerted by most of the single-storey buildings.
It was found that a considerable number of lightweight
buildings are built so cheaply by low income urban
dwellers with inadequate sources of finance, thus resulting
into damages whose repair may be not possible or cost
effective and replacement was the only viable option.
Many of the structural problems originate from
improper design or construction, insufficient foundations
and weak or inadequate materials triggered by the swelling
soils. Other factors influencing the degree of damages
include the climatic conditions, age, poor drainage and wet
spots around the foundations, and neglected maintenance
of the buildings. Taken together these factors underlying
building damages are not mutually exclusive. The main
challenge for any inspector is to investigate technically
which one of these is predominant in any particular case.
4.2 Possible Causes of Damages
Based on the study results and available literature, the
main causes of damages or failures in buildings founded
on expansive soil areas are attributed to some factors such
as climatic changes, poor drainage, presence of gardens
nearby buildings, damaged water pipes and improper
foundation design.
4.2.1 Climatic changes
Seasonal changes in rainfall were the principal cause of
the change of soil moisture. This led to downward
movement during summer and upward movement during
winter. The consequent rising and settling of ground
surface occurred in the dry and wet seasons resulting in
seasonal subsidence and seasonal recovery respectively.
The study results and observations indicated that
expansive soils which experienced periodic swelling and
shrinkage during alternate wet and dry seasons caused
considerable damage to structures founded on them. The
damage to structures built on expansive soil in wet
climates usually occurred during drought period and
damage to structure built on dry climate occurred during
rainy season.
Magdi M. E. Zumrawi et al Damages of Buildings on Expansive Soils: Diagnosis and Avoidance
115| International Journal of Multidisciplinary and Scientific Emerging Research, Vol.6, No.2 (May 2017)
4.2.2 Poor drainage
Improper drainage is probably the most important factor
contributing to soil volume change and subsequent
damage to buildings. If water is allowed to stand in
drainage ditches close to buildings, it can penetrate down
and amplify heave, [4]. The main causes of poor surface
drainage can be considered include: surface runoff not
properly drained away from the building; sprinkling of
water for grass and shrub plantation; overflow from
elevated and/or ground water tank; and slope of
surrounding area.
4.2.3 Presence of gardens nearby buildings
Existence of lawns and gardens with fast growing trees in
the vicinity of the building may cause cracks in walls due
to expansive action of roots growing under the foundation.
Roots of some trees generally spread horizontally on all
sides in the effective zone of the foundation soil when
trees are located close to a building, [19].
Trees absorb water from the nearby foundation soil
through their root system and cause shrinkage of soil
especially during the dry season when moisture available
for roots to suck is the least. This is the reason why big
trees should not be located within a distance of 0.5 to 1
times their mature height from the structure. To minimize
the effect of big trees roots, moisture barriers should be
put in place to cover the effective zone of foundation soil,
[19].
4.2.4 Damaged water pipes
Shallow water pipes buried in the zone of seasonal
moisture fluctuation, are exposed to enormous stresses by
shrinking soils. If water or sewage pipes break, then the
resultant leaking moisture can aggravate swelling damage
to nearby structures. The effect of a leaking water line is
dependent on the soil moisture condition in the supporting
expansive soil mass prior to the leaking occurrence.
Dishing of floor systems due to clay heave under the
foundations could occur when excessive water is present
due to site leakage at the edges of the structure, [1].
4.2.5 Improper foundation design
Assessment of foundation design sheets and reports
showed that there no any consideration for checking the
safety of building against uplift pressures. This indicates
that there is either a knowledge gap or carelessness in
design offices and/or designers. The authority who is in
charge for approval of these designs also doesn‟t demand
such requirements. Even design documents are not
required for building below two stories which are
vulnerable for damage due to their light weights. Problems
created by expansive soil heave can be properly addressed
by considering the situation during the design phase and
providing detail drawings for house builders.
4.2.6 Construction with low quality materials
The use of low quality materials for construction adversely
affects the performance of the building. This sometimes
occurs in the form of the improper concrete mixture, and
poor foundation of low bearing capacity. The use of
substandard materials for building construction and wall
plastering will affect structural performance. These
materials may accelerate deterioration of the building and
often result in cracking, low strength, shortened service
life, or some combination of these problems. Designers
have come to rely on modern structural materials.
However, manufacturing or fabrication defects may exist
in the most reliable structural materials, such as standard
structural steel sections or centrally mixed concrete.
Conclusion
This study has been undertaken to investigate the causes of
building damage. The findings and conclusions drawn as
follows:
The buildings in the case study area exhibit high
variations in type and quality of construction ranging
from cheap traditional materials to modern imported
ones. While the effects of expansive soils
predominate in the lightweight buildings. Light
damages were observed in multi-storey buildings
because they are to some extent constructed of sound
materials heavy enough to prevent swelling pressures
and their foundations are beyond the active zone.
All the tested soils satisfied the expansive soil criteria
and have potential expansion rating from moderate
to „very high‟. The soils contain swelling clay
content more than 30%, have plasticity index
exceeding 30%, free swell more than 90%, and
swelling pressure in excess of 55kPa, which is
greater than the pressure exerted by most of the
lightweight footings almost 45kPa.
The experience of constructing buildings in
Khartoum state without appropriate measures or with
underestimation of the design and construction on
swelling soils has led to damages of the structures.
This study has helped identify the expansive soils
and associated problems in buildings. It provides
some mitigation measures to prevent structural
damages originating from the behaviour of expansive
soils.
It was pointed that understanding the causes of
building damage will significantly contribute to the
proper selection of effective repair technique results
in prolonged service life of buildings and significant
savings for the owners.
The experience of the investigator is an important
factor in correctly diagnosing the building failure
causes and determining the best repair technique.
The study has the potential to improve the safety of
the communities by assisting homeowners in
promoting proper design, positive construction and
maintenance altitudes.
Magdi M. E. Zumrawi et al Damages of Buildings on Expansive Soils: Diagnosis and Avoidance
116| International Journal of Multidisciplinary and Scientific Emerging Research, Vol.6, No.2 (May 2017)
Most of the damages caused by expansive soils are
due to poor construction and lack of timely
maintenance by the homeowners and are in most
cases preventable, yet the communities have
insufficient knowledge about the features and
behaviour of the expansive soils.
References
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[3]. Chen, F. H. (1975): Foundations on expansive soils, First
Edit. Chen and Associates, Consulting Soil Engineers,
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[7]. Jones, D. E. and Holtz, W. G. (1973): “Expansive soils – the
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avoidance, E. and FN Spon LTD, New York.
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[18]. Boscardin, M. D. and Cording, E. J. (1989): “Building
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Expansive Soil Stabilized with Calcium Chloride,” World
Academy of Science, Engineering and Technology
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10, No. 2, pp. 199203.
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In recent years building failures and the resulting lawsuits and awards for damages have frequently been in the news. The biggest headlines may have been reserved for structural failures and complete collapses, but we should not forget the less newsworthy failures such as leaky roofs, damp walls, dropped foundations and rotted timber. This book gives practical guidance on the prevention of failure by describing the nature and cause of the most common defects in buildings, and then shows how they should be avoided in design and construction.
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Analytic models and field data are used to develop procedures to evaluate the tolerance of brick-bearing-wall and small frame structures to the ground displacements that develop during opencutting and tunneling. The role of horizontal and vertical ground displacements are discussed and the effects of grade beams, building orientation and building location relative to excavation are examined. Case studies of structures adjacent to opencuts and tunnels are used to verify procedures for estimating potential for structures adjacent to excavations to sustain damage.
Foundations on expansive soils, First Edit. Chen and Associates, Consulting Soil Engineers
  • F H Chen
Chen, F. H. (1975): Foundations on expansive soils, First Edit. Chen and Associates, Consulting Soil Engineers, Denver, Colo., U.S.A.