1. 11/30/2016
CIVIL, ENVIRONMENTAL AND SUSTAINABLE ENGINEERING
SCHOOL OF SUSTAINABLE ENGINEERING AND THE BUILT ENVIRONMENT
CEE553 – ADVANCED SOIL MECHANICS
FALL 2016
FINAL PROPOSAL ON “DESIGN OF
FOUNDATIONS ON COLLAPSIBLE
SOILS”
BHARATH GUMMARAJ
ASU ID - 1209909997

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CONTENTS
1. PROBLEM DESCRIPTION ................................................................................................... 2
1.1 INTRODUCTION............................................................................................................ 2
1.2 NEED AND IMPORTANCE........................................................................................... 2
2. OBJECTIVES.......................................................................................................................... 3
3. LITERATURE REVIEW ........................................................................................................ 3
4. INFORMATION FROM LITERATURE ............................................................................... 5
5. PLAN OF WORK.................................................................................................................... 8
6. BUDGET............................................................................................................................... 10
7. SCHEDULE .......................................................................................................................... 11
8. PERSONAL STATEMENT.................................................................................................. 11
9. REFERENCES ...................................................................................................................... 11

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1. PROBLEM DESCRIPTION
1.1 INTRODUCTION
Soils which are dry and strong in their natural state, but weakens and loses its density when
saturated are termed as collapsible soils. As its name suggests collapsible soils loses strength upon
wetting and collapses. Geotechnical Engineers define collapsible soils as “Soils that settle due to
self-weight upon wetting”. [4]
Collapsible soils are called metastable soils, and the process through which it collapses is often
termed as Hydro compression, Hydro consolidation or Hydro collapse. [1]
The mechanism of collapse can be explained as a simple example of Cornflakes that we have for
breakfast. When poured in a bowl it appears to be strong and stiff, but becomes weak and soft once
we add milk to it.
Collapsible soils consist of sand and silt particles that are arranged in a honeycomb structure held
together by cementious materials such as clay or calcium carbonate, which are strong in their dry
state. But upon wetting bonding materials dissolves in water breaking geometry. Hence soil
collapses. The type of water soluble bonding material depends upon origin of collapsible soils.
1.2 NEED AND IMPORTANCE
Collapsible soils are often encountered in Arid and Semi-Arid regions. To naked eye these soils
appear to be very strong and people are often mistaken by its properties in dry state. These soils
show collapse potential only upon wetting. Hence it is important to know properties of soil in its
wet state also. If not detected, then upon future wetting of soil the foundations undergo total and
differential settlements, which may lead to collapse of structure.
To avoid these kind of differential settlements, it is very important for foundations Engineer to
identify collapsible soils and to provide necessary mitigation measures.

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2. OBJECTIVES
 To find Origin and Occurrence of collapsible soil deposits.
 To identify collapsible soils based on its occurrence.
 To determine source of wetting. i.e., to identify source of water which triggered or may
trigger the process of collapse.
 To list suitable sampling and testing techniques based on origin of soils.
 To determine settlement at site, to know the extent of damage and to determine water
boundary below ground.
 To propose suitable remedial measures based upon source causing wetting of soil.
3. LITERATURE REVIEW
Donald P. Coduto, in his book on Foundation Design, [1] classifies collapsible soils as alluvial
soils (soils deposited by flowing water), Aeolian Soils (soils deposited by wind), Colluvial Soils
(soils deposited due to gravity) and residual Soils (soils deposited due to weathering of rocks).
He explains that, soils which does not contain too much gravel can be effectively sampled at site.
Whereas lightly cemented soils are difficult to sample and gravelly soils are extremely difficult to
sample. Hence for gravelly soils in-situ tests are preferred over laboratory testing.
Double oedometer test or single oedometer tests can be used to determine collapse potential of
soils in laboratory as a function of overburden stress. In field testing, soils are usually wetted by
external means before testing. However, they are not wetted to 100% saturation. But are typically
wetted to about 50-80% saturation.
The settlement depends on depth of wetting, hence it is difficult to estimate collapse potential at
site. Since, assuming depth of wetting in advance is difficult. In laboratory tests, collapse potential
of soil deposit is estimated by extrapolating obtained results for sample by making necessary
corrections for overburden stress and degree of saturation.
Sandra L. Houston, William N. Houston, Claudia E. Zapata and Chris Lawrence, in their
technical paper on Geotechnical Engineering Practice for Collapsible soils, [2] explains that, since
natural processes such as water flow, wind flow or gravity is accounting for deposits of collapsible

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soils. The geologic, geographic and geomorphologic information can be very helpful in locating
collapsible soil deposits.
They explain that, volume change upon wetting is either swell if material is plastic, initially dry
and lightly confined or collapse if material is non-plastic or slightly plastic, initially dry and heavily
confined.
Collapsible soils are not confined to arid and semi-arid regions and have been encountered in other
parts of the world also. Liquefaction and dynamic settlement potential of these soils are masked
during site investigation due to high dry strength, which usually results in high SPT N-values.
Several mitigation measures are available to avoid collapse. But, best method is selected based on
timing of mitigation, source of loading, source of wetting and cost.
Claudia E. Zapata, in her presentation on Introduction to collapsible soils [3] explain that Unit
weight should be the first measure to identify collapsible soils. They have a low unit weight of
about 70-90 pcf. It is the easiest way of detecting collapse potential of soil.
Collapse potential of soils can be detected by indirect measurements like index properties, but
these are often misleading due to high strength of soils in their dry state. Best option is to perform
laboratory or in-situ tests. If remolded samples are used in laboratory, then it is necessary to bring
the samples to in-situ density and water content.
John C. Lommler and Paola Bandini, in their technical paper on Characterization of collapsible
soils [4] describes about characteristics of collapsible soils in Albuquerque, New Mexico area.
“Pin holes” were found in samples collected from Montessa park, Authors explain about the nature
and shape of these holes by studying their microscopic images.
They also explain how sample disturbances affect prediction of collapse potential and how it
affects the laboratory test results. By studying the microscopic images of soil samples they also
explain the structure of highly collapsible soils that allows them to have dry unit weight less than
what can be achieved in the laboratory.
Victor A. Rinaldi, Ricardo J. Rocca and Marcelo E. Zeballos, in their technical paper on
Geotechnical Characterization and Behavior of Argentinean Collapsible Loess [5] explain about

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the Loess formation (Aeolian Soil deposits) in Argentina which is the largest windblown deposit
in the southern hemisphere.
Loess deposits are made of fine sand and volcanic silt particles held together by unsaturated clay
buttresses, soluble salts and some less soluble cementing agents.
In this paper the authors give cumulative review of fundamental aspects related to physical
properties and engineering behavior of loess. They also explain about stress-strain behavior of
undisturbed loess specimen, electrical properties and geotechnical solutions adopted in
engineering practice in design of foundations on Loess.
4. INFORMATION FROM LITERATURE
The soil structure of collapsible soils is as shown in the figure.
Fig. 1 Collapsible soil structure [1]
Soil particles are held together by water soluble cementing agents, which upon wetting dissolves
in water, leading to collapse.
Collapsible are broadly classified based on its occurrence as alluvial soils (soils deposited by
flowing water), Aeolian Soils (soils deposited by wind), Colluvial Soils (soils deposited due to
gravity) and residual Soils (soils deposited due to weathering of rocks).
Alluvial and Colluvial soils are often found in Southwestern United states and places where similar
temperature conditions exist. In these regions evaporation is more than precipitation. Sudden
downpour initiates soil flows which reaches its destination and settles. Evaporation draws capillary
water out from the pores. This water brings soluble salts along with it and these salts settle at the

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surface. Which binds the soil particles together in the form of honeycomb structure. The process
continues and large deposits of soils are formed. These soil deposits are often found as layers of
collapsible and non-collapsible soils. It is usually found in 1 to 3m below ground. But sometimes
may extend up to 60m.
Aeolian soils are found in United states, Central Europe, China, Australia, Russia, India and
Argentina. Loess is most commonly found Aeolian soil.
Argentinian loess consists of volcanic glass minerals as major component of sand and silt particles.
When gypsum and iron oxides are present, the soil is very stable even in presence of water. Loess
is alkaline in nature with Ph.>8. In the unified classification system, it is classified as ML or CL-
ML. Dry unit weight ranges from 70-90 pcf and specific gravity is around 2.65. the natural water
content varies with depth from about 12-15% at surface to over 25% at a depth of 60ft. [5]
Large amount of cementing agents deposited at particle contact in loess can increase shear strength
of soils significantly, to an extent that soil behave as sedimentary rock. Contact level cementation,
suction forces and electrical forces all contribute to the strength and stiffness of loess.
Residual soils involve decomposition of rock minerals into clay minerals that are removed through
leaching, leading to formation of honeycomb structure with high void ratio. Residual granites in
South Africa often collapse upon wetting leading to 7-10% increase in density. [1] Results often
showed that residual soils show zero consolidation when dry and loaded to 14000psf, yet collapses
by about 10% when wetted. Because of presence of rock minerals, residual soils are strongest
collapsible soils when loaded dry, and it is very difficult to predict collapse potential of residual
soils.
To detect collapse potential of soils it is important to know the source through which soil is being
wetted. Water infiltration may be because of natural source or from artificial source. Increase in
level of ground water is the most commonly found natural source through which soil is saturated.
But, ground water level rises because of infiltration from either rainfall or through artificial means.
Some of the artificial means by which level of ground water rises are –
 Infiltration from irrigation of landscaping or crops.
 Leakage from lined and unlined canals.
 Leakage from pipelines and storage tanks.

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 Leakage from swimming pools.
 Leakage from reservoirs.
 Leakage from septic tank leach fields.
As water penetrates inti the ground, a wetting front is formed. The distance at which this is formed
depends on duration of inflow and also hydraulic conductivity of soil, which are difficult to
measure. Hence this is the greatest uncertainty in estimating collapse potential of soils.
Direct or indirect testing can be performed for detecting collapse potential of soils. Indirect
methods involve determination of index properties of soil, which will not indicate true collapse
potential of soils because soils show contrasting properties when tested under dry and wet
conditions. Hence, direct methods are preferred over indirect testing.
Direct testing involves laboratory testing or in-situ testing. Single oedometer test or double
oedometer test can be performed in laboratory to determine collapse potential of soil specimen.
Field plate load tests are performed at site by wetting the soil. [2] In-situ tests are expensive
compared to laboratory tests but has the advantage of testing more representative soil, in terms of
properties and volume. And it is also appropriate when sampling is difficult. Ex-Gravelly soils.
Once the collapse potential is identified, suitable mitigation technique need to be adopted to
prevent damage from collapse. Collapsible soils are easier to deal with since it is a one-way
collapse as compared to expansive soils, which shrinks and swells back. Best mitigation method
is to remove the entire soil layer, especially when depth of soil layer is less. Several other
mitigation methods are available, such as,
 Avoidance and minimization of wetting.
 Transfer of loads through collapsible soils to the stable soils below.
 Injection of chemical stabilizer or grout.
 Prewetting prior to construction.
 Compaction with rollers or vehicles.
 Compaction with displacement piles or by heavy tamping.
 Vibrating ground with probes equipped with water jets. (Vibroflotation)
 Controlled wetting or ground blasting combined with Prewetting.
 Design of structures to be tolerant of differential settlements.

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5. PLAN OF WORK
1) Identify presence of collapsible soils – Geologic, geographic and geomorphologic
information is helpful in identifying location of collapsible soils. Local knowledge of land
forms also helps.
2) Identify type of collapsible soil – once the location is known, it is important to know type
of collapsible soil present which helps in choosing proper sampling techniques and to
choose mitigation methods. Geologic information and local knowledge is sufficient to
determine type of soil.
3) Determine source of wetting – If the soil in site which is under study has already shown
signs of collapse, then it is important to know the source through which infiltration is taking
place. Land survey helps in identifying source of wetting.
4) Listing sampling techniques – collapsible soils can be evaluated using Direct and Indirect
methods. Indirect methods access collapse potential of soils by comparing its engineering
properties such as unit weight, Atterberg limits or clay content. Which may not be true
indicator of collapse potential of soils. Direct method involves taking samples from site
and testing it in laboratory under site conditions or performing in-situ tests such as plate
load test. In-situ tests are expensive compared to laboratory tests. Hence, for small scale
works, laboratory testing is preferred.
5) Obtaining samples from site – samples must be relatively undisturbed and representative
of soil deposit for getting effective results. However collapsible soils are often erratic in
nature and it is difficult to obtain undisturbed samples. Obtaining high quality samples
become too expensive for small scale work. Hence, it is wiser to obtain many number of
good samples rather than some high quality samples.
Engineers often use Shelby tube samples for obtaining samples. Care must be taken not to
wet the soil during sampling. Shelby tube contains thin walls which are pressed into the
ground to obtain samples. However, if soil contain gravel then thin walls of Shelby tube
are bent easily. In this situation, tube with heavier walls, such as Ring-lined barrel sampler
are used.
If the soil is gravelly in nature, then sampling becomes much more difficult. Hence, in-
situ tests are preferred.

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6) Laboratory tests to estimate settlement – Settlements are estimated as a measure of strain
that occurs upon wetting using oedometer tests. Two kinds of tests are available, Double
oedometer test and Single Oedometer test.
In double oedometer test, two identical samples are tested for consolidation parallaly. First
test is on sample at its in-situ moisture content and second test is at soaked sample. Results
are plotted together in a single graph. The difference between two curves gives potential
hydro collapse strain of the sample.
In single oedometer test only one sample is sufficient. Undisturbed sample is placed in an
oedometer and a seating load of 100psf is applied. Vertical stresses are increased till it is
higher than anticipated stress in the field. Then soil is soaked in water and resulting slump
is noted. Which gives hydro collapse strain. Once hydro consolidation is ceased, stress is
increases to allow soil to consolidate.
Single oedometer test is preferred over double oedometer test, since it simulates the wetting
sequence that occurs in the field.
Fig 2. (a) Single oedometer test results [1] (b) Double oedometer test results [1]
Obtained strain values are then correlated with standard values available to determine
collapse potential and severity of problem.

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Fig. 3 Collapse potential based on strain values form oedometer tests. [1]
7) Remedial measures – Many remedial measures are available but the best technique for a
given site is selected based upon, Timing of discovery, primary source of structural load,
depth of soil deposits, source of wetting and mitigation costs.
It is a good practice to design foundations which can resist differential settlements. But if
the structure is already in place before collapsible potential of soil is detected, the best
methods to minimize the damage are, Controlled wetting. Chemical grouting for stabilizing
soil and Underpinning.
Even though there are numerous methods available for mitigation, the method mostly
chosen by engineers is Removal and Recompaction, because of less risk involved and less
total life cycle costs.
6. BUDGET
Principal Engineer $125 per hour (Including Miles) [6]
Project Engineer $95 per hour (Including Miles) [6]
Staff Engineer $80 per hour (Including Miles) [6]
Soil Sampling $200 per sample [6]
Soil Testing $300 per sample [7]

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7. SCHEDULE
SL
NO
DESCRIPTION
DAYS
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1
Identifying presence of collapsible
soils
2 Identifying type of collapsible soil
3 Determine source of wetting
4 Listing sampling techniques
5 Obtaining samples from site
6
Performing tests to determine index
properties
7
Performing tests to determine
collapse potential
8 Listing possible remedial measures
9 Suggestions or Report
Final report may be valid up to 1 year.
8. PERSONAL STATEMENT
Bharath Gummaraj is a Master’s student, majoring in Structural Engineering in School of
Sustainable Engineering and Built Environment at Arizona State University. Bharath completed
his bachelor’s degree in Civil Engineering from Dayananda Sagar College of Engineering in
Bangalore, India. He worked as a Site Civil Engineer at Reliance Industries Limited across
various sites in Southern part of India. Currently he is pursuing his Master’s in Structural
Engineering at Arizona State University, Tempe, Arizona, U.S.A. and also working as a
Structural Engineering intern at Babbitt Nelson Engineering, Mesa, Arizona, U.S.A. His work is
oriented towards design and strengthening of concrete, steel, wood and Masonry structures. He
also holds a E.I.T (F.E) Certification from NCEES.
9. REFERENCES
[1] Donald P. Coduto, Foundation design: Principles and practices, Chapter 20, 2nd ed. United
Kingdom: Prentice-Hall, 2000.
[2] Sandra L. Houston, William N. Houston, Claudia E. Zapata and Chris Lawrence, Conference
paper on Geotechnical Engineering Practice for Collapsible soils. Arizona State University,
Tempe, Arizona -85287-5306, USA.

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[3] Claudia E. Zapata, Presentation on Introduction to collapsible soils, Arizona State University,
Advanced Soil Mechanics, Spring 2016.
[4] John C. Lommler and Paola Bandini, Conference paper on Characterization of collapsible soils,
IFCEE 2015, ASCE 2015.
[5] Victor A. Rinaldi, Ricardo J. Rocca and Marcelo E. Zeballos, Conference paper on
Geotechnical Characterization and Behavior of Argentinean Collapsible Loess.
[6] Fee Schedule for Geotechnical and Materials Testing, GEO-TECH, INC. [Online]. Available:
http://sumtercountyfl.gov/AgendaCenter/ViewFile/Item/1526?fileID=3371
[7] Summary of Laboratory fee, ENGEO, [Online]. Available: http://www.engeo.com/wp-
content/uploads/2016/06/2016-Summary-of-Lab-Fees.pdf.