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Challenging Problems of Gypseous Soils in Iraq
Des problèmes difficiles des sols gypseux en Irak
Al- Saoudi N.K.S.
University of Technology-Baghdad-Iraq
Al- Khafaji A.N., Al- Mosawi M.J.
University of Baghdad – Baghdad- Iraq
ABSTRACT: Gypseous soils are classified as one of the problematic soils due to their complex and unpredictable behaviour.
They exist in many parts of the world, concentrated mainly in arid and semi-arid regions. In Iraq gypseous soils cover about 20 to
30 % of its total area concentrated primarily on the west desert and extended to the southern parts and directed towards south
west. Gypsum soils experience sudden collapse upon exposure to water, losses of serviceability of many structures were observed
in different parts of Iraq. Extensive research was made in Iraq to investigate and understand the behavior of Gypsum soils and to
set safety limits for the collapse and suggest practical precautions during construction. The enormous amount of data collected
from different research sources revealed wide spectrum of information covering the overall performance of Gypsum soils under
different environmental and climate conditions The present paper focuses on the main geotechnical properties of gypseous soils
and their effect on the collapsible mode of failure, some practical solutions are also proposed that provide safety precautions
RÉSUMÉ : Les sols gypseux sont classés comme des sols problématiques à cause de leurs comportements complexes et imprévi-
sibles. Ils existent dans plusieurs régions du monde, principalement dans des régions aride et semi-aride. En Irak, les sols gypseux
couvrent entre 20 et 30 % du pays et sont principalement concentrés dans le dessert de l’ouest et s’étendent vers les régions du sud
et orientées vers le sud-ouest. Les sols gypseux s’effondrent soudainement lorsqu’ils sont soumis à l’eau et beaucoup de structures
inutilisables ont été observées dans différentes zones en Irak. Des recherches approfondies ont été menées en Irak pour étudier et
comprendre le comportement des sols gypseux afin de déterminer les limites avant l’effondrement et de suggérer des précautions
concrètes lors de la construction. L’énorme quantité de données recueillies auprès de différentes sources a révélé un large spectre
d’informations couvrant l’ensemble des performances des sols gypseux sous différentes conditions environnementales et climati-
ques. Le présent document se concentre sur les principales propriétés géotechniques des sols gypseux et sur leurs effets sur les
écroulements de structure, enfin quelques solutions pratiques sont aussi développées pour proposer des mesures de sécurité.
KEYWORDS: Gypsum,collapsibility, Gypseous Soils, Problematic Soils
1. INTRODUCTION
Gypseous soils are one of the most complex materials that
challange the geotechnical engineers. Structures or dams
founded on gypseous soil may experience unpredictible defor-
mations that ultimatley may cause catostrophic failure. In iraq it
has been reported that several structures have experienced dif-
ferent patterns of cracks and uneven deformations generated
primearly from the exposion of the supporting gypseous soils to
water. It is a well known fact that gypseous soils demonstrate
high bearing capacity and very low compressibility when they
are in the dry state. On the contrary a sudden collapsibile behav-
iour was reported when the gypseous soils are exposed to wa-
ter.The collapsibility of gypseous soils results from the direct
contact of water. The dissolution of different types of salts con-
tained inside the mass of gypseous soil will generate new pores
inside the soil skeleton and loosen the cementing bonds between
the particles. This process creates a meta stable structure that fa-
cilitates the sliding of particles into a more dense state. The rate
of dissolution of gypsum depends primarily on environmental
changes in moisture content generating from fluctuation of
ground water table and /or surface water, climate changes typi-
cally temperature, permeability and state of flow conditions in
addition to the type and content of gypsum.
During the last three decads many attempts were made in
Iraq through intensive research programs set in many institution
to investigate and underestand the behaviour of gypseous soils
under various enviromental and loading conditions. The first ob-
jective of these research programs was to determine the physical
proerties of the gypseous soils and to check whether staandard
tests can be used and if not what modifications are required. Fol-
lowing that several attempts were made to determine the geo-
technical properties such as compressibility, collapsibility and
shear strength parameters under various flow and environmental
conditions and loading conditions. The tests were performed us-
ing triaxial and Rowe cells allowing soaking and leaching of the
soil samples. Plate load tests were also performed under differ-
ent soaking periods to moniter the generated deformation with
time. Numerical techniques were also used to simulate the diso-
lution process of gypsum under soaking and leaching conditions.
The abundant amount of data obtained from the lengthy re-
search programs revealed in many cases contradicting results
due to the complexity of the gypseous soils. So no regid conclu-
sions are yet been drawn.
The paper sheds the light on the distribution of gypsum in
Iraq. A summary of main physical and geotechnical properties
with emphises on the collapsibility is presented and a some re-
midied are proposed.
