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A simple approach for predicting vertical movements of expansive soils using the
mechanics of unsaturated soils
Une approche simple pour prédire les mouvements verticaux des sols gonflants par la mécanique
des sols non saturés
Adem H.H., Vanapalli S.K.
Civil Engineering Department, University of Ottawa
ABSTRACT: The vertical soil movements associated with environmental changes which include climate, vegetation, watering of
lawn and soil cover type for a test site with an expansive soil deposit in Regina, Canada were predicted by Ito and Hu (2011) using a
combination of soil-atmosphere and soil-displacement models for a period of one year. In this paper, vertical soil movements of the
same site were estimated reasonably well considering soil suction changes and associated modulus of elasticity as key parameters in
a volume change constitutive relationship that is based on the mechanics of unsaturated soils. The proposed method is referred to as
the modulus of elasticity based method (MEBM). The MEBM has been also evaluated earlier for three other case studies with
satisfactory results. The results of the study presented in this paper and the other three case studies that were reported in the literature
are encouraging for extending the simple MEBM in engineering practice for rational design purposes of both the sub and
superstructures constructed in or on expansive soils.
RÉSUMÉ: Les mouvements verticaux des sols associés aux changements environnementaux qui comprennent le climat, la
végétation, l'arrosage de la pelouse et le type de couverture du sol pour un site d'essai avec un dépôt de sol gonflant à Regina, Canada
ont été prédits par Ito et Hu (2011) en utilisant une combinaison de modèles sol-atmosphère et de déplacement du sol pour une
période d'un an. Dans cet article, les mouvements de sol verticaux sur le même site ont été estimés raisonnablement bien en tenant
compte de la succion dans le sol et du module d'élasticité associés comme paramètres clés pour une relation constitutive du
changement de volume qui est basée sur la mécanique des sols non saturés. La méthode proposée est appelée méthode basée sur le
module d'élasticité (MBME). La MBME a également été évaluée précédemment pour trois autres études de cas avec des résultats
satisfaisants. Les résultats de l'étude présentée dans ce document ainsi que les trois autres études de cas qui ont été rapportés dans la
littérature sont encourageants pour l'application de la MBME pour la conception rationnelle tant des substructures que des
superstructures construites dans ou sur les sols gonflants.
KEYWORDS: unsaturated expansive soils, vertical movement, suction, modulus of elasticity, vegetation, climate.
1 INTRODUCTION
Expansive soils shrink and swell in response to alternate dry and
wet conditions inducing vertical soil movements. These soil
movements cause significant damage to the lightly loaded
engineered structures and contribute to economic losses which
are greater than all natural disasters combined (Jones and Holtz
1973). The behavior of expansive soils associated with
environmental changes hence should be considered when
designing buildings, pavements, foundations (shallow and
deep), pipelines, retaining walls, earth dams, canal or reservoir
linings, and other structures that are constructed in or on
expansive soils.
Different methods for predicting the volume change
behaviour of expansive soils have been proposed in the
literature. However, most of the available methods focused on
predicting the maximum potential heave at saturation condition.
Furthermore, these methods or studies were limited to
expansive soils of local regions that cannot be extended
universally. Recently, Vanapalli and Adem (2012, 2013), and
Adem and Vanapalli (2013) presented and assessed a simple
approach for estimating the vertical soil movements of different
expansive soils for overcoming these limitations. In this
approach, the volume change constitutive relationship
developed by Fredlund and Morgenstern (1976) for unsaturated
soils was integrated along with the soil-atmosphere model
VADOSE/W (Geo-Slope 2007). The analyses of the results
demonstrated that the proposed approach, which has been
referred to as the Modulus of Elasticity Based Method
(MEBM), was capable of reproducing the vertical movement of
expansive soils over time in response to the net changes in soil
suction within the active zone for three different case studies
(Vanapalli and Adem 2012, 2013, and Adem and Vanapalli
2013).
The objective of the present study is to check the validity of
the MEBM for an additional test site with an expansive soil
deposit in Regina, Saskatchewan, Canada. This site was
originally modeled and presented by Ito and Hu (2011). These
investigators simulated the Regina expansive clay vertical
movements based on the suction data predicted from the soil-
atmosphere coupled model
by applying one year’s climate data
(from 1 May, 2009 to 30 April, 2010). The liquid limit and
plastic index values of Regina clay vary from 70 to 94% and
from 40 to 65%, respectively. The soil properties required
include the soil water characteristic curve (SWCC) and the
coefficient of permeability function along with the climate and
vegetation data as input for the soil-atmosphere model. The
vertical movements of this soil with respect to the changes in
suction values were predicted using the soil-displacement
model. A general purpose partial differential equation solver
(FlexPDE) was used as a tool to solve the governing partial
differential equations in the modelling process. Various factors
that influence the soil movements such as the climate,
vegetation, watering of lawn and soil cover type were
considered in the modelling.
In this paper, estimated values of soil suction, volumetric
water content and vertical movements of expansive soils at
different depths obtained from the MEBM were compared with
the published results of Ito and Hu (2011).
Due to limitations of
space, only the
results of soil suctions and vertical movements
have been presented and discussed in this paper, in addition to
providing comparisons with the results of
Ito and Hu (2011)
.
There is a good comparison between the results from both the
studies.
