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Climate Change Effects on Expansive Soil Movements
Les effets du changement climatique sur les mouvements d’un sol gonflant
Mitchell P.W.
Aurecon Australia Pty Ltd, Adelaide, Australia
School of Civil, Environmental & Mining Engineering, University of Adelaide, Australia
ABSTRACT: Climate change effects on expansive soil movements are quantified using the Thornthwaite Moisture Index (TMI). The
TMI is calculated from the moisture deficiency and surplus, both related to rainfall, and the potential evapotranspiration which is
derived from temperature. The predicted temperature increase and rainfall reduction in 2030 and 2070 are used to derive the TMI of
an area. In this way, values of TMI at present, in 2030 and 2070 are derived for Adelaide, Melbourne, Perth and Sydney. Established
relationships between TMI and the depth and magnitude of soil suction changes for sites with and without the presence of trees, and
the relationships between soil movement and soil suction changes, are used to predict the increase in soil movement for a site. A
specific example is given for Melbourne for a site without trees and with a group of trees.
It is shown that a significant increase in
predicted soil movement is expected with climate change. Therefore a continuing revision of footing design standards would be
required in order to cater for the effects of climate change
.
RÉSUMÉ : Les effets du changement climatique sur les mouvements des sols gonflants sont quantifiés utilisant l’Indice d’Humidité
de Thornthwaite (IHT). On calcule l’IHT utilisant le manque ainsi que le surplus de l’humidité, tous les deux liés au niveau des
précipitations, ainsi que l’évapotranspiration potentielle, dérivée de la température. L’augmentation prévue de la température et du
niveau des précipitations en 2030 et 2070 servent à obtenir l’IHT d’une région. De cette manière, les valeurs de l’IHT actuelles sont
obtenues pour Adelaïde, Melbourne, Perth et Sydney. Les liens établis entre l’IHT et la profondeur ainsi que l’ampleur des
changements de la pression d’eau négative des pores du sol pour des sites avec et sans la présence des arbres, et les liens entre le
mouvement du sol et les changements de la pression négative des pores du sol, sont employés afin de prévoir l’augmentation du
mouvement du sol pour un site. Un exemple spécifique est fourni pour Melbourne pour un site sans arbres mais aussi avec un groupe
d’arbres. On démontre qu’une augmentation importante du mouvement du sol est attendue avec le changement climatique. Donc, une
révision continue des normes de projet de fondations serait requise afin de préparer les effets du changement climatique.
KEYWORDS: climate change, expansive soil, Thornthwaite Moisture Index, tree effects
1 INTRODUCTION
There is considerable scientific evidence that emissions from
economic activity are causing changes to the earth’s climate
(Stern 2007). For example, in south-eastern and south-western
Australia, current predictions indicate that generally, the 2030
and 2070 temperatures are expected to increase by about 1°C
and 3°C respectively, and the 2030 and 2070 winter and spring
rainfall is predicted to decrease significantly (CSIRO 2007).
Should these predictions prove accurate, these temperature
increases and rainfall reductions are expected to cause increased
changes in soil moisture content from those at present. As well,
soil moisture changes due to trees become more adverse during
periods of hotter and drier weather, when the tree demands more
soil water than is available from rainfall. As expansive soils have
the potential for undergoing significant movement with soil
moisture changes, thus impacting on the stability of structures,
the effect of climate change on soil moisture changes needs to be
predicted so that provisions can be made to effectively respond
to the challenges of climate change when dealing with expansive
soils.
Notwithstanding that the current predictions could prove to be
inaccurate, present day geotechnical engineers are faced with the
challenge of dealing with climate change in order to cater for the
possibility that the event that the current predictions suggest,
may actually eventuate.
2 CLIMATE CHANGE PREDICTIONS
CSIRO (2007) has made predictions of climate change for
Australia, and a summary of the predictions for changes in
temperature and rainfall from present day averages for Adelaide,
Melbourne, Sydney and Perth in 2030 and 2070 is shown in
Table 1 for the emission scenarios as defined in CSIRO (2007).
Table 1: Climate Change Predictions from CSIRO (2007)
Adelaide
Melbourne
Sydney
Perth
Season 2030 2070 2030 2070 2030 2070 2030 2070
Summer +0.9 +3.0 +1.0 +3.1 +1.0 +3.1 +0.9 +2.9
Temp °C
Autumn +0.9 +2.8 +0.8 +2.7 +0.9 +3.0 +0.8 +2.7
Winter
+0.8 +2.4 +0.7 +2.2 +0.8 +2.6 +0.7 +2.3
Spring
+0.9 +3.0 +0.9 +2.9 +1.0 +3.3 +0.9 +2.9
Summer
-2
-5
-1
-4
+1
+2
-4
-12
Rainfall % Autumn
-1
-4
-2
-5
-2
-6
-4
-12
Winter
-6
-19
-4
-12
-5
-16
-7
-22
Spring
-8
-23
-7
-21
-6
-17
-9
-27
Notes on Table 1: 2030 predictions are A1B emission scenario 50
percentile; 2070 predictions are A1F1 emission
scenario 50 percentile
The predictions given in CSIRO (2007) are relative to 1990,
however in this paper they are considered to be relative to long
term average temperatures and rainfall at the present time. It can
be seen from Table 1 that generally, the 2030 and 2070
temperatures are expected to increase by about 1°C and 3°C
respectively. Table 1 also indicates that the 2030 and 2070
winter and spring rainfall is predicted to decrease significantly.
