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Characterization of geomechanical and hydraulic properties of non-wettable sands
Caractérisation des propriétés géomécaniques et hydrauliques des sables non mouillants
Kim D., Yang H.-J., Yun T.S.
Department of Civil and Environmental Engineering, Yonsei University, Yonsei-ro 50, Seoul, 120-749, Republic of Korea
Kim B., Kato S.
Department of Civil Engineering, Kobe University, Rokkodaichou 1-1, Nada-gu, Kobe, 657-8501, Japan
Seong-Wan Park S. W.
Department of Civil and Environmental Engineering, Dankook University, Suji-gu, Yongin, 448-701, Republic of Korea
ABSTRACT: Wildfire, diagenesis, and organic contamination often induce the non-wettability in soils which in turn dominate
physico-mechanical behaviours and control the contact angle and capillary pressure. This study presents the characterization of
hydraulic and geomechanical properties of non-wettable sands using artificially synthesized hydrophobic sands. The critical
hydrostatic pressure that initiates the fluid intrusion into dry hydrophobic sands is measured to estimate permeation boundary.
Hydraulic conductivity values of both hydrophilic and hydrophobic sands under fully saturated condition are examined to evaluate the
drag force effect. For geomechanical study, a series of constant water content compression tests are performed to assess the
mechanical behavior on a reconstituted specimen of unsaturated non-wettable sands. The stress-strain relationships according to the
degree of saturation under confining pressure condition are observed so as to derive the suction stresses. Results highlight that the
surface modification at nano-scale determine the spatial configuration of water phase in pore space and its impact on fluid flow and
strength with varying degree of saturation prevails.
RÉSUMÉ : Les incendies, la diagenèse et la contamination organique induisent souvent une non-mouillabilité des sols qui, à son tour,
domine leurs propriétés physico-mécaniques et contrôlent l’angle de contact et la pression capillaire. Cette étude présente la
caractérisation des propriétés hydrauliques et géomécaniques de sables non mouillants en utilisant des sables hydrophobes synthétisés
artificiellement. La pression hydrostatique critique qui déclenche l’intrusion de liquide dans les sables hydrophobes secs est mesurée
pour estimer la limite de perméation. Les valeurs de conductivité hydraulique pour des sables hydrophiles et hydrophobes en
conditions totalement saturées sont examinées afin d’évaluer l’effet de la force de traînée. Pour l’étude géomécanique, une série
d’essais de compression à teneur en eau constante ont été réalisés pour évaluer le comportement mécanique d’éprouvettes
reconstituées de sable non saturé et non mouillant. Les relations contrainte-déformation en fonction du degré de saturation sous
condition de confinement sont étudiées afin de dériver les contraintes de succion. Les résultats soulignent que la modification de
surface à l'échelle nanométrique détermine la configuration spatiale de la phase aqueuse dans l'espace poreux et son impact sur
l'écoulement du fluide et sur la résistance avec la variation du degré de saturation.
KEYWORDS: non-wettable sands, water repellency, friction angle, critical pressure, hydraulic conductivity
MOTS-CLÉS : sables non mouillants, hydrophobie, angle de frottement, pression critique, conductivité hydraulique
1 INTRODUCTION
Soils in nature often become hydrophobic (non-wettable)
features, due to organic pollutants, natural hazards such as
wildfire and environmental pollution accidents such as oil spill,
whereas the accumulated geotechnical knowledge tends to be
somewhat limited to hydrophilic (wettable) soils, particularly in
the field of unsaturated soil mechanics.
Rodriguez et al. (1997) defined that the cause of the soil
particles property which draw water is the high surface free
energy. On the contrary, surface of hydrophobic soil particle
excludes water and acts as a diffusion barrier which disturb
substances diffuse by water (Goebel et al., 2007). Water layer
formed on the hydrophilic soil particle is 10 times thicker than
the water layer of the hydrophobic soil particle (Derjaguin and
Churaev, 1986). Such differences in surface properties of soils
result in clear distinctions even in macro scale (Frattolillo et al.,
2005; Nguyen et al., 1999). Therefore, the surface wettability at
particle scale controls the macro scale manifestation in soils.
Previous studies have been carried out so as to examine the
relationship between the suction and the shear strength using the
direct shear test for natural soils (e.g., Donald, 1956; Escario,
1980; Escario and Saez, 1986; Gan et al., 1988; Kim et al.,
2010a), exhibiting that the suction developed at inter-particle
contact causes the unique evolution of shear strength in natural
soils. The degree of saturation for both hydrophilic and
hydrophobic sands imposes the different evolution of thermal
and electrical conduction as well as the friction angle (Byun et
al., 2011; Kim et al., 2010b), attributed to the surface wettability.
This paper presents the series of experimentation to capture
the surface wettability effect with the scope of hydraulic and
geomechanical behaviors of both hydrophilic and hydrophobic
soils. Moreover, it is examined on how the existence of the
meniscus water affects the shear behavior using a direct shear
apparatus.
2 EXPERIMENTAL STUDY
2.1
Materials
The granular materials used in this study were Jumunjin sands
(specific gravity
G
s
=2.59, maximum porosity
n
max
= 0.465,
minimum porosity
n
min
= 0.375). This materials are reletively
uniformized (coefficient of uniformity
C
u
=1.16) with the mean
particle size
D
50
=0.5mm. Sands without any treatment were
tested for wettable (hydrophilic) samples whereas the non-
wettable samples were sands chemically treated by silylation
process (Zycosoil manufactured by Zydex industries, dilluted
ratio=1:100 with water). Cleaned sands were fully submerged
within the reactive solution and the reaction was allowed for 72
hours at room temperature condition. The recation formed
Park S.- .
