1171
Application of micro-porous membrane technology for measurement of soil-water
characteristic curve
Application de la technologie de membrane microporeuse pour la détermination de la courbe de
rétention d’eau des sols
Nishimura T.
Department of Civil Engineering, Ashikaga Institute of Technology, Japan
ABSTRACT: This study focuses on the use of micro-porous membranes instead of ceramic disks for improving the time required to
reach matric suction equalization. Measurements of the soil-water characteristic curve were conducted using micro-porous
membranes in a new pressure plate apparatus. In the testing program, the hydraulic response of the micro-porous membrane under
varying water contents corresponding to increasing or decreasing matric suction was measured. Different micro-porous membrane
with different air entry values were investigated in order to compare the time required for matric suction equilibrium with that of the
ceramic disk. Soil-water characteristic curves of different types of soil were measured using the axis-translation technique with both
the micro-porous membrane and the ceramic disk.
RÉSUMÉ : Cette étude concerne l’utilisation des membranes microporeuses à la place des disques céramiques pour réduire le temps
nécessaire pour atteindre l’équilibre en succion matricielle dans les sols. La détermination de la courbe de rétention d’eau a été faite
en utilisant des membranes microporeuses dans un nouvel appareil de plaque de pression. Dans le programme d’essais, la réponse
hydraulique de la membrane microporeuse sous des teneurs en eau variables correspondant à des augmentations ou diminutions de
succion matricielle a été mesurée. Des membranes microporeuses différentes avec des points d’entrée d’air différents ont été étudiées
afin de comparer le temps nécessaire pour atteindre l’équilibre en succion matricielle avec le temps dans le cas du disque céramique.
Les courbes de rétention d’eau de différents sols ont été déterminées en appliquant la technique de la translation d’axe avec la
membrane microporeuse et le disque céramique.
KEYWORDS: unsaturated soils, soil-water characteristic curve, matric suction, pressure membrane technique
1 INTRODUCTION
Unsaturated soil mechanics is becoming more widely accepted
in geotechnical engineering and engineering protocols are
emerging for a range of geotechnical problems. Matric suction
plays an extremely important role in describing unsaturated soil
property functions as well as the verification of the unsaturated
soils mechanics theories (Gasmo et al. 1999). The axis-
translation technique developed by Richards (1941) and the
pressure plate technique suggested by Hilf (1956) have
contributed significantly towards the measurement and control
of matric suction in unsaturated soils laboratory tests. Bishop
and Donald (1961) and Bishop and Henkel (1962) developed
the triaxial apparatus for unsaturated soils, and used the pressure
plate technique in order to separate the pore-air pressure and the
pore-water pressure. The pressure plate technique make use of
high air entry disks which allow the movement of water but
resist the movement of free air. High air entry ceramic disks are
generally made of sintered kaolin and have a thickness of 5 mm
or 7 mm when used as part of a pressure plate apparatus. The
ceramic disk is of extremely low permeability with respect to
water flow (i.e., about 1 x 10
-11
m/s; Fredlund and Rahardjo,
1993). Typical high air entry ceramic disk used in unsaturated
soil testing equipment, such as the triaxial, direct shear and
SWCC apparatuses are rated for air entry value of 1 bar, 3 bar, 5
bar and 15 bar (Padilla et al. 2006). The axis-translation
technique is performed by installing (i.e., sealing) a high air
entry disk into the base pedestal of a soil testing apparatus. One
of the concerns related to the use of high air entry ceramic disks
is the time required for equilibrium to be established in a soil
specimen. Tinjum et al. (1997) observed that the equilibrium in
the pressure plate was established between 5 and 8 days for
clayey soils. Consequently, the testing of unsaturated soils was
time consuming and therefore, costly. The long time required to
reach the equilibrium is particularly of concern for the
measurement the soil-water characteristic curves. This study
focuses on the use of micro-porous membranes instead of
ceramic disks for improving the time required to reach matric
suction equalization. Measurements of the soil-water
characteristic curve were conducted using micro-porous
membranes in a new pressure plate apparatus. In the testing
program, the hydraulic response of the micro-porous membrane
under varying water contents corresponding to increasing or
decreasing matric suction was measured. Different micro-
porous membrane with different air entry values were
investigated in order to compare the time required for matric
suction equilibrium with that of the ceramic disk. Soil-water
characteristic curves of different types of soil were measured
using the axis-translation technique with both the micro-porous
membrane and the ceramic disk.
2 TEST PROCEDURE
2.1 Soil material & micro-porous membrane
Five soil types were used in the study. The grain size
distribution curves of the soils are shown in Fig. 1. The micro-
porous membranes used in this study are a product
