243
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Evaluation of Consolidation Behavior of Soils under Radial Drainage Condition
Using Digital Image Analysis
Évaluation du comportement de consolidation des sols sous des conditions de drainage radial
à partir de l'analyse d'image numérique
Kim J.-Y., Chung C.-K.
Department of Civil and Environmental Engineering, Seoul National University
Cho N.-G.
Hyundai Engneering & Construction
Yune C.-Y.
Department of Civil Engineering, Gangneung-Wonju National University
ABSTRACT: Most of the analytical solutions for consolidation under radial drainage are based on the assumption that only vertical
compression occurs. During consolidation, however, soils deform not only vertically but also radially. The radial deformation during
consolidation may induce additional excess pore pressure in a soil mass and unexpectedly cause differential settlement and produce
stresses in structures founded on consolidating ground. A new consolidation apparatus, which enables the deformation of a specimen
to be visually observed, and the total vertical stress as well as the pore water pressure to be measured, was developed. Consolidation
tests for reconstituted kaolinite specimens were performed using the new consolidation apparatus under radial drainage, along with
test under vertical drainage. Digital image analysis was adopted to analyze the consolidation deformation of the specimen. Radial
deformations as well as vertical deformations during consolidation were monitored and compared for the two different drainage
condition. Non-uniformities of the specimen induced during horizontal drainage were confirmed by measured total vertical stress.
RÉSUMÉ : La plupart des solutions analytiques pour la consolidation avec écoulement radial sont fondées sur l’hypothèse qu’il n’y a
que des compressions verticales. Cependant, pendant la consolidation, les sols se déforment non seulement verticalement mais aussi
radialement. La déformation radiale pendant la consolidation peut induire des surpressions interstitielles additionnelles dans le sol,
pouvant entraîner des tassements différentiels imprévus ainsi que des contraintes au sein des structures fondées sur le sol en cours de
consolidation. Un nouvel appareil de consolidation, qui permet d’observer visuellement la déformation d’une éprouvette et de mesurer
la contrainte verticale totale appliquée ainsi que la pression interstitielle, a été développé. Des essais de consolidation ont été réalisés
sur des éprouvettes de kaolinite reconstituées en utilisant le nouvel appareil de consolidation avec drainage radial, ainsi que des essais
avec drainage vertical. La technique d’analyse d’image numérique a été adoptée pour analyser les déformations de consolidation de
l’éprouvette. Les déformations radiales ainsi que les déformations verticales ont été mesurées et comparées pour les deux conditions
de drainage. Les hétérogénéités de l’éprouvette induites par le drainage horizontal ont été confirmées par la mesure de la contrainte
verticale totale.
KEYWORDS: consolidation, vertical drain, horizontal deformation, digital image analysis
MOTS-CLÉS : consolidation, drainage vertical, déformation horizontale, analyse d’image numérique
1 INTRODUCTION
Soft clayey soil ground under preloading improvement with
vertical drains has known to experience mostly vertical
deformation with radial drainage. However, even though no
radial displacement is expected in the present consolidation
theory, progressive consolidation process from vertical drains
induces void ratio variation in the radial direction, which is a
strong evidence of radial inward displacements of soils toward
drains (Yune 2005). These radial displacements during
consolidation have already been recognized by many
researchers. Pyrah and Tanaka (1999) and Atkinson et al.
(1985) investigated possibility of horizontal movements of soils
under radial drainage by measuring horizontal variations of
water contents of soil specimens at the end of consolidation.
Baek and Moriwaki (2004) measured directly the radial
displacements during consolidation by monitoring the
movements of magnets installed in the soil specimens.
Spatial variations of void ratio and excess pore pressure
yield the stiffness variation of soil ground and result in vertical
total stress change and excess pore pressure change under
constant vertical preloading. Accordingly, monotonic
dissipation of excess pore pressure is no longer possible, and
consolidation coupled with total stress change and radial
displacement will be the precise condition for soft ground under
preloading with vertical drains.
To obtain the precise and detailed information on the soil
behavior under vertical loading with radial drainage, physical
model test equipment under plane strain condition to monitor
the soil responses of entire zone under consideration throughout
the whole consolidation process was developed. Soil
movements during consolidation were determined by digital
image analysis using photo images. Detailed strains and void
ratios of entire soil specimen can be obtained. Also, variations
of total stress and pore pressure were also measured in several
locations in the specimen. Using reconstituted kaolinite
specimen, a test with horizontal drainage under vertical loading
was carried out, together with a test with vertical drainage.
Results from both tests are comparatively analyzed.
2. EXPERIMENTAL PROGRAM
2.1. Test apparatus
The schematic diagram of the consolidation testing apparatus
developed for this study is illustrated in Figure 1. The apparatus
takes a rectangular parallelepiped specimen of 150 mm in
height, 140 mm in width, and 40 mm in thickness, surrounded
by four transparent acrylic walls which enable monitoring the
internal movement of soils during consolidation. The photo
images on the front wall are used for digital image analysis to
find out the soil deformations during the entire consolidation
process. On the opposite side, 6 pore pressure transducers at 2
