381
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Duncan-Chang - Parameters for Hyperbolic Stress Strain Behaviour of Soft
Bangkok Clay
Duncan-Chang - Paramètres de comportement contrainte-déformation hyperbolique d’argile molle
de Bangkok
Likitlersuang S.
Chulalongkorn University, Bangkok, Thailand
Surarak C., Balasubramania A., Oh E.
Griffith University Gold Coast Campus, Queensland, Australia
Syeung Ryull K.
Asian Institute of Technology, Bangkok, Thailand
Wanatowski D.
University of Nottingham, United Kingdom
ABSTRACT: This paper is on the analyses of the stress strain data of soft and stiff Bangkok Clays carried out at the Asian Institute of
Technology. A comprehensive series of triaxial tests both in compression and extension was carried out and the results were
compared with a number of stress-strain theories as based on critical state concepts. The finite element software PLAXIS contains the
Hardening Soil Model as an extension of the Duncan-Chang hyperbolic stress strain model. In this paper, the parameters for the
hyperbolic stress stain model are evaluated from the data gathered previously in testing soft and stiff Bangkok clays. The testing
program includes two series of undrained and drained tests performed on isotropically consolidated triaxial samples both under
compression and extension conditions. These testing results can be used to determine the undrained and drained shear strength
parameters for soft and stiff Bangkok Clays. Finally, two set of undrained and drained shear strength and stiffness parameters for the
Hardening Soil Model of soft and stiff Bangkok Clays are presented.
RÉSUMÉ: Cet article porte sur les analyses des données de contrainte-déformation des argiles molles et rigides Bangkok menées à
l’Institut asiatique de technologie. Une série complète d’essais triaxiaux portent à la fois sur la compression et l’extension a été
réalisée, et les résultats ont été comparés avec un certain nombre de contraintes-déformations, théories basées sur des concepts d’état
critique. Le logiciel PLAXIS contient le modèle Hardening Soil comme une extension du modèle de contrainte hyperbolique de
Duncan-Chang. Dans le présent document, les paramètres du modèle hyperbolique de contraintes sont évalués à partir des données
recueillies pour tester les argiles douces et raides Bangkok. Le programme comprend deux séries d’essais non drainés et drainés,
effectués sur des échantillons triaxiaux isotropes consolidés à la fois dans des conditions de compression et d’extension. Ces résultats
d’essai peuvent être utilisés pour déterminer les paramètres non drainés et drainés de résistance au cisaillement des argiles molles et
raides de Bangkok. Enfin, deux résultats de la résistance au cisaillement, non drainée et drainée, et des paramètres de rigidité pour le
modèle des argiles molles et rigides Bangkok sont présentés.
KEYWORDS: shear strength parameters, hardening soil model, triaxial tests, Bangkok clay, finite element analysis
1. INTRODUCTION
Bangkok subsoils are one of the most well-known sedimentary
soils and have been studied extensively in the past by many
research students at the Asian Institute of Technology under the
supervision of the fourth author. The experimental work was on
isotropically and anisotropically consolidated triaxial tests both
in compression and in extension. The results were primarily
used to verify the critical state theories as developed for
normally and overconsolidated clays (Balasubramaniam &
Chaudry, 1978; Balasubramaniam
et al.
, 1978, 1992;
Balasubramaniam & Hwang, 1980). Recently, soil models used
in PLAXIS such as the Hardening Soil Model (HSM), and the
Hardening Soil Model with Small Strain Behaviour (HSS) were
studied by Surarak (2010) on the applications in the design and
performance of deep excavations and tunnelling works in
Bangkok MRT project. The HSM have been developed under
the framework of the Duncan-Chang hyperbolic stress strain
theory. This paper presents the work on stiffness and strength
parameters based on Duncan-Chang theory.
2. GEOLOGICAL CONDITIONS OF BANGKOK SUBSOIL
The Bangkok subsoil forms a part of the larger Chao Phraya
Plain and consists of a broad basin filled with sedimentary soil
deposits. These deposits form alternate layers of sand, gravel
and clay. While the depth of the bedrock is still undetermined,
its level in the Bangkok area is known to vary between 400 m to
1,800 m depth. Based on extensive field and laboratory studies
carried out in the past by numerous researchers at AIT, the
following descriptions have been proposed for the Bangkok
clays: (1) Weathered Crust – the upper most layer (1 – 3 m), (2)
Very Soft to Soft Bangkok Clays (3 – 12 m), (3) Stiff to Very
Stiff Bangkok Clays (15 – 35 m). The index properties for
Weathered, Soft and Stiff Bangkok Clays are summarised in
Table 1.
Table 1. Index Properties of Bangkok Clays
Properties
Weathered
Clay
Soft Clay
Stiff Clay
Natural water content (%)
133 ± 5
122 – 130 20 – 24
Natural voids ratio
3.86 ± 0.15 3.11 - 3.64 1.10 - 1.30
Grain size distribution
Sand (%)
7.5
4.0
23
Silt (%)
23.5
31.7
43
Clay (%)
69
64.3
34
Specific gravity
2.73
2.75
2.74
Liquid limit (%)
123 ± 2
118 ± 1
46 ± 2
Plastic limit (%)
41 ± 2
43 ± 0.5
19 ± 2
Dry unit weight (kN/m
3
)
15.8 ± 0.3
16.5
15.5 -16.5
Consistency
Soft
Soft
Stiff
