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Study on New Method of Accelerated Clay Creep Characteristics Test
Étude d’une nouvelle méthode d’évaluation accélérée des caractéristiques de fluage des argiles
Ye Y., Zhang Q., Cai D., Chen F., Yao J., Wang L.
Railway Engineering Research Institute, China Academy of Rails Science, Beijing,100081
State Key Lab for Track Technology of High-speed Railway, China Academy of Rails Science, Beijing,100081
ABSTRACT: Long-term creep tests, dynamic triaxial tests and corresponding scanning electron microscope(SEM) test were carried
out for remolded saturated clay to study the way of rapid acquisition of the creep characteristics. The creep deformation and
permanent deformation under the cyclic loading of soil with same initial state were analyzed. Based on the principle of static stress
and dynamic stress equivalent, and the creep time and the cyclic number equivalent, a method using the relationship between stress-
strain-cyclic number to predict the creep deformation was established. The SEM test results showed that the clay microstructure
changing trend of creep test and dynamic triaxial test were similar. The multilevel stress and long-term creep deformation can be
predicted by the proposed method.
RÉSUMÉ :Des essais de fluage à long terme, des essais triaxiaux dynamiques ainsi que des observations correspondantes faites au
microscope électronique à balayage (MEB) ont été réalisés sur une argile saturée remaniée pour étudier la possibilité d’acquérir
rapidement les caractéristiques de fluage du matériau. On a analysé comparativement les déformations de fluage et les déformations
permanentes obtenues sous chargement cyclique à partir du même état initial. En se basant sur le principe d’équivalence entre
contrainte statique et contrainte dynamique, ainsi que sur l’équivalence entre le temps de fluage et le nombre de cycles, une méthode
de prévision des déformations de fluage a été établie, basée sur la relation entre contrainte, déformation et nombre de cycles. Les
images obtenues au MEB ont montré que les évolutions de microstructures obtenues dans les essais de fluage et dans les essais
triaxiaux dynamiques étaient similaires. Les déformations de fluage à long terme peuvent donc être évaluées à partir de la méthode
proposée.
KEYWORDS: Remolded Saturated Clay; Creep; Acceleration; Equivalent efficiency; Dynamic triaxial test
MOTS-CLÉS : argile saturée remaniée, fluage, accélération, efficacité équivalente, essai triaxial dynamique.
1 INTRODUCTION.
Because of the great deep and long draining path, there are the
characteristics of chronicity and complexity in composite
foundation substratum deformation. So the deformation of
substratum is the main resource of foundation deformation. The
creep has been the key problem of the infrastructure with high
standard including high-speed railway
（
Liu Junfei ZhaoJian
ZhaoGuotang et al. 2011, Cai Degou Ye Yangsheng Yan
Hongye et al. 2010
）
. For the purpose of ensuring foundation
stability and meeting the requirement of engineering design, it
is very vital to research the method which can obtain creep
characteristic of foundation soil quickly.
According to related reference, there are two reasons for
creep. One is that deviator stress leads to viscous shear flow; the
other is that spherical stress leads to viscous body flow (Li Xiao
2011). Clay grains are connected by hydrated film, so it has
inherent cohesion and rheological behavior. Only the hydrated
film is extruded under low stress level, so the deformation is
elastic. When the stress level is raised, stress concentrations will
happen among grains. Soil grains will contact directly
dislocation and rearrange. So the permanent deformation
generates (He Kaisheng and ShenZhujiang 2003). The
deformation of soil under load is the synthetic result of
microstructure change, such as structure bond failure,
dislocation and porosity change (Zhang Xianwei Wang
Changming and Li Junxia 2010).
The evident characteristics of soil stress-strain are nonlinear,
hysteretic and cumulative under dynamic load. When dynamic
stress level is low, elastic deformation is dominating. With the
increasing of dynamic stress level, the permanent deformation
increases gradually. Under different cyclic number and dynamic
stress level, the soil grain adjusts and rearranges to some degree.
In nature, there is correlation between microstructure change
and macrostructure deformation (Liu Sha 2008). It is concluded
that the deformation in macrostructure is a pattern of
appearance of microstructure change.
2 CREEP AND DYNAMIC TRIAXIAL TEST AND
RESULTS ANALYSIS
2.1
Parameters of Soil
Remolded saturated clay is used to experiment. Its parameters
can be seen in Table 1 and Figure 1.
Table 1. Parameters of Soil
Specific
gravity
Liquid limit
（
%
）
Plastic limit
（
%
）
Plasticity
index
2.70
45.5
23.0
22.5
The samples used to creep and cyclic triaxial test were
prepared as follows: Clay with moisture content over liquid
limit was consolidated under certain load until 50kPa. That can
ensure soil with the same stress history and the same
consistency. The samples (Φ39.1 (mm) × H80 (mm) used to
creep test and Φ50 (mm) × H100 (mm) used to dynamic triaxial
test) were consolidated isotropically in chamber under 50kPa.
The chamber pressure during test is 50kPa. Creep soil samples
were sheared by respective loading in triaxial creep apparatus
under drained and undrained condition. Dynamic triaxial test
samples were sheared under undrained and 5Hz condition.
