Modeling the Time-Dependent Behavior of Geosynthetically Reinforced Soil Structures with Cohesive Backfill - Reinforced Soil Engineering: Advances in Research and Practice - page 72

7 CHARACTERIZATION OF GEOSYNTHETIC
REINFORCEMENT

Over the years, a large amount of experimental work has been done to study the
time-dependent behavior of geosynthetic reinforcement (Kaliakin and Decha-
sakulsom, 2001a). The majority of these studies focused on creep response, with
relaxation experiments perceived as overly complex. Numerous mathematical
models of the geosynthetics, possessing varying levels of sophistication, have
been developed in conjunction with many of the aforementioned experimental
studies. With minor exceptions, for purposes of mathematically representing
typical geosynthetic reinforcement, the models have assumed uniaxial stress and
strain states. This is in keeping with the observation (den Hoedt et al., 1994) that
geosynthetics commonly used for reinforcement exhibit negligible lateral

contraction.
Some models proposed to simulate creep and relaxation response of
geosynthetics are reviewed next. The discussion is limited to response under
isothermal conditions, as very few models have been proposed that account for
both thermal and mechanical response. A more thorough overview of time-
dependent models for geosynthetic reinforcement is available in Kaliakin and
Dechasakulsom (2001b).

7.1 Models Proposed to Simulate Creep Response

The most basic models developed to simulate creep response of geosynthetics are
simple, empirical, mathematical equations. For example, the following

expressions have been proposed:

¼

1 o þ

ð Þ

1 A log t 1

1 o 1 þ t n 1 ¼ þ ð 2 Þ

1 1 t n

1 ¼ ð 3 Þ

1 ð t Þ¼ m log 10 t þ 1 ð t o Þ ð 4 Þ

In Eq. (1), 1 represents the total strain, 1 o and A are functions of stress,
temperature, and nature of the material, and t denotes time. Using this expression,
Finnigan (1977) and Van Leeuween (1977) have reported success in modeling
short-term creep behavior.
In Eq. (2), which was developed by Findley (1987) for polyvinyl chloride
(PVC) and polyethylene (PE), 1 represents the strain, t is the time, and 1 o , 1 þ ,
and n are constants. From other work (Findley et al. 1976), it has been shown that