Geosynthetic Reinforced Containment Dike Constructed over Soft Foundation: Numerical Analysis - Reinforced Soil Engineering: Advances in Research and Practice - page 280

A high-strength woven geotextile, manufactured from polyester, was
installed under the embankment/foundation to tensile-reinforce the foundation
and also acted as separator. The wick drains extended approximately 40 0 (13.3m)
into the foundation to accelerate consolidation of the top portion of foundation
soil, that is, Strata 1 and 2A. The wick drains were 4 00 (10 cm) wide and 0.25 00
(0.64 cm) thick. They contained plastic cores to allow free vertical flow of pore
water and were covered by a geotextile.
The instrumentation scheme included 42 settlement plates, 3 inclinometers,
and 25 piezometers along the critical riverward portion of the dike. The measured
settlement ranged from 1.5 00 to 10 00 (13.8 to 25.4 cm) along the centerline and
between 4 00 and 4.5 00 (10.2 to 11.25 cm) along the dike exterior slope 5 years after
construction. Most lateral movements were detected during construction. The
piezometric reading leveled off following completion of construction.
A total of 66 strain gauges were installed in the geotextile along the three
terminals (each having 22 strain gauges). The total strains in the geotextile ranged
from 1.8 to 3.0% in the fill direction and 1.9 to 3.1% in the wrap direction. The
geotextile continued to creep after construction. About half of the instruments
were still functioning 3.5 years after construction.

4 FINITE-ELEMENT ANALYSIS

The anisotropic bounding surface elastoplastic model (Yue, 2001; Ling et al.,
2002) was incorporated into a general-purpose finite-element program SAC-2
(Herrmann and Kaliakin, 1987) for the analysis. This version of model requires
12 input parameters. A material subroutine describing the proposed model was
coded to provide SAC-2 with the material matrix to deal with the anisotropic
clays. The numerical scheme of implementation is in principle similar to that
outlined by Herrmann et al. (1987).
The containment dike and foundation soil were idealized as plane strain
based on the assumptions that the curvature of the embankment could be
neglected and the three-dimensional configuration of the wick drains could be
idealized as two dimensions through a separate procedure as described
subsequently. Figure 3 shows the mesh for finite-element analysis. It consisted of
175, 21, and 46 elements for the foundation, fill and geotextile, respectively.
The construction stages were simulated using the incremental construction
option of the program. A total of 1800 days and 132 increments, with a time step
of 10-15 days per increment, was included in the analysis. Considering the
extremely poor drainage conditions of the soft clays, Stage I was treated as
instantaneous loading through the fill elements at the beginning of calculation,
and the wick drains were assumed to take effect at the very beginning (time
t

¼ 0). Consolidation was allowed for a year until Stage II was initiated.