TM 5-818-8/AFJMAN 32-1030
CHAPTER 4
G E O T E X T I L E REINFORCED EMBANKMENT ON SOFT FOUNDATION
and the dike, the geotextile will increase the
4-1. General
resisting forces of the foundation. Geotextile-
Quite often, conventional construction techniques
reinforced dikes may fail by fill material sliding
will not allow dikes or levees to be constructed on
off the geotextile surface, geotextile tensile failure,
very soft foundations because it may not be cost
or excessive geotextile elongation. These failures
effective, operationally practical, or technically
can be prevented by specifying the geotextiles that
feasible. Nevertheless, geotextile-reinforced dikes
meet the required tensile strength, tensile modu-
have been designed and constructed by being made
lus, and soil-geotextile friction properties.
to float on very soft foundations. Geotextiles used
e. Rotational Slope and/or Foundation Failure.
in those dikes alleviated many soft-ground founda-
Geotextile-reinforced dikes constructed to a given
tion dike construction problems because they per-
height and side slope will resist classic rotational
mit better equipment mobility, allow expedient
failure if the foundation and dike shear strengths
construction, and allow construction to design ele-
plus the geotextile tensile strength are adequate
vation without failure. This chapter will address
(fig 4-l b). The rotational failure mode of the dike
the potential failure modes and requirements for
can only occur through the foundation layer and
design and selection of geotextiles for reinforced
geotextile. For cohesionless fill materials, the dike
embankments.
side slopes are less than the internal angle of
4-2. Potential Embankment Failure Modes
friction. Since the geotextile does not have flexural
strength, it must be placed such that the critical
The design and construction of geotextile-rein-
arc determined from a conventional slope stability
forced dikes on soft foundations are technically
analysis intercepts the horizontal layer. Dikes
feasible, operationally practical, and cost effective
constructed on very soft foundations will require a
when compared with conventional soft foundation
high tensile strength geotextile to control the
construction methods and techniques. To success-
large unbalanced rotational moments.
fully design a dike on a very soft foundation, three
f. Excessive Vertical Foundation Displacements.
potential failure modes must be investigated (fig
Consolidation settlements of dike foundations,
4-1).
whether geotextile-reinforced or not, will be simi-
a. Horizontal sliding, and spreading of the em-
lar. Consolidation of geotextile-reinforced dikes
bankment and foundation.
usually results in more uniform settlements than
b. Rotational slope and/or foundation failure.
for non-reinforced dikes. Classic consolidation
c. Excessive vertical foundation displacement.
analysis is a well-known theory, and foundation
The geotextile must resist the unbalanced forces
consolidation analysis for geotextile-reinforced
necessary for dike stability and must develop
dikes seems to agree with predicted classical con-
moderate-to-high tensile forces at relatively low-to-
solidation values. Soft foundations may fail par-
moderate strains. It must exhibit enough soil-
tially or totally in bearing capacity before classic
fabric resistance to prevent pullout. The geotextile
foundation consolidation can occur. One purpose of
tensile forces resist the unbalanced forces, and its
geotextile reinforcement is to hold the dike to-
tensile modulus controls the vertical and horizon-
tal displacement of dike and foundation. Adequate
gether until foundation consolidation and strength
development of soil-geotextile friction allows the
increase can occur. Generally, only two types of
transfer of dike load to the geotextile. Developing
foundation bearing capacity failures may occur-
geotextile tensile stresses during construction at
partial or center-section foundation failure and
small material elongations or strains is essential.
rotational slope stability/foundation stability. Par-
d. Horizontal Sliding and Spreading. These
tial bearing failure, or "center sag" along the dike
types of failure of the dike and/or foundation may
alignment (fig 4-1 c), may be caused by improper
result from excessive lateral earth pressure (fig
construction procedure, like working in the center
4-1a). These forces are determined from the dike
of the dike before the geotextile edges are covered
height, slopes, and fill material properties. During
with fill materials to provide anchorage. If this
conventional construction the dikes would resist
procedure is used, geotextile tensile forces are not
these modes of failure through shear forces devel-
developed and no benefit is gained from the geo-
oped along the dike-foundation interface. Where
textile used. A foundation bearing capacity failure
geotextiles are used between the soft foundation
may occur as in conventional dike construction.
4-1
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