Geotextile containers - Geosystems: Design Rules and Applications - page 91

G = submerged weight of the layer of geotextile containers per unit length [N/m];

stack

= height of the stack [m].

The value of the surface friction coefficient between the adjacent geotextile con-
tainers depends on the type of geotextile used and can be tested when considered
critical. For woven polypropylene geotextiles used in the geotextile container it may
be approximated to:

otan 35 ° < tan30t °

(6.21)

6.5.8 Influence of wave-induced liquefaction
Loosely placed sand has a tendency to compact under cyclic loading. When the pores
are saturated with water, as is the case with geotextile containers under water, any
water is expelled from the pores during compression. The pore-water flow necessary
for this to occur requires a differential between the pore-water pressure inside and
outside the geotextile container. When a cyclic load is applied to geotextile contain-
ers with loosely packed, saturated sand, excess pore pressures are created. In certain
conditions these excess pore pressures can equal the weight of the upper-lying sand,
causing liquefaction.
After a certain time the pore-water has dissipated, the sand will partially compact,
giving rise to reduced susceptibility to further compaction and excess hydrostatic pres-
sures. In time, the sand becomes so tightly packed that no excess hydrostatic pressure
is generated any longer.
In section 6.3 of [16] a method is described to determine the liquefaction susceptibil-
ity of the sand in a geotextile container lying on the sea bed when it is subject to waves.
According to this method there is no liquefaction problem if the wave period T is 3 s to
12 s, if the wave height gradually increases during a period of several hours and if:

2

2

d d ρ gd

2

α ⋅ g ⋅

T 300

(6.22)

w w

gd

c

<< == s

k

c

v s

Δ n n ⋅

T 3000 s

(6.23)

n

<<

=

( )

( )

αψ
c

n

⋅ ⋅

−

0 0

c

where:

d

= characteristic drainage period [s];

n

= characteristic compression period [s];

d = drainage distance ≈ height of the container [m];

v

= consolidation coefficient for the grain skeleton [m 2 /s];

s

= permeability of the fill material (sand) [m/s];

n = porosity of the fill material (sand) [-];

n

= porosity reduction under constant wave load [-];

α c = one-dimensional compressibility of the grain skeleton upon discharge [m 2 /kN];

ψ 0 = generation of excess pore pressure for undrained load [N/m 2 s].