Geoscience Reference
In-Depth Information
Figure 6.8
Field measurements Kandia dam: Filling of the second instrumented geotextile. The
unsaturated filling resulted in limited load being exerted on the geotextile during the fall.
Fall velocity and fall energy
The fall energy
E
fall
that has to be dissipated is kinetic energy. This can be written as:
1
(6.8)
2
E
A v
A
⋅
fall
2
ρ
where:
fall
=
fall energy per unit of length [J/m];
v
=
fall velocity of the geotextile container just before impact [m/s];
A
=
filled cross-sectional area of the geotextile container [m
2
];
ρ
=
density of the geotextile container [kg/m
3
].
The key parameter in determining the load upon impact on the bottom is the fall
velocity of the geotextile container. In Appendix G the development of the fall velocity
of the geotextile container during free fall is computed. The maximum fall velocity,
the so-called terminal velocity (
v
), is [22, paragraph 6.3]:
∞
V
AC
2
ρρ
−
⋅
(6.9)
w
v
g
∞
=
⋅
⋅
ρ
s
C
d
w
where:
v
∞
=
terminal velocity [m/s];
V
=
volume of the geotextile-encapsulated sand element [m
3
];
s
=
cross-sectional area in the horizontal plane [m
2
];
d
=
drag force-coefficient (approximately 1) [-].
The terminal velocity is theoretically only reached at a certain depth. In Figure 6.9
the fall velocity is calculated, using the formulae in Appendix G, as a function of
