Technical Paper by A. Fakher and C.J.F.P. Jones WHEN THE ...

FAKHER & JONES • When Bending Stiffness of Geosynthetic Reinforcement is Important
0.15
0.10
0.05
Figure 13.
Yd / B
0.00
-0.05
-0.10
f-20, no-reinf., s/B = 0.3
-0.15
f-20, beam, s/B = 0.3
-0.20
-0.25
f-20, cable, s/B = 0.2
-0.30
0 2 4 6 8 10
X / B
The deformed shape of the ground surface.
layer. When the bending stiffness of the reinforcement is high, the heave is reduced
and distributed over a wider area. It can be concluded that the use of geosynthetic reinforcement
having a stiff three-dimensional structure, such as a geocell, is beneficial.
The structural behaviour of the geosynthetic in this situation can be likened to a
plate that has bending stiffness (flexural rigidity) and tensile stiffness. The plate-type
behaviour of reinforcement, with bending stiffness, overlaying super soft clay provides
more than a large displacement mechanism, such as a membrane-type support
system (Burd 1995). The plate-type behaviour starts with a small vertical deflection of
the reinforcement and distributes the heave of the ground surface over a wider area as
the vertical deflection of the footing increases. It is seen that as the size of the footing
increases, the influence of the bending stiffness of the reinforcement decreases
sharply; this confirms the plate-type behaviour of the mechanism.
When a fill is being spread on the geosynthetic overlying the super soft clay, the
surface layer of the clay tends to move laterally, pushed out by the spreading layers of
soil. Consequently, a tensile force is developed in the geosynthetic reinforcement due
to lateral movement of the soil. This tensile force needs to be sustained by the anchorage
of the reinforcement; this is provided by the pull out resistance of the reinforcement
at the interface of the sand and clay. As the reinforcement tensile stiffness
increases, the required pull out displacement to mobilise the maximum pull out resistance
decreases. Hence, a geosynthetic reinforcement with a high tensile stiffness (as
opposed to high bending stiffness) provides a better anchorage in the soils resulting in
an increase in the bearing capacity.
4 CONCLUSIONS
The bending stiffness of geosynthetic reinforcement is neglected in most design prac-
GEOSYNTHETICS INTERNATIONAL • 2001, VOL. 8, NO. 5 457