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

FAKHER & JONES • When Bending Stiffness of Geosynthetic Reinforcement is Important
Vertical stress under footing (N/mm)
2.4
2.0
1.6
1.2
0.8
0.4
0.0
f-29, I = 2.15e-6 f-20, I = 7.64 e-7
f-26, I = 2e-7 f-27, I = 8.5e-8
f-28, I = 1e-8 f-20, no reinf.
f-20, cable
0 5 10 15 20 25
Vertical displacement (mm)
Figure 3. The influence of the reinforcement bending stiffness on the displacement of the
footing under different loads (values of I are in m 4 ).
neering judgement. A constant value for the modulus of elasticity, E, was chosen for
the reinforcement and the bending stiffness, EI, varied by varying the second moment
of area, I. The results show that the higher the bending stiffness the higher the potential
bearing capacity (Figure 3). This confirmed the conclusion derived from previous unitcell
shear box studies and scale-model loading tests (Fakher et al. 1996; Fakher and
Jones 1996b; Zakaria 1994).
3.1 Effect of Bending Stiffness of the Reinforcement
The effect of the reinforcement bending stiffness on the bearing load is shown in Figure
4 (when the vertical displacement/load width ratio, s/B = 0.3). It can be seen that
the presence of any type of reinforcement, with or without bending stiffness, has an
influence.
The deformed shape of a geosynthetic reinforcing material modelled as a cable or a
beam element with different stiffnesses, EI, is shown in Figure 5. An explanation for
the deformed shape of the reinforcement is that, as the footing moves vertically, the
adjacent super soft clay moves laterally. This results in ground surface heave adjacent
to the footing. The displacement of the super soft clay and the heave is influenced by
the in plane stiffness of the reinforcement. When the bending stiffness of the reinforcement
is high the heave is reduced and distributed over a wider area.
450 GEOSYNTHETICS INTERNATIONAL • 2001, VOL. 8, NO. 5