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

FAKHER & JONES • When Bending Stiffness of Geosynthetic Reinforcement is Important
Yd / B
0.18
0.12
0.06
0.00
-0.06
-0.12
-0.18
-0.24
-0.30
f-20, beam, s/B = 0.3
f-20, cable, s/B = 0.3
f-20, beam, s/B = 0.1
f-20, cable, s/B = 0.1
0 1 2 3 4 5 6
X / B
Figure 12.
settlement.
The deformed shape of the geosynthetic reinforcement with increasing
maximum heave increases from 1.8 B to 2.5 B for the case studied. If the bending stiffness
of the geosynthetic reinforcement is neglected, heave occurs close to the footing
and the horizontal location of the point of maximum heave is not influenced by an
increase in s/B.
3.6 Ground Surface Heave
Figure 13 shows the deformed shape of the ground surface. When beam elements are
used to model the geosynthetic reinforcement, a smaller heave occurs, and the location
of maximum heave occurs at a distance further from the footing than the case when
cable elements are used.
Contours of normalised vertical displacement, Y d /B, plotted over an area of
4B × 3.5B are shown in Figure 14. An interesting observation is that the maximum
heave (positive values of Y d ) does not occur at the ground surface when beam elements
are used (Figure 14c). The implication is that the reinforcement bending stiffness plays
a significant role in preventing heave of the super soft clay from being transferred to
the sand layer and ground surface.
3.7 Overall Discussion
When a footing overlying a layer of super soft clay settles, the clay beneath the footing
moves laterally to escape toward the ground surface resulting in heave. Control of the
resultant heave is a key factor to the successful construction over super soft clay and in
the bearing capacity mechanism. The reinforcement bending stiffness plays a significant
role in preventing the heave of the super soft clay being transferred to the sand
456 GEOSYNTHETICS INTERNATIONAL • 2001, VOL. 8, NO. 5