Geoscience Reference
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Figure 6 Continued.
6 STRAIN IN GEOGRID
Figure 7a shows the strain measured in the upper surface (marked as IN) of
geogrid and its relation with the uplifting of the pipe. The compressive strain is
shown for the portion of geogrid that was bent and located close to the pipe. The
strain developed at strain gauge No. 22 and distributed toward the length of
geogrid. The tensile strain was measured for the lower surface of geogrid (marked
as OUT). Again, the tensile strain propagated from strain gauge No. 22 outwards.
The peak strain increased with the distance of uplifting.
The strain gauge readings indicated that the geogrid was not under pure
tension, but also subjected to bending moment. The bending moment in the
geogrid was the greatest around the vicinity of the pipe. Figure 7b shows the
strain measured at the lower surface of geogrid in test 2. Similar to the upper
surface, the tensile strain in the geogrid increased with the distance of uplifting,
and distributed toward the end of geogrid. The layer in between the grids was
subject to the same behavior.
Figure 8 shows the results for test 3, where gravel was used. The
compressive strains were recorded in the lower surface of geogrid, whereas its
upper surface was under tension. Thus by confining the backfill in between the
grid layer using gravels, an opposite pattern of strain development was noticed.
Figures 9 and 10 show the results when the soil cement was used. The
geogrid at the lower portion was not subject to any strains. The portion of the grid
near the pipe was under tension.
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