Geoscience Reference
In-Depth Information
Generally, the effect of the reinforcement can be seen when the tensile
strains of the geogrid increase with the deformation of the reinforced soil. To gain
insight into the relationship between the effect of the reinforcement and the
deformation of the soil, mean stress-strain relationships of the reinforced zone
were calculated from the acceleration records. The applied method for the stress-
strain calculation was proposed by Koga et al. (1990) and is briefly summarized
in Fig. 15. The used acceleration records were measured at A21, A22 and A23.
The records were filtered for cutting out frequencies of less than 0.4 Hz and
greater than 10 Hz; thus no residual strain was included in the results. The
calculated stress-strain relationships in step 3 shaking are shown in Fig. 16 for
the cases of D60-150, L60-150, D45-150, and L45-150. From the stress-
strain relationships, it can be seen that the secant shear modulus becomes larger
and the amplitude of strain becomes smaller as the length of geogrids and the dry
density of the soil increase.
The secant shear modulus in Fig. 16 was the slope of the approximated line
of stress-strain relations calculated by the least-squares method. The secant
shear modulus is plotted against the permanent horizontal displacement of the
wall face near the top of the wall at the height of 6.75 m in Fig. 17 . In all cases, the
secant shear modulus decreased with the permanent lateral displacement of
the soil wall. However, the secant shear modulus increased when the permanent
displacement of the soil reached a certain level. These turning points in the
variation of the shear modulus with the displacement of the reinforced soil should
be the points where the strained reinforcement showed its effectiveness in
preventing the further deformation of the wall discussed in Figs. 10 and 11 . These
points varied according to the compaction level of the soil. There are differences
in the horizontal displacement of the facing top at the turning point between
two soils with different densities. These were about 1% of the wall height for
Figure 15 Calculation of shear stress and strain from acceleration records. (Modified
from Takahashi et al., 2001.)
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