Unit Cell Testing of Reinforced Soils - Reinforced Soil Engineering: Advances in Research and Practice - page 58

Figure 12b shows the results for unreinforced and reinforced clay
specimens. There was a relationship between values of Dc u and a for different
materials. The results were applied to the analysis of simulated earth walls.
Ingold and Miller (1982b) extended their study to reinforced clay under
undrained conditions and sheared by plane strain compression. Plastic geogrid
was used to reinforce London clay, and the test was performed in a plane strain
apparatus. It was considered that the reinforcement had imparted an equivalent
undrained shear strength to the clay. That is,

c u ¼ c u ð

1 þ aB = 4S Þ ð 39 Þ

where a is the adhesion factor. A comparison between this theory and
experimental results gave favorable agreement.
Yamauchi (1986) performed triaxial compression tests on unreinforced as
well as reinforced Kanto loam (silty clay) specimens. These tests were performed
at an effective confining stress of 50 kPa subjected to a back pressure of 200 kPa.
Four layers of nonwoven geotextile were used in the reinforced specimen. These
test results were reported in Murata et al. (1991) as well.
As shown in Fig. 13a , almost no effect of reinforcement was realized for the
undrained test. For the drained test (Fig. 13b), reinforcement effect in terms of
strength increase was realized, but the stiffness was much smaller in the
reinforced specimen when compared to the unreinforced one. The difference in
the ultimate strength between the drained and undrained tests can be explained by
two factors—the effect of tensile reinforcing and the effect of excess pore water
pressure due to the compressibility of the nonwoven geotextile. Because the
effect of the latter was not realized in the drained test, the overall effect was
positive. For the undrained tests, the effects due to these two factors may have
been balanced.
Fabian (1988) performed triaxial undrained and drained compression tests
on a Kaolin clay reinforced with different kinds of geosynthetic. In the undrained
tests, unconsolidated and consolidated tests were performed. A lower stiffness
was noticed for the reinforced specimen when compared to the unreinforced one,
especially the strength ratio was less than or about unity for some of the
unconsolidated undrained tests. In the drained tests, a similar finding to
Yamauchi's (1986) was obtained. The strength ratio was greater than unity, but
the stiffness was much lower in the reinforced specimens when compared to the
unreinforced specimens.
It was shown in his study that geosynthetics with drainage capability helps
in improving the undrained strength of reinforced clay. He provided a similar
reason to Ingold's (1982a) regarding the lower strength in reinforced specimen
when compared to the corresponding unreinforced specimen. That is, a higher
excess pore water pressure generated in the middle of specimen led to