Unit Cell Testing of Reinforced Soils - Reinforced Soil Engineering: Advances in Research and Practice - page 53

shearing, no positive effect of reinforcing was shown, but a difference was
noticed for the peak strength between the unreinforced and reinforced specimens.
Moreover, extensible and inextensible reinforcements lead to different
performance of the reinforced soil.
A consideration similar to that of Gray and Ohashi (1983) regarding the
increase in shear strength was put forward. They considered an overall effect of
reinforcement in increasing the shearing resistance of soil as expressed by the
mobilized angle of friction by an amount

P R
A s ð

cos utan f 0 þ

t EXT ¼ sin u Þ ð 29 Þ

By considering strain compatibility between extension in the surrounding
soil, mainly governed by plastic strain, and the reinforcement extension, the
following relationship was established to relate the increase in the maximum
reinforcement force, dP RM , with the shear displacement in sand, dx:
dP RM
dx ¼

K
L R cos u

sin ð c þ 2u Þ

tan c þ ð 30 Þ

cos c

where

cis the angle of dilation,
K is the stiffness of reinforcement,
L R is the length of reinforcement.
Other notations are indicated in Fig. 9a. A good agreement between
theoretical and experimental results was obtained. The angle of friction between
the reinforcement and soil was also estimated based on the experimental results,
and it was found that the direct shear angle of friction of soil can be the limiting
value for the bond.
In view of the importance of the thickness of the shear zone for predicting
the strength increase by reinforcement in a direct shear test, as proposed by Gray
and Ohashi (1983), Shewbridge and Sitar (1989) conducted a study to examine
the mechanism of shear zone development in it. Monterey sand #O was used with
different types of reinforcement. Based on observation, the geometry of
deformed reinforcement was proposed to be as shown in Fig. 10a, and the width
of the shear zone was found to be dependent on the reinforcement concentration,
stiffness, and bond between sand and reinforcement. It is wider in the reinforced
soil than in the unreinforced soil. Similar findings to those of Gray and Ohashi
(1983) were obtained regarding reinforcement stiffness, and reinforcement
concentration on the strength. Figure 10b shows the relationship between the
increase in strength and reinforcement ratio for all the tests. Whereas the
relationship was found to be linear by Gray and Ohashi (1983), it is was found to
be nonlinear by Shewbridge and Sitar (1989). In Shewbridge and Sitar (1990),