Unit Cell Testing of Reinforced Soils - Reinforced Soil Engineering: Advances in Research and Practice - page 39

where F is the tensile force developed in the reinforcement, and A is the cross-
sectional area of the specimen. If the spacing h is assumed to be small relative to
the specimen height, the following relationship is obtained by equating the
horizontal force:

A tan a
h

F ¼ T ð 5 Þ

where T is the force in a layer of reinforcement.
The major principal stress is s 1 ¼ð s 3 þ f 0 Þ:

T = h Þ tan acot ð a 2 Because

the maximum value of s 1 occurs at a ¼ 45 8 þ f 0 = 2 ;

it is found that

s 1 ¼ K p s 3 þ

K p T = h ð 6 Þ

This gives the increment in major principal stress as Ds 1 ¼ K p T = h ; which is

related to the cohesion as

K p T
2h

c 0 ¼ ð 7 Þ

The experimental results showed reasonable agreement with the theory,
which states that the effect of reinforcement is proportional to the tensile rupture
strength of reinforcement and inversely proportional to the spacing.

1.2 Confining Pressure Enhancing Concept

Yang (1972) conducted a series of triaxial tests on a cylindrical sand specimen
reinforced with discs of fiberglass net or stainless steel. He considered that sandy
soil, which is in fact cohesionless, should not be assumed to possess cohesion by
inclusion of reinforcement. According to him, the increase in strength due to
reinforcement should be regarded as a change in the stress state of soil that
resulted in an enhancement of confining stress, Ds 3 :
The reinforced sand failed at a constant effective stress ratio s 3 ¼

K a s 1 ;

in
which K a is obtained from the test of unreinforced specimen. Therefore,
the strength in a reinforced specimen is

s 1 ¼ K p s 3 þ Ds 3 ð 8 Þ

Hence, the increase in confining stress can be obtained as the measured value of
s 1 and s 3 for the reinforced specimen and f 0 for the corresponding unreinforced
specimen. Yang found that Ds 3 increased linearly with s 3 until a critical value is
reached, after which it remained constant (Fig. 3) . The test results indicated that
below this critical confining pressure, the strength of reinforced specimens was
controlled by either (1) the slippage at the interface between the reinforcement