Unit Cell Testing of Reinforced Soils - Reinforced Soil Engineering: Advances in Research and Practice - page 41

2.1 Triaxial Compression Test

Broms (1977) tested a dry fine sand reinforced with geotextile in a triaxial
apparatus to study the effects of spacing, relative density of sand, and confining
pressure on the strength of reinforced soil. As can be seen in Fig. 4 , the inclusion
of geotextile at the specimen mid-height increased the strength. Moreover, the
effect of reinforcement, in terms of strength increase, is found to be dependent on
the confining stress.
He proposed an equation for calculating the ultimate load in a reinforced
soil (Fig. 5a) :

ps ho K av D 2
2tan 2 f a

exp 2tanf a R

2tanf a R

P ¼

DK av 2 DK av 2 1

ð 9 Þ

Where

P: ultimate axial load,
s 0 ho : lateral confining pressure at the perimeter of the specimen,
K av : coefficient of lateral earth pressure,
f 0 a : frictional angle between the soil and geotextile,
D: geotextile spacing,
R: radius of soil specimen.

In deriving Eq. (9), it is assumed that the stress condition in the soil
between the adjacent geotextile discs is constant at the radius r. This is, however,
only an approximation of the actual stress condition. An averaged value between
the Rankine coefficient for active earth pressure K a and K b ¼ 2tan 2 f 0 Þ

is
used for obtaining K av . Equation (9) has since been modified for prediction of
ultimate load in reinforced sand under axisymmetric loading through the use of a
multiplication factor (Chandrasekaran et al., 1989):

1 =ð 1 þ

ps ho K av RD
K a tan

af a Þ

exp tan

R
DK av 2

ð

P ¼ 1 ð 10 Þ

ð af a Þ

An equation has also been proposed for determining the tensile force in the
reinforcement:

s ho K av D
K a

af a Þ
DK av

R 2 r 2

R 2

exp tan

ð 2

T ¼ 1 ð 11 Þ

which gives the maximum tensile load in it as

s ho K av D
K a

af a Þ
DK av

exp tan

ð

T ¼ R 2 1 ð 12 Þ