# 4.5 REINFORCED EARTH (terre armee)

```4.5 REINFORCED EARTH (terre
armee)
FILLS CAN BE FORMED PLACING &quot;REINFORCEMENTS&quot; IN
THEM AND COMPACTING (GLASS FIBRE REINFORCED,
PLASTIC FIBRE, TRYLENE FIBRE, FLEXIBLE GALVANISED
STEEL STRIPS ETC.) ( 5 MM THICK &amp; FLEXIBLE). THE STRIPS
ARE LAID IN THE LAYERS OF THE FILL AND BOLTED TO THE
RETAINING WALL AT THE FACING OF THE FILL. THESE
STRIPS EXTEND SUFFICIENTLY FAR INTO THE SOIL BEHIND
THE WALL. THE MAIN IDEA IS THAT WHEN SLIDING STARTS
TO OCCUR IN THE SOIL (ZONE 1) THE ANCHORED STRIPS
WILL PROVIDE A COMPLEMENTARY SHEAR STRENGTH
(ZONE 2) AND THERE WILL STOP FURTHER DEFORMATION.
FILL MATERIAL - SEVERAL SPEC'S
• GENERALLY SHOULD BE GRANULAR IN NATURE
PARTICLES D &lt; 80 mM SHOULD BE &lt; 15%
• MAX. PARTICLE SIZE: 350 MM
MAX. 25 % OF THE FILL &gt; 150 MM
• ANOTHER SPEC : MAX. PARTICLE SIZE 125 MM 63 mM
PASSING &lt; 10%
OR
• IF 63 mM PASSING &gt;10 %
LL &lt;45%
PI&lt;20%
(WL )
(IP )
• HOWEVER MAX. AMOUNT OF CLAY SIZE (2mm):10 % DESIGN
• HORIZONTAL AND VERTICAL STRIP SPACINGS : Sh &amp; Sv
Schlosser Mc Kittr.
• AT DEPTH Z, STRIP TENSION :
Ts = K . sv . Sh . Sv
Earth
pressure
coefficient
Calculated vertical stress
e.g. using Meyerhofs
coeff. distribution)
K for z &lt; 6 m K  K  z ( K A  K 0 )
0
6
K for z &gt; 6 m
K=KA
Ministere de Trans.
THIS IS BASED ON THE
OBSERVATIONS
OF
FULL
SCALE WALLS SF = 3 IS USED
TO
ULTIMATE
TENSILE
STRENGTH OF GALVANISED
STEEL.
BOND FAILURE
• Effective bond length is that
projecting beyond the &quot;failure
surface&quot;
• If not measured in a shear box
coefficient of friction is taken to
be 0.40 for plain strips and tan f'
for ribbed strips or 0.90 (arc tan
42) (m = atanf', a = 0.46-0.50,
plain strips 0.48 tan 40 = 0.40)
• FOR H &lt; 6 M F IS ASSUMED TO REDUCE LINEARLY FROM
UNITY AT THE FREE SURFACE TO TANf' AT A DEPTH OF 6 M.
• TAKING A FACTOR OF SAFETY OF 1.5 AGAINST BOND
FAILURE THE REQUIRED BOND LENGTH LA AT DEPTH Z IS
1.5 Ts
La 
2.b. f . z
Ministere desTransports 1979
LA IS ≥ 0.8H OR ≥5 M WHICH EVER IS GREATER.
THIS IS INTERNAL STABILITY. THE STRUCTURE
MUST BE CHECKED FOR EXTERNAL STABILITY.
LET US GO THROUGH THE STEPS.
I.
CHECK STABILITY OF EACH LAYER BY
CALCULATING THE MAX. TENSILE FORCE T. PER
METER RUN OF WALL TO BE RESISTED IN ith
LAYER. THIS FORCE IS TAKEN TO BE THE SUM OF
THE TENSIONS CREATED BY FIVE POSSIBLE
Ti  T1  T2  T3  T4  T5
Due to
KA..zi
Due to
surcha
rge q
Due to strip
top of wall
Due to
horizontal
top
Due to
bending
moment
cause by
external
wall
II. HAVING EVALUATED Ti CHECK TENSILE FAILURE &amp; PULL - OUT
FAILURE
F.S.
2.Ti
Pi 
 .Li .( .zi  q)
Required
reinforcement
perimeter per
meter run of wall
total length of each
reinforcement in the
ith layer.
III. ONCE THE STABILITY OF EACH AND EVERY LAYER OF
REINFORCEMENT HAS BEEN CHECKED THE OVERALL
STABILITY OF SEVERAL TRIAL WEDGES IS CHECKED USING
A GRAPHICAL METHOD.
m
1
T   . pi .Lai .( .zi  q)
2
Effective bond length
```