4.5 REINFORCED EARTH (terre armee)

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4.5 REINFORCED EARTH (terre armee)

• FILLS CAN BE FORMED PLACING "REINFORCEMENTS" IN
  THEM AND COMPACTING (GLASS FIBRE REINFORCED,
  PLASTIC FIBRE, TRYLENE FIBRE, FLEXIBLE GALVANISED
  STEEL STRIPS ETC.) ( 5 MM THICK 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.

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• 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 gt10
• LL lt45 PIlt20
• (WL ) (IP )
• HOWEVER MAX. AMOUNT OF CLAY SIZE (2mm)10 DESIGN

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• HORIZONTAL AND VERTICAL STRIP SPACINGS Sh Sv
  Schlosser Mc Kittr.
• AT DEPTH Z, STRIP TENSION
• Ts K . sv . Sh . Sv Ministere
  de Trans.
• K for z lt 6 m
• K for z gt 6 m KKA

Earth pressure coefficient
Calculated vertical stress e.g. using Meyerhofs
coeff. distribution)
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• 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 "failure surface"
• 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)

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• 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

Ministere desTransports 1979
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• 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 LOADINGS.

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Due to bending moment cause by external loading
on wall
Due to KA.g.zi
Due to surcharge q
Due to horizontal loading at top
Due to strip loading at top of wall
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• II. HAVING EVALUATED Ti CHECK TENSILE FAILURE
  PULL - OUT FAILURE

F.S.
total length of each reinforcement in the ith
layer.
Required reinforcement perimeter per meter run of
wall
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• 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.

Effective bond length
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