ppt o osils
TRANSCRIPT
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INTRODUCTION
&
DESIGN OF REINFORCED
SOIL REATINGING WALL
Geosynthetics andSoil Reinforcement
Hari Kishore .K.
Summer Trainee ,IITH
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GEOSYNTHETICS
Artificial fibre used in conjuction with soil to
improve its performance
CLASSIFICATIONGeotextilesgeomembranes
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Applications in civil engineering
Seperation
Filtration
Drainage
Soil Reinforcement
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Soil Reinforcement
It improves response of the soil by
increasing normal loading and reducing
disturbing shear forces
Used in:
sinkholes
Matresess in foundation
Steep slopes
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Design principle of reinforced soil
structures
External stabilized system
Internal stabilized system
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Mechanism of reinforced soil
3
1
v
hr/2
3
1
vr
Without reinforcement with reinforcement
h/2
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Deformations are restrained due to friction
betwen soil and reinforcement
Shear stress at interface generates tenslie
force in reinforcement
Two types of failures:
Slip failure
Rupture failure
F t ff ti b h i d
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Factors affecting behaviour and
performance of reinforcement
1.Reinforcement
Forms
Surface propertiesStiffness
Stress strain response study
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2.Soil
Index properties gradations arerequired
Cohesionless soils are preferredMaterial properties as per BS 8006 (1995)
Density
Grading
Uniformity coefficient (cu) {> or equal
to5} Angle of internal friction (){25
degrees}
Coefficient of friction between fill and
reinforcement
DESIGN OF REINFORCED
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DESIGN OF REINFORCED
RETAINING WALLS
Enhancement of shear strength
Unit cell tests
Direct shear box test
Normal component of reinforcement force
adds friction
Tangential component resist shear loading
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Available reinforcement force:
To achieve equilibrium,
mobilized shear strength +reinforcement force =
applied shear loading
Limiting conditions for magnitude of reinforcement
force:
Tensile strength of the reinforcement
Bond stress between reinforcement and soil
Compatibility of tensile strains between
reinforcement and soil
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Components of RS wall
Reinforcement:
Steel or plastic
Steel susceptible to corrosion
Recently HDPE polymers areused
Facing:
Facing units carry little or no loads To stop erosion and to provide
architectural finish
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Types of facings:
Discrete panels Full height panels
Wraparound facing
P i i l f d i
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Principles of design
Two types of stability checks :
External stability (governs reinforcement
length)
Internal stability (governs reinforcement
spacing)
D i d
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Design procedure:
Initial size of structure External stability check
Type of reinforcement
Internal stability check
Design of connections
As per BS 8006 (1995)
Steps in design:
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Preliminary dimensions
Depth of foundation = 10% of height of
backfill(h).
Total height (H)= 1.1times of backfill height (h).
Length of reinforcement should be 0.8 times ofH
As per BS 8006 (1995)
Factor of safety:
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Factor of safety:
Similar to conventional retaining wall design, factor ofsafety's are given for loading and resistance.
As per BS 8006 (1995) four factor of safteys
are used. manufacture(fm11) 1.05
Extrapolation(fm12) 1.08
Susceptibility (fm22) 1.08
Environment(fm21) 1.08
E t l t bilit
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External stability
Sliding: Starts from unreinforced portion
Due to lack of proper friction between soil
and reinforcementF.S=V/H
Minimum value of F.S is 2
Overturning:
It is initiated by thrust of unreinforcedbackfill
F.S = resisting moments (MR)
overturning moments (Mo)
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Bearing failure:
Bearing failure occurs if:
Maximum vertical stress> S.B.C of soil.
Mohr's distribution:
Traditional trapezoidal distribution is changed
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Internal stability
TENSION FAILURE:
When the tensile capacity of reinforcement is less
PULLOUT FAILURE:
When the length of reinforcement is less or lack offriction
Types of failures:
T i f il
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Tension failure will occur if reinforcement strength isinsufficient to carry horizontal loads
Tension failure checked for each layer taking intoaccount the self weight of fill and everything over it assurcharge.
Earth pressure theories are usedSpacing of reiforcement
Tension failure
Pull out failure
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Pull out failure
Wedge mechanism
Assumptions
Forces
Length of reinforcement
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Advantages:
Reduction in earth works
Ease of constructionSpeed
Usability of poor fill materials