ppt o osils

8/10/2019 ppt o osils

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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



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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

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