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Geosynthetic Reinfored Soil Structures

By

Satish Naik

Historical Perspective

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Evolution Of Soil Reinforcement

Ribbed Steel Strip – The First Engineered Soil Reinforcement

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Welded Steel Ladders

Extruded HDPE Geogrid

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Uniaxial Woven Geogrid

Knitted Geogrid

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Polymeric Straps

Concept of Soil Reinforcement

Courtesy of Strata Geosystems

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Reinforced Soil Design

1-16

Components of an Reinforced Soil Wall

Finished Grade

Reinforcements

Retained

Backfill

Facing

Foundation Soil

Original Ground

Limits of Excavation

Mechanically Stabilized Earth

Mass

Leveling Pad Drainage

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External Stability Modes

External Stability Modes

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External Stability Modes

Pullout of the Reinforcement

Anchorage Length

Internal Stability Modes

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Overstressing in the Reinforcement

STRESS

STRESS

STRESS

STRESS

STRESS

STRESS

Internal Stability Modes

Global Mode Of Failure

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Geogrid – Properties & Testing

Allowable Design Strength

Purpose - Define material properties and reduction factors for determination of allowable design strength, Ta:

Ta = Tult RFCR x RFDUR x RFID x FSUNC

Reference Reinforced Soil Slopes – FHWA

Segmental Retaining Walls – NCMA

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Required Geogrid Testing

Tensile Strength

Long-term Creep

Chemical & Biological Durability

Installation Damage

Pullout Resistance in Soil

SRW Facing Connection

Wide-Width Tensile Tests - ASTM D4595

Wide width Tensile Strength

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Creep Factor

Reduction Factor for Installation

Damage, RFID

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Pullout Resistance in Soil Soil Interaction Coefficient Ci

Connection Properties (Panel)

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Connection Properties (Panel)

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TENSILE LOAD vs DISPLACEMENT

0

10

20

30

40

50

60

70

80

90

100

110

120

0 10 20 30 40 50 60 70

DISPLACEMENT (mm)

TE

NS

ILE

LO

AD

(k

N/m

)

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CONNECTION STRENGTH vs NORMAL LOAD

Tcp = Wu*tan (14.4°) + 81.2 (kN/m)

Tsc = Wu*tan (39.4°) + 1.4 (kN/m)

0

10

20

30

40

50

60

70

80

90

100

110

120

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0

NORMAL LOAD (kN/m)

CO

NN

EC

TIO

N S

TR

EN

GT

H (

kN

/m

Geogrid Soil Retention Systems Segmental Block Wall – Segmental Block faced reinforced soil wall is a composite system consisting of Block units in combination with a mass of reinforced soil stabilised by horizontal layers of Geogrid.

Panel Faced Wall – Panel faced wall is a reinforced concrete panel faced reinforced soil wall system of T and square shape.

Stabilised Slopes – This is an environment-friendly green-faced solution, can substantially increase the usable land for change-of-grade applications. They are further divided into stiff faced slopes from 45 to 70°and soft faced slopes less than 45°

Mesh Faced Walls – This is an environment-friendly stone facedn-faced solution, Can be of both gabion faced as well as with welded steel mesh facing.

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Schematic representation of Panel faced Reinforced Soil Wall

Panel Faced Reinforced Soil Walls

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Moradabad Bareilly Expressway

Fly-ash can also be used as a reinforced backfill

ROB at Khaperkheda TPS

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Fly Ash spread on the approach

Aerial view of approach

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Geogrid soil reinforcement spread and pinned

Geogrid connection to panel

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Heavy rolling of Fly Ash Fill

Light rolling at edges and corners

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Geogrid awaiting backfill placement

Completed and capped structure

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Block faced reinforced soil wall

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Block Faced Walls, NH-8 Gujarat

Between Mumbai & Ahmedabad

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Gabion Face Geogrid

Reinforced Walls

Gabion Faced Geogrid Reinforced Soil Bridge Retaining Wall

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The direction along which

Geogrid has to be laid for

reinforcement

Shillong Bypass Project, NHAI- Meghalaya

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Gabion faced walls at Lodha Splendora, Thane

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85 degree Steel Mesh Faced Wall

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Steel Mesh Faced Reinforced Soil Slope – up to 70°

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PrimaryReinforcement

IntermediateReinforcement

6 ft Maximum12"-18"Typical

4 feet

Slope Face(surface vegetationrequired)

< 45 degrees

Soft Faced Reinforced Soil Slope

Geogrid Reinforced Slope

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Shillong Bypass Project, NHAI- Meghalaya

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Composite Structure With

A. Gabion Base and Reinforced Soil slope with

Reinforced Soil Wall / Slope on the top

B. Stabilised rear cut face with Soil Nails with a

Reinforced Soil front facing

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Shored Reinforced Soil Walls

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Composite Structure With A Gabion

Base

Wadi-Umti Recharge Dam

Sultanate of Oman

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Biaxial Geogrid

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Roads on Weak Soils

weak soil

Penetration of coarser sub base course particles into weak subgrade on loading

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Application of Biaxial geogrid

Granular material compacted over biaxial geogrids partially penetrates and projects through the apertures creating a strong and positive interlocking

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weak soil

Biaxial

geogrid

weak soil

More effective load distribution enables heavier loading Biaxial

geogrid

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Embankment over Soft clay usage of Biaxial Geogrid or High Strength Woven Geotextile

Reinforcement:

Full width or

localised areas

Soft Clay Foundation

Embankment Fill

Reinforcement

tension develops as

a vector of these forces

IRC-113-2013-Geosynthetic Reinforced Embankment on Soft Soils

Glass Fibre Geo-composite

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asphalt layer (overlay)

Underlying asphalt pavement

Glassfibre Geogrid

Non-woven Geotextile

Asphaltic Reinforcement

Glass fiber geogrid composite is a high-strength, low strain composite of glassfibre reinforcement and a non-woven geotextile

Laying of Asphaltic Reinforcement

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Repairs & Rehabilitation Of

Reinforced Soil Structures

Project in Gujarat

Height of RSW was ranging from 2.0 m to 9.0 m

Soil investigation was carried out to assess the

bearing capacity of foundation soil

Results of SPT test result showed abrupt variation

from 7 to 21 indicating erratic ground condition

Uncontrolled filled soil was encountered with depth

varying from 1.5m to 3.5m

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Ground Improvement

Replacement of top layer of uncontrolled fill with

well-compacted granular soil was decided

Wall with height up to 5.0 m was built on natural ground

without any treatment after providing required

embedment.

For wall with higher height, geotextile reinforced well

compacted granular soil was used. H

eigh

t of

the

RS

wal

l

G.L.

Em

bedm

ent

dept

h

Length of the geogrid

Reinforced Soil Zone

2500

200

1500

Woven geotextile

Wrap around

Section for 5.0m to 7.0m height of wall

well compacted granular soil

Proposed ground improvement for wall with height ranging from 5.0m to 7.0m

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Hei

ght

of t

he

R. E

. wal

l

G.L.

Em

bed

men

t d

epth

Length of the geogrid

Reinforced Soil Zone

2500

200

1500

Woven geotextile

Wrap around

Wrap around

15002001500

Section for 7.0m to 9.0m height of wall

Well compacted granular soil

Proposed ground improvement for wall with height ranging from 7.0m to 9.0m

Effect Of Severe Rains

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Effect Of Severe Rains

A stretch of 20 m of partly built wall of only 7 blocks

(1.421 m) subsided with the subsidence at its highest

being 550 mm.

The reinforcing geogrid was 8.3 m long and placed in

two layers as per design

The wall face had opened up and the leveling pad exposed

It had cracked at many places indicating subsidence

Effect Of Severe Rains

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Investigation of failure

DCPT test were conducted at the site of failure

DCPT-values less than 4 reflect marginal to poor

compaction

DCPT-values above 6 indicate medium to better

compaction

DCPT – RESULT

CONDUCTED TO

CHECK COMPACTION

STATE OF REPLACED

SOIL

DCPT-Structure-2

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

0 10 20 30 40 50 60 70 80

DCPT-N-value

Dep

th (

m)

DCPT N value

after replacement

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Solution

DCPT value indicated that proper densification was not achieved.

With further observation beyond 2.5 m depth, competent soil strata was identified.

Densification of replaced fill with sand/stone pile was considered and implemented

Proper densification was verified by DCPT test before installation of RSW

Densification with Stone Piles

G.L.

H

1000

300

3500

REINFORCED SOIL WALL

REPLACED FILL

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DCPT value

All DCPT-value are greater than six showing proper densification.

Structures are performing satisfactorily for Ten years despite the heavy traffic load of NH-8

DCPT-Structure-2

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

0 10 20 30 40 50 60 70 80

DCPT-N-value

Dep

th (

m)

AFTER DENSIFICATION WITH STONE PILES

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FINISHED PROJECT

Facing connection failure

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Soil nailing at centre of panel

Connecting bolt failure

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Connection details

Nailing for re-attaching facing

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Bulging of panel joints

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No reinforcement on top of wall

Missing top reinforcement

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Repairs

Dimensional Tolerances

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All defects possible

Details

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Improper Backfill

Large boulders

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No drainage media

Geogrid exposure & vandalism

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Effect of flowing water

Failure due to excess pore pressure buildup

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Slide At Toe Of Wall

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Global stability failure

Some Other Precautionary Measures

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Levelling pad step

Foundation Too High

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Direction of geogrid laying

Backfill too low

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Reinforcement too low

Thank You