Geosynthetics a Civil Engineering Construction Material

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Geosynthetics - A Civil Engineering ConstructionEngineering Construction

Material

Braja M DasBraja M. Das

Mechanically Stabilized Earth — MSE

• Composite material with compacted fill strengthened byinclusion of tensile elements:– Metal rods / strips– Metal rods / strips– Geosynthetics

• Geotextiles• Geogrids

• French engineer Vidal (1966) ― initiated presentconcept for systematic analysis and designp y y g

• Since 1966, MSE structures ― retaining walls andembankments over soft soil and steep slopes ―built all over the world.

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Retaining Walls with Metallic StripReinforcement

Reinforced-earth walls areflexible walls.e b e a s

Main components:

● Backfill ― granular soil

● Reinforcing strips —thin, wide strips placedat regular intervalsg

● A skin or cover on thefront of the wall

GEOSYNTHETICS

According to ASTM D4439, a geosynthetic is defined asa planar product manufactured from polymeric materialused with soil, rock, or other geotechnical engineering

l t d t i l i t l t f h drelated material as an integral part of a human-madeproject, structure, or system.

Polymers used: Polypropylene (92%) Polyethylene (2%) Polyamide (nylon) (1%) Polyester (5%)

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Identification of the Usual Primary Function for Each Type of Geosynthetic

Geotextiles

• Woven geotextiles — made of two sets of parallelWoven geotextiles made of two sets of parallelfilaments or strands of yarn systematically interlaced toform planar structure

• Knitted geotextiles — formed by interlocking a seriesof loops to one or more filaments of strands of yarn toform planar structuresform planar structures

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• Nonwoven geotextiles — formed from fibers orfilaments arranged in oriented or random pattern inplanar structure

– Filaments (or short fibers) arranged in a loose web inth b i i th b d d b bi ti fthe beginning, then bonded by one or combination of:

• Chemical bonding – by glue, rubber, latex, acellulose derivative, or the like

• Thermal bonding – by heat for partial melting offilaments

• Mechanical bonding – by needle punching

• Needle-punched nonwoven geotextiles — thick; havehigh in-in-plane permeability

Geogrids

A polymeric (i.e. geosynthetic) material consisting ofconnected parallel sets of tensile ribs with apertures ofsufficient size to allow strike-through of surrounding soilsufficient size to allow strike-through of surrounding soil,stone, or other geotechnical material

Primary Functions:

Reinforcement

Separation Separation

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In the 1950s, Dr. Brian Mercer (1927-1998) developedthe Netlon® process in which plastics are extruded intoa net-like process in one stage. In 1959, he foundedNetlon Ltd. in the United Kingdom to manufacture the

d tproduct.

Based on Dr. Mercer’s further innovative research anddevelopment work on extruded net technology, somepolymer straps and strips were formed into grid-likeproducts during the 1970s.

The first integral geogrids were developed in the late1970s and first employed in various applications in theearly 1980s.

In the early stages of development of geogrid,several universities in the United Kingdom wereheavily involved in a comprehensive program ofheavily involved in a comprehensive program ofresearch that examined the polymer technology.

These universities were Leeds, Nottingham, Oxford,Sheffield and Strathclyde.

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Initial Extruded Geogrid Developed by Netlon ®

Two types: Biaxial

Uniaxial

Geogrids

Biaxial Geogrid

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Geogrids

Uniaxial Geogrid

Commercially Available Geogrids

• Extruded —Formed using a thick sheet of polyethylene orpolypropylene that is punched and drawn to createp yp py papertures and to enhance engineering properties ofresulting ribs and nodes

• Woven —Made by grouping polymeric—usually polyester orpolypropylene—and weaving in a mesh pattern thatis then coated with a polymeric lacquer

W ld d• Welded —Made by fusing junctions of polymeric strips. Haveshown good performance when compared to othertypes of pavement reinforcement applications

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Geogrids

• Rib thickness—0.5 to 1.5 mm

• Junction thickness—2.5 to 5.0 mm

• Aperture size—25 to 150 mm

• Open area of grids—50% or more of grid area

• Develop reinforcing strength at low strain levels (such as 2%)( )

Triaxial Geogrid

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How do geogrids reinforce?

Reduction of ɛhPrevention of lateral spreading of material above geogrid

Increase of lateral confinementIncrease of h

Increase of lateral confinement and hence increase of stiffness and modulus

Reduction of ɛvLess deformation of granularmaterial

B d i f ti l tReduction of v

Broadening of vertical stress distribution

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Geomembranes

High-density polyethylene (HDPE), linear low-

density polyethylene (LLDPE), and flexible

polypropylene (PP) geomembranes are

manufactured by an extrusion method.

Major Applications of Geotextiles

Separation of Dissimilar Materials

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Major Applications of GeotextilesReinforcement of Weak Soils and Other Materials

Major Applications of GeotextilesFiltration (Cross-Plane Flow)

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Major Applications of Geotextiles

Drainage (In-Plane Flow)

Utilization of Geotextiles in North America by Application Area

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Current Uses of Geogrids

Current Uses of Geogrids

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Current Uses of Geomembranes

Geomembranes have been used in the following environmental, geotechnical, hydraulic, transportation, and private development applications:

Current Uses of Geomembranes

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Current Uses of Geomembranes

Current Uses of Geonets

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Current Uses of Geonets

Current geosynthetic sales are difficult to assess but the estimate forCurrent geosynthetic sales are difficult to assess, but the estimate for 2003 on a worldwide basis is as follows (note that the values are in millions of square meters and millions of US dollars).

Koerner, Robert M. (2005). Designing with Geosynthetics, Fifth Edition, Pearson/Prentice Hall, Upper Saddle River, NJ.

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Berg, Bonaparte, Anderson and Chouery (1986)3rd International Conference on Geotextiles, Vienna, Austria

Retaining Wall Construction Costs in the U.S.(Koerner et al., 1998)

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Full-Scale Test on Geogrid-Reinforced Retaining Wall under

Earthquake Conditions

Full-scale reinforced soil retaining wall

Conducted by SEC-Atom Dinamic nearVyborg in Russia – June 2009

Full-Scale Test on Geogrid-Reinforced Retaining Wall under Earthquake Condition

Height 3.5m with sand backfill and TW1 facing blocks(23 blocks high) giving 86 face inclination(23 blocks high) giving 86 face inclination

Reinforced with 8 layers of geogrid (3m = 0.86H)

Test wall constructed on large shaking table

Total weight of sand and facing around 100t

Extensive monitoring to measure deformation and soilpressure

Loads applied in 6 “earthquakes” (EQ1 to EQ6)

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Monitoring

Instruments

Acceleration

Deflection

Earth Pressure

Sand fill

Actuator3.5m

Shaking table

Supporting frame Pneumatic cushions

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During Construction

Construction Completed

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Construction Completed

op5: 6/16/2009 14:44:43 1 kHz 15.9 s 15900 samples5

4.0

3.5

3.0

2.5

2.0

Vertical acceleration record during EQ5

A3

0.5

m/s

2

2.0

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

0 2 4 6 8 10 12 14Time, s From: 0 s To: 15.899 s Samples: 1-15900

-2.0

-2.5

-3.0

-3.5

-4.0

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op5: 6/16/2009 14:44:43 1 kHz 15.9 s 15900 samples

6.0

5.5

5.0

4.5

4 0

Horizontal acceleration record during EQ5

A4

0.5

m/s

2

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0 2 4 6 8 10 12 14Time, s From: 0 s To: 15.899 s Samples: 1-15900

0.0

-0.5

-1.0

-1.5

-2.0

2 5

Sand fill

Device to measure lateral deflection at each block (1 – 22)

Actuator3.5m

Shaking table

each block (1 22)

Supporting framePneumatic cushions

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Instrument to Measure Deflection

Instrument to Measure Deflection

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op5: 6/16/2009 15:06:59 1 kHz 15 s 15000 samples

P16

2 m

m

2

0

-2

-4

0

Blocks 16 to 20 during EQ5

P17

2 m

m

-2

-4

P18

2 m

m

2

0

-2

-4

m

2

0

0 2 4 6 8 10 12 14Time, s From: 0 s To: 14.999 s Samples: 1-15000

P19

2 m

m

-2

-4

P20

2 m

m

2

0

-2

-4

op5: 6/16/2009 15:06:59 1 kHz 15.1 s 15100 samples

P11

1 m

m

1

0

-1

1

Blocks 11 to 15 during EQ5

P12

1 m

m

0

-1

-2

P13

1 m

m

1

0

-1

-2

1

0

0 2 4 6 8 10 12 14Time, s From: 0 s To: 15.099 s Samples: 1-15100

P14

1 m

m

-1

-2

P15

2 m

m

2

0

-2

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22

0 1 2 3 4 5 6 7 Deflection (mm)

k

Start

H = 0

V = 01

Blo

ck

0 4

0.8

on

(g

)

Horizontal

-0.8

-0.4

0

0.4

Ac

ce

lera

tio

Vertical

Test Sequence

Earthquakeevent

kh kv

12345

0.240.420.500.550 59

0.270.620.600.750 255

60.590.63

0.250.70

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Animation of Wall Facing Movement during Earthquakes

Dark brown line shows wall position on Dark brown line shows wall position onapplication of load

Fine orange line shows previous location

Large red arrow shows direction ofmovement

Lower graph gives simplified record of theearthquakes

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0 1 2 3 4 5 6 7 Deflection (mm)

k

EQ1

H = 0.24g

V = 0.27g

0 4

0.8

n (

g)

Horizontal

1

Blo

ck

-0.8

-0.4

0

0.4

Ac

ce

lera

tio

Vertical

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22

0 1 2 3 4 5 6 7 Deflection (mm)

ck

After EQ1

H = 0

V = 0

0.4

0.8

on

(g

)

Horizontal

1

Blo

c

-0.8

-0.4

0

0.4

Ac

ce

lera

tio

Vertical

22

0 1 2 3 4 5 6 7 Deflection (mm)

k

EQ2

H = 0.42g

V = 0.62g1

Blo

ck

0.4

0.8

on

(g

)

Horizontal

-0.8

-0.4

0

0.4

Ac

ce

lera

tio

Vertical

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22

0 1 2 3 4 5 6 7 Deflection (mm)

k

After EQ2

H = 0

V = 01

Blo

ck

0 4

0.8

n (

g)

Horizontal

-0.8

-0.4

0

0.4

Ac

ce

lera

tio

n

Vertical

22

0 1 2 3 4 5 6 7 Deflection (mm)

EQ3

1

Blo

ck

EQ3

H = 0.50g

V = 0.60g

0.8

(g)

Horizontal

-0.8

-0.4

0

0.4

Ac

ce

lera

tio

n Horizontal

Vertical

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Aft EQ3

22

0 1 2 3 4 5 6 7 Deflection (mm)

ck

After EQ3

H = 0

V = 01

Blo

0 4

0.8

n (

g)

Horizontal

-0.8

-0.4

0

0.4

Ac

ce

lera

tio

n

Vertical

EQ4

22

0 1 2 3 4 5 6 7 Deflection (mm)

ck

EQ4

H = 0.55g

V = 0.75g1

Blo

c

0 4

0.8

n (

g)

Horizontal

-0.8

-0.4

0

0.4

Ac

ce

lera

tio

n

Vertical

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Aft EQ4

22

0 1 2 3 4 5 6 7 Deflection (mm)

ck

After EQ4

H = 0

V = 01

Blo

c

0.4

0.8

on

(g

)

Horizontal

-0.8

-0.4

0

Ac

ce

lera

tio

Vertical

EQ5

22

0 1 2 3 4 5 6 7 Deflection (mm)

ck

EQ5

H = 0.59g

V = 0.25g1

Blo

c

0.4

0.8

on

(g

)

Horizontal

-0.8

-0.4

0

0.4

Ac

ce

lera

tio

Vertical

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Aft EQ5

22

0 1 2 3 4 5 6 7 Deflection (mm)

ck

After EQ5

H = 0

V = 01

Blo

0.4

0.8

on

(g

)

Horizontal

-0.8

-0.4

0

Ac

ce

lera

ti

Vertical

Q

22

0 1 2 3 4 5 6 7 Deflection (mm)

ck

EQ6

H = 0.63g

V = 0.70g1

Blo

0.4

0.8

on

(g

)

Horizontal

-0.8

-0.4

0

Ac

ce

lera

tio

Vertical

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After EQ6

22

0 1 2 3 4 5 6 7 Deflection (mm)

ock

0.4

0.8

ion

(g

)

Horizontal

After EQ6

H = 0

V = 01

Blo

-0.8

-0.4

0

Ac

ce

lera

t

Vertical

Facing after Completion

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Facing after Completion

• Indication of small permanentsmall permanent deformation after the test

• Small gap between top of fill and facing blocksand facing blocks

Conclusions

Considerations for Seismic Design

Minor shaking: Static design adequate

Moderate shaking:

Grid layout from static design adequate—grid may be longer

Strong shaking: Both length and grid layoutStrong shaking: Both length and grid layout likely to be determined by seismic forces

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Thanks to Tensar International for providing the slides for full‐scale seismic tests on retaining wall in Russia.