geosynthetics a civil engineering construction material
TRANSCRIPT
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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.