FHWA-NHI-10-024 Design & Construction of MSE Walls and Reinforced Soil Slopes - Volume II
Reinforced soil walls-1 · 2017. 8. 4. · Geosynthetics and Reinforced Soil Structures Reinforced...
Transcript of Reinforced soil walls-1 · 2017. 8. 4. · Geosynthetics and Reinforced Soil Structures Reinforced...
Geosynthetics and Geosynthetics and Reinforced Soil Structures
Reinforced Soil Walls
Prof K RajagopalProf K. RajagopalDepartment of Civil Engineering
IIT Madras, Chennaie-mail: [email protected]
Outline of the LectureOutline of the Lecture
• Need for retaining wallsNeed for retaining walls
• Types of Retaining Walls
i f d il• Reinforced soil
• Reinforced Soil Walls
• Advantages
• Various configurationsVarious configurations
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Need for Retaining WallsS il h hi h i h b li i d• Soil has high compressive strength but limited tensile and shear strengths
• Can stand on its own only up to its own angle of• Can stand on its own only up to its own angle of repose
• Steeper slopes require lateral supportSteepe s opes equ e ate a suppo t• Purpose of the retaining walls is to provide lateral
support to the soil to make it stand at steep anglesInitial soil position with steep slope
Final slope at angle of repose
cv
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Types of Retaining Walls• Gravity Walls – masonry, crib walls, gabion walls, etc.• Reinforced Concrete walls – Cantilever, counterfort, buttressed
walls• RC Walls with shear keys• Sheet Pile walls
A h d Sh t Pil W ll• Anchored Sheet Pile Walls• Braced sheet pile walls• Diaphragm walls• Reinforced Soil Retaining Walls• Anchored Reinforced Soil Walls• Soil Nailed walls driven nails screw nails pre stressed nailed• Soil Nailed walls – driven nails, screw nails, pre‐stressed nailed
walls, etc.
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• Gravity walls – easy to construct, can be constructed even in remote areas using lowconstructed even in remote areas using low technology, not suitable for retaining soils higher than about 2 to 3 m.than about 2 to 3 m.
• Reinforced Concrete Walls – can be used for moderate heights to about 6 to 10 m. Beyond thatmoderate heights to about 6 to 10 m. Beyond that height, the size of the members increases rapidly.
• The foundation pressures could be very highThe foundation pressures could be very high leading to expensive foundation treatments.
• During seismic events, large inertial forces areDuring seismic events, large inertial forces are produced. Most RC concrete structures fail during earthquakes due to lack of ductility or rigidity.
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Some early concepts
Pre-cast concrete ties with
Selected stone aggregate
panels 1.5mx 0.8m
anchors
1 Ordinary soil fill
2
1
Coyne (1927) retaining wall at Brest, France - concrete panels can slide down relative to each other due to settlements, ties attached with anchors to develop passive resistance. In 1945, he built some similar
alls itho t anchors Notice that stone aggregate as sed to gi e
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walls without anchors. Notice that stone aggregate was used to give good resistance in anchors.
Some Early concepts
reinforcing elementselements
Front facing
Sectional view Plan ViewMunster (1925), USA Earth retaining structure made of wooden logs & planks –reinforcing elements are similar to ladders Front facing is a light thin facingreinforcing elements are similar to ladders . Front facing is a light, thin facing element of wooden planks. The concept is still in vogue now, except that we use steel reinforcing meshes instead of wooden ladders. Reinforcement has sliding attachment and hence can settle down with backfill
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sliding attachment and hence can settle down with backfill.
Conventional Retaining Wallsg
Masonry gravity retaining wallReinforced concrete semi‐gravity retaining wallwall
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Secant pile wall at the bottom and nailed soil slope at the top
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p p pof the excavation
Applying pre‐stress to the nail
Deep excavation in built‐up areas
Surface treated with spray concrete after the nails are locked‐in
Reinforced Soil Walls - 1 10/22Deep excavation supported by locked‐in nails with pre‐stress
Basic Principle of Reinforced Soil
Response of unreinforced and reinforced soil to external ploading
1000
1200Reinforced
600
800
1000
i f d
Without reinforcement With reinforcement ‐ stronger and stiffer response 0
200
400unreinforced
p 00 5 10 15
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Components of reinforced soil retaining wallsReinforcement Reinforced soil block
B kfill ilF i
Reinforcement layers
Reinforced soil block
Backfill soilFacing panels
Levelling pad
Foundation soilFoundation soil
• Thin, flexible facing panels - about 180 mm thickThin, flexible facing panels about 180 mm thick• Levelling pad is usually 150 mm thick and 300-400 mm wide• Backfill soil is select non-plastic fgranular fill• Horizontal reinforcement layers• Horizontal reinforcement layers
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Henri Vidal’s Original Reinforced Earth Wall
Henri Vidal French Engineer & Architect
An early form of Reinforced E th i t l t iEarth using steel strip reinforcement and steel membrane facing
1963 : Patent filed for Reinforced Earth 13/22Reinforced Soil Walls - 1
Types of wall facings in Reinforced Soil Walls
Full‐height Panel wall
Segmental panel wall
Modular block faced wall
Geotextile wrapped retaining wall
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Chronology of Reinforced Soil WallsYear EventYear Event
1963 Reinforced Earth patented by Henry Vidal
1968 First major RE structure built in France using steel strips1968 First major RE structure built in France using steel strips
1970 First geosynthetic wall using polyester (PET) straps in France
1971 First geotextile wall using wrap around concept built in Franceg g p p
1974 First RE structure built in USA
1980 Tensar geogrids (PP and PE) developed (first geogrids in the field)
1981 First geogrid reinforced soil retaining wall in UK
1985 Polyester geogrids developed (knitted variety)1985 Polyester geogrids developed (knitted variety)
1986 First reinforced soil retaining wall built in India at Ludhiana using fly ash as the backfill – height about 9m
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2006 First geogrid manufactured in India
Different Types of ReinforcementsGeosynthetic Reinforcement
– Geotextiles– Geogrids– Polymeric Strips– Grids made of strips
Steel ReinforcementS l S i– Steel Strips
– Welded Steel meshes– Steel strips with anchors– Steel strips with anchors– Twisted steel wire mesh
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Cost comparison
(FHWA 1997)
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Differences between Reinforced soil walls and conventional walls
Item Reinforced Reinforced Soil WallsItem Reinforced Concrete Walls
Reinforced Soil Walls
Flexibility Rigid system Highly flexible
Settlements Cannot tolerate large total Can tolerate large deformations without distressSettlements Cannot tolerate large total or differential settlements
Can tolerate large deformations without distress
Maximum Height Limited to some heights Can be built to even large heights as much as 50 to 100 m
Constructability Skilled labour required Unskilled labour can be used
Pace of construction Slow because of curing requirements
As fast as the backfill soil is brought to site
Foundation requirements
Large foundation pressures – needs good foundation
Foundation is not required
Seismic response Attracts large inertial forces Highly flexible – can undergo large deformationSeismic response Attracts large inertial forces – failures due to rigidity
Highly flexible can undergo large deformation during seismic events without collapse
Variations to suit site Not possible Several varieties of configurations are possible
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a at o s to su t s teconditions
ot poss b e Se e a a et es o co gu at o s a e poss b e
Different types of wall configurations
Full-height wall S d W ll iFull-height wall Stepped Wall inWeak soils
Trapezoidal wall for very strong soils
Part-height wall Embedded wall(both sides not
Back to back walls
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connected)
Different Types of Wall Configurations
Tiered wall for very large heights
Bridge abutment wall
large heights
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44m high 4-tier wall
Recap
This lecture has introduced the need for
Recap
This lecture has introduced the need for retaining walls and reinforced soil retaining wallswalls
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