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GEOSYNTHETICS AND REINFORCED SOIL STRUCTURESREINFORCED SOIL STRUCTURES

Different Types of Different Types of Geosynthetics and Their

Applications

K. Rajagopal, ProfessorDepartment of Civil EngineeringDepartment of Civil Engineering

IIT Madras, Chennaie-mail: gopalkr@iitm ac ine mail: gopalkr@iitm.ac.in

RECAP OF PREVIOUS LECTURERECAP OF PREVIOUS LECTURE

• Introduction• Introduction• Historical background• Early applications• Functions of geosynthetics• Functions of geosynthetics• Types of geosynthetics

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OUTLINE OF 2nd LECTUREOUTLINE OF 2 LECTURE

• TYPES of geosynthetics• TYPES of geosynthetics- - - - CONTINUED

• TYPICAL APPLICATIONS

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TYPES OF GEOSYNTHETICS

• GeotextilesG id• Geogrids

• Geonets• Geomembranes• Pre-fabricated vertical drains (PVD)Pre fabricated vertical drains (PVD)• Geosynthetic Clay Liner (GCL)

G ll (3 d fi t)• Geocells (3-d confinement)• Geocomposites & Geo-others

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GEONETSGEONETS• Geonets are also planar products• Consists of ribs in two directions• Apertures are of diamond shape• Ribs in the two directions are at different planes• Thickness of geonets is larger than that of g g

geogrids• Geonets are also referred to as geospacersg p

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TYPICAL GEONETS

Ribs at two Ribs at two horizontal planes

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GEONET APPLICATIONS

• Erosion control – ribs act as small check dams to slow down the surface runoff – decreases erosion potentialrunoff decreases erosion potential of waterD i l fl l• Drainage layers – water flows along the geonet because of large thickness

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Boulder net laid on Konkan railway line in Western ghats – functions as guide for loose boulders and vegetation support

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Laying of boulder net

Vegetation growth after two seasons

Courtesy: M/s Garware Wall Ropes Ltd., Pune

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Anchor trench at the top of the slope 1m deep 0 5mthe slope, 1m deep, 0.5m wide, filled with soil

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GEOMEMBRANES

• Thick impervious plastic sheets• Thickness 5 mm to 3 mm approximately• Thickness .5 mm to 3 mm approximately• To contain liquids and gases

Ro gh s rface te t re Smooth do ble sided membraneRough surface texture Smooth – double sided membrane

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APPLICATIONS OF GEOMEMBRANESGEOMEMBRANES

• Landfill lining• Landfill lining• Canal lining• Tunnel lining

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Geomembrane in a landfillGeomembrane in a landfill

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Canal lining using geomembranes

geomembrane Anchor trenchConcrete lining of surface

g Anchor trench

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Tunnel lining for moisture t tiprotection

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Pre-fabricated vertical drainst l t th lid ti to accelerate the pre-consolidation

of soft clay soils

cT vt %)(UfT

dcT v

v 2 )(fT v

T = time factor

dTd

2

Tv = time factort = timecv = coefficient of

lid ti

cdT vt consolidation

d = drainage path lengthU% = degree of consolidationcv

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Reducing the flow path length to accelerate rate of consolidationaccelerate rate of consolidation

surcharge fill

Highly permeabledrainage drainage medium

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PVDs for pre-consolidationPVDs for pre consolidation

Corrugated plastic core for drainage

L

tt

Geotextile filter

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Pore water flows laterally

Connection arrangements for wick

Pore water flows laterally to the wick drains and is carried through the core

drain installation

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Installation of PVDs at a construction site – notice the ti f PVD ith th h l tconnection of PVD with the anchor plate

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PVD b i h d i t th dPVD being pushed into the ground21/52Types and Functions of Geosynthetics

General view after installation of PVD’s at a siteGeneral view after installation of PVD s at a site22/52Types and Functions of Geosynthetics

Geosynthetic Clay Liners

• Consist of a core of bentonite clayConsist of a core of bentonite clay sandwiched between layers of thick non-woven geotextileg

• Applied below and above geomembranelayers in landfillsy

• Self-repair mechanism• Bentonite expands when flid leaks throughBentonite expands when flid leaks through

punctured geomembrane – closes the gap

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Geosynthetic Clay Linery yGeotextile layers

dry bentonite ypowder

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GEOCELL – 3d confinement product

Iso-metric view of a

Plan view showing the mechanism of confinement

geocell layer

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Photograph of an expanded geocellPhotograph of an expanded geocell26/52Types and Functions of Geosynthetics

AdvantagesAdvantages• Easy to transportEasy to transport• Any fill material can be used

All d fi t t il• All round confinement to soil• Semi-rigid layer (very stiff support)• Spreads loads over a large area• Excellent support even under cyclic loadsExcellent support even under cyclic loads.

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APPLICATIONSAPPLICATIONS

• Erosion controlErosion control• Steep slopes and retaining walls

S b b t• Sub-base support• Road bases

R il t k• Railway tracks• Container yards

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Use of geocells for construction of unpaved road Factory

P ti f dStapling to join Stretching of the geocell layerPreparation of groundS ap g o jodifferent geocells

Stretching of the geocell layer

Stone aggregate filled in geocell pockets Compaction by a 10 tonne rollerStone aggregate filled in geocell pockets Compaction by a 10 tonne roller

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Geocells used for construction of a steep slope

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Vegetation taking root through geocell pockets

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IITM students standing on a geocell supported soil

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Typical Container yard – heavy loads, usually constructed on soft marine clays near the shorey

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Typical mud wave formation in container yards due to heavy l d d t l ft b d illoads and extremely soft subgrade soil

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Geotextile separator being laid on the ground surface at a container yard

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Geocell layer laid on the geotextile separator and filled with stone aggregate

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Container yard 3 years after geocell treatmenttreatment

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Some more pictures of the same yard

Perfectly level surface – minor damage in paver blocksy g p

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Polymeric erosion control mats

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GeocompositesC bi ti f t diff t t f• Combination of two different types of geosynthetics to take advantage of each

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Geo-others• Geodrains• Lightweight fillsLightweight fills• Geopipes

G t til b & il l ti• Geotextile bags & soil encapsulation• Gabions• Geosynthetic Encased Stone Columns• Many others – left to the imagination ofMany others left to the imagination of

engineers

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Drainage boards for use in Retaining WallsDrainage boards for use in Retaining Walls

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Light-weight fill cum drainage medium

Thi k di d f l t b dThick medium made of polystyrene beads43/52

Types and Functions of Geosynthetics

Gabions filled with stones

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Gabions filled with sand bags

SAND FILLED GEOBAGS PLACEMENT OF GEOBAGS

TYING OF ROPE GABIONS FINAL VIEW45/52

Types and Functions of Geosynthetics

Light-weight drainage medium

Made of used rubberMade of used rubber tyres and other industrial wastes

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Bearing capacity enhanced byEncased Stone Column

Bearing capacity enhanced by

Passive

Geosynthetic Additi l

Passive pressure

+ yencasementAdditional

confinement

Stone column

Sectional plan

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Construction of Encased Stone ColumnConstruction of Encased Stone Column

Al i t l (2005)Alexiew et al. (2005)48/52Types and Functions of Geosynthetics

Courtesy:Dipl.-Ing. Holger Pohlmann

Naue Fasertechnik GmbH & Co. KG

P dPresent study

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Load settlement curve for stone columns encased in non-woven geotextileencased in non woven geotextile

0 100 200 300 400Pressure (kPa)

0

10

ESC - 50 mmESC - 75 mm

10

20t (m

m) ESC - 100 mm

OSC - 50 mmOSC - 75 mmOSC - 100 mm

30

ettle

men Clay

40

50

Se

5050/52Types and Functions of Geosynthetics

Latest TrendsLatest Trends

• Vacuum consolidation• Vacuum consolidation• Encased stone columns• Electro Kinetic geosynthetics

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