GEOSYNTHETICS ENGINEERING: IN THEORY AND PRACTICE · ** Soil: grain size distribution, shear...

GEOSYNTHETICS ENGINEERING: IN THEORY AND PRACTICE

Prof. J. N. Mandal

Department of Civil Engineering, IIT Bombay, Powai , Mumbai 400076, India. Tel.022-25767328email: [email protected]

Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay

Module - 2LECTURE - 7

AN OVERVIEW OF GEOSYNTHETICS



RECAP of previous lecture…..

Introduction Geosynthetics scope and definitions

Categories of geosynthetics

Raw materials for production of geosynthetics

Composition of geosynthetics

Manufacturing of Geogrid

Different types of geosynthetics

FUNCTIONS OF GEOSYNTHETICS

Separation

Filtration

Drainage

Reinforcement

Protection (Cushion)

Barrier / containment

Erosion control


SEPARATION:

Geosynthetic can separate two layers of soil and therebyprevent intermixing.


FILTRATION:

Geosynthetics can allow water to pass across the planewhile prevent or retain the soil particles.


DRAINAGE:

Geosynthetics can allow water to pass along its plane.


REINFORCEMENT:

Geosynthetics can reinforce the soil mass and improve thestability of structures in terms of strength and deformationswith respect to unreinforced soil.


PROTECTION (CUSHION):

Geosynthetics can protect from abrasion and perforation. Asfor example, the geotextile can act as a cushion overgeomembrane and prevent or reduce any kind of damage tothe geomembrane layer during construction.


BARRIER / CONTAINMENT/ WATER PROOFING:

Some geosynthetics can be used as relatively impermeablebarrier to prevent liquids or gases. It can also be used asnoise barrier.


EROSION CONTROL:

Geosynthetics can be employed to prevent or reduceerosion of soil due to rainfall and surface water runoff.

EROSION CONTROLProf. J. N. Mandal, Department of Civil Engineering, IIT Bombay

GEOSYNTHETIC FUNCTIONAL APPLICATIONS

Geosynthetic placed between ballasts and sub-grade soil in a rail road

SEPARATION


Geosynthetic placed between aggregate and foundation soil in a paved road


FILTRATION

Geosynthetic placed between earth and gabion for filtration


Geosynthetic placed between earth and rock in an earth rock-fill dam


DRAINAGE

Geosynthetic placed in an earth fill dam as a chimney drain


Gravel wrapped with geotextile in a trench drainProf. J. N. Mandal, Department of Civil Engineering, IIT Bombay

A geotextile and a geomembrane are placed in tunnel lining system (Rock -shotcrete-geotextile-geomembrane and

concrete)Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay

REINFORCEMENT

Reinforced soil steep slope with several layers of geogrids

A wrap around facing reinforced soil wallSegmental reinforced soil

retaining wallProf. J. N. Mandal, Department of Civil Engineering, IIT Bombay

PROTECTION

Geosynthetic containing sand, rock to protect against scouring

Geosynthetic placed around pile jacketing


BARRIER/ CONTAINMENT

Geosynthetic placed between an existing crack pavement and an asphalt overlay to minimize the reflection cracking

or delay the propagation of cracks

Geosynthetics (geomembrane or geosynthetic clay liners) canact as relatively impermeable barrier to impede flow of fluids orgases in landfills, waste containment, encapsulation of swellingsoils, asphalt pavement overlays and reflection cracking.


EROSION CONTROLGeosynthetics blanket and mat can control erosion from theearth banks, slopes and silt fences. The mat may be made ofpolymer, jute, coir and wooden fibers.

Geosynthetic placed between subgrade earth bank and rip-

rap for rock protection

Geosynthetic placed at bottom of underwater excavation to

prevent erosionProf. J. N. Mandal, Department of Civil Engineering, IIT Bombay

SCREENWhen the flowing fluid (water, wind) carries particles insuspension, geosynthetic stops the fine particles and allowfluid to pass through. Although the accumulated particlesincrease fluid pressure, screen can withstand the pressure.

Silt fence can be placed to block the water current silt and/ or wind blow sand to stabilize dunes


Vertical silt placed in water to prevent the suspended particles from polluting the downstream water


It can be used as daily cover on the working surface ofmunicipal solid waste landfills to protect it from birds,animals and winds.

Cylindrical shaped double layer geosynthetics called asgeotextile tube filled with hydraulic fill can be used forshoreline protection or to dewater the sludge for waterpurification.

Geosynthetics have several other applications:


MULTIPLE FUNCTIONS OF GEOSYNTHETICS

Reinforced soil walls and steep slopes: The primaryfunction is reinforcement and secondary function is drainage.

Embankments: The primary function is separation andsecondary functions are filtration, drainage and reinforcement.

Railroads: The primary functions are separation andfiltration.

Unpaved roads: The primary function is separation andsecondary functions are filtration, drainage and reinforcement.

Paved roads: The primary function is separation andsecondary functions are filtration, drainage and reinforcement.


Repaving: The primary function is water proofing andsecondary function is reinforcement.

Drainage: The primary function is filtration and secondaryfunctions are separation and drainage.

Hydraulic construction: The primary function is filtrationand secondary function is separation.

Sports fields: The primary function is separation andfiltration.

Tunnels: The primary functions are drainage and protection.

Geomembrane containment: The primary function isprotection and secondary functions are drainage andreinforcement.


DESIGN OF GEOSYNTHETIC

Evaluate the geotechnical properties by soil exploration

Evaluate the properties of geosynthetic materials (i.e.physical, mechanical, hydraulic and environmental etc.)

Determination of geosynthetic functions such as separation,reinforcement, drainage, filtration, protection, containment anderosion control

Try trial design and compare with various alternativemethods

Analyze the proper models and evaluate their parametersProf. J. N. Mandal, Department of Civil Engineering, IIT Bombay

Develop most safe and cost effective appropriate design.

Determine the exact required properties of geosyntheticsand their installation techniques.

Look at the availability of geosynthetics or modify thedesign if required.

Monitor the construction site.


Civil engineers have to face lot of challenges to get theengineering solutions for any project:

Maximum use of local materials and manpower to reducecost and time

Tight time schedules

Various site constraints like space, alignments, social andpolitical problems

Long term performance and higher cost benefit ratio over alarger period of time

Least maintenance cost, and

Least environmental impactProf. J. N. Mandal, Department of Civil Engineering, IIT Bombay

Geosynthetics type and functions

Functions

Type of Geosynthetics

Separation Reinforcement Filtration Drainage Containment

Geotextile

Geogrid

Geonet

Geomembrane

Geosynthetic clay liner

Geopipe

Geofoam

Geocomposite


Applications and functions of geotextile

XGeomembrane containments

XXTunnels

XRetaining walls

XVertical drains

XEmbankments

XXSports fields

XDrainage

XHydraulic

construction

XXRailroads

XRepairing

XUnpaved roads

ProtectionReinforcementDrainageFiltrationSeparationGeotextile functions/ Areas

of application

secondary functionX primary functionProf. J. N. Mandal, Department of Civil Engineering, IIT Bombay

ApplicationsGeosynthetic parameters

Unpaved roads

Rail road

Hydraulic construction

Drainage

Sports field

Embankment

Retaining wall

Tunnel Geomembrane

containment

Puncture resistance (N)

X X X X X X X

Tensile elongation (%)

X X X X X X X

Drop test X X X

Effective opening size (mm)

X X X X X X

Thickness (mm) X X X X X X X X X

Permeability in the plane, Kh (cm/sec)

X X X X X X

Permeability normal to the

plane, Kv (cm/sec)

X X X X X X X

Tear resistance (N) X

Tensile strength (kN/m)

X

Burst pressure resistance (kN/m2)

X

Design parameters and applications of Geosynthetics


Geosynthetics

(g/ m2)

90 110 130 140 180 200 235 280 350 400 500 600 700

800

Road construction

Railroads x x

River bank protection

x x x x

Costal protection

x x

Drainage x x x x

Tunnel construction

x X x x x x x x

Geomembrane protection

x X x x

Retaining walls x X x

THE CORRECT CHOICE OF GEOSYNTHETICS

Generally, the amount of geosynthetics selected depends onthe applied load and soil conditions for various projects.


* Separation, Filtration, drainage reinforcement, protection, sealing

** Soil: grain size distribution, shear strength, permeability, water: Rate of flow, flow conditions

Stress: Static, dynamic

*** Mechanical: Puncture resistance Burst-strength, tear-resistance, tensile strength

Hydraulic: Kv = permeability,

Dw = effective opening width.

Design chart for geotextile

Project analysis

Use of geotextile

Determination of geotextile functions *

Determination of required safety factor

Determination of onsite parameters **

Calculation of minimum required values

Determination of actual geotextile minimum values ***

Calculation of actual safety factor

Comparison of safety factors factual, required

Yes/ No


Please let us hear from you

Any question?


Prof. J. N. Mandal

Department of civil engineering, IIT Bombay, Powai , Mumbai 400076, India. Tel.022-25767328email: [email protected]


GEOSYNTHETICS ENGINEERING: IN THEORY AND PRACTICE · ** Soil: grain size distribution, shear...

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