jpgiroud geosynthetics in roads jakarta 2006 handout.pdf

i

Indonesian Chapter of the International Geosynthetics Society

Road pavements in Indonesia

Seminar held in Jakarta on 6 April 2006

Functions of Geosynthetics in

Road Applications

by

J.P. Giroud Consulting Engineer

JP GIROUD, INC. Chairman Emeritus of GeoSyntec Consultants

Past President of the International Geosynthetics Society

Presentation by Michael Dobie on the next page,

followed by

biographical note and copies of all slides,

Functions of Geosynthetics in Road Applications Jakarta By J.P. GIROUD 2006.04.06

Indonesian Chapter International Geosynthetics Society

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PRESENTATION By Michael Dobie The Indonesian Chapter of IGS (INA-IGS) was formed in 1992, and a two day Inaugural Symposium was held in November 1992, with Keynote Lectures from Kerry Rowe, Bengt Broms and Masami Fukuoka, together with a wide range of papers submitted by authors from Indonesia and overseas. Since that time, few activities have been organised, and the 1997 Asian financial crisis plunged the Indonesian economy, especially construction, into the doldrums. However the situation has been changing and improving in Indonesia in recent years, so in late 2004, actions were taken to reactivate the INA-IGS Chapter, starting with the formation of a new committee and secretariat. A new Chairman was appointed, Prof Chaidir Makarim, and a Secretariat was established at the Universitas Bina Nusantara (BINUS), organised by the head of the Civil Engineering Department, Amelia Makmur. The first event to be organised was a one-day seminar held on 14th February 2005 on the subject Applications of Geosynthetics with Reference to Indonesian Soil Conditions. In April 2006, an opportunity arose to organise another seminar. At this time, Dr J. P. Giroud was making a tour of the Far East to deliver the 2005/6 Mercer Lecture, and had kindly agreed to include Indonesia in his itinerary. The INA-IGS Committee considered that this was a very good opportunity to arrange another one-day seminar, and this time proposed the subject Road construction in Indonesia with special reference to the role of geosynthetics, being highly relevant to current infrastructure plans in Indonesia. Dr. Giroud was asked if he would contribute a presentation outlining the principal applications of geosynthetics in road pavement construction, and we were delighted when he accepted the challenge to create a special presentation on this subject. The seminar was duly organised and held on 6th April 2006 at the JW Marriott Hotel in Jakarta. Indonesia has many thousands of kilometers of road, ranging from major highways, to main distributors and local roads, as well as unsurfaced roads, for example in plantations. National development plans will result in many more thousands of kilometers being constructed. Loadings on this road system are heavy, both in terms of actual axle loads, and the number of vehicles using the roads. These loadings, combined with difficult subgrade conditions and heavy rainfall, can cause severe damage to the road surfacing. This damage results in poor ride quality so that speeds are drastically reduced and the only solution is major repair or possibly reconstruction. In the first half of the seminar, presentations outlined the current and future situation with regards to roads in Indonesia, including a summary of subgrade soils and the problems they pose for road construction, information on axle loadings and current design methods used, especially over poor subgrades. After the scene had been set, Dr. Giroud presented his paper which outlined the various applications and functions of geosynthetic materials in road pavement construction. These applications are generally applied to either the sub-base or upper part of the subgrade, and include separation, filtration, reinforcement, drainage and creation of barriers. These applications were then illustrated using case studies from Indonesia, presented by a number of speakers. The seminar was concluded with an open forum, where members of the audience were given the opportunity to ask questions about the content of the presentations and seek opinions from the assembled speakers. Dr. Giroud has prepared a comprehensive handout that goes beyond what he presented in Jakarta, with more than 50 additional slides, all included in this document.

A handout from the 2005/6 Mercer Lecture Contribution of Geosynthetics to the Geotechnical Aspects of Waste Containment by Dr. J. P. Giroud is also available.



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Dr. J.P. Giroud Dr. Giroud, a pioneer in the field of geosynthetics since 1970, is recognized throughout the world as a geosynthetics leading expert. A former professor of geotechnical engineering, he is a consulting engineer under JP GIROUD, INC., and chairman emeritus and founder of GeoSyntec Consultants. Dr. Giroud is past president of the International Geosynthetics Society (the IGS), chairman of the editorial board of Geosynthetics International, and was Chairman of the Editorial Board of Geotextiles and Geomembranes (1984-1994). Dr. Giroud was chairman of the 2nd International Conference on Geotextiles (1982) and the International Conference on Geomembranes (1984). He served two terms as chairman of the Technical Committee on Geosynthetics of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE). Dr. Giroud coined the terms geotextile and geomembrane in 1977, thus starting the geo-terminology used in geosynthetics engineering. He has authored over 350 publications, including a monumental Geosynthetics Bibliography (1721 pages, more than 10,000 references); and he recently wrote the chapter on filter criteria in the prestigious book commemorating the 75th anniversary of Karl Terzaghis book Erdbaumechanik. Dr. Giroud has developed many of the design methods used in geosynthetics engineering. For example, he developed methods for the evaluation of leakage through liners, for the design of drainage layers (including leachate collection layers and leakage detection layers), for soil cover stability, for the reinforcement of liners and soil layers overlying voids, for the resistance of geomembranes exposed to wind uplift, for the design of unpaved roads, and for the design of geotextile and granular filters. Also, he played a key role in the development of landfill construction quality assurance (1983-1984). Dr. Giroud has extensive field experience and has originated a number of geosynthetics applications such as: first nonwoven geotextile filter (1970), first geotextile filter in a dam (1970), first geotextile cushion for geomembrane (1971), first double liner with two geomembranes (1974), first entirely geosynthetic double liner system with two geomembranes and a geonet leakage detection system (1981). He has been instrumental in the development of the technique of exposed geomembrane landfill covers (1995-1998). Dr. Giroud has received awards from the French Society of Engineers and Scientists, the Industrial Fabrics Association International, and the IGS (in 1994 for liner leakage prediction and in 2004 for filter design). In 1994, the IGS named its highest award The Giroud Lecture, in recognition of the invaluable contributions of Dr. J.P. Giroud to the technical advancement of the geosynthetics discipline. In 2002, Dr. Giroud became Honorary Member of the IGS with the citation Dr. Giroud is truly the father of the International Geosynthetics Society and the geosynthetics industry. In 2005, Dr. Giroud has been awarded the status of hero of the Geo-Institute of the American Society of Civil Engineers (ASCE). It was the first time this new award was granted. Dr. Giroud has delivered keynote lectures at numerous international conferences. In 2005, he presented the prestigious Vienna Terzaghi Lecture, and, in 2005-2006, the prestigious Mercer Lecture series. Dr. Giroud can be contacted at [email protected]



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ABSTRACT Functions of Geosynthetics in Road Applications by J.P. Giroud The main functions of geosynthetics are presented and discussed, and the geosynthetics able to perform the various functions are identified. Then, a simple relationship between the properties and functions of geosynthetics is proposed. However, in most applications geosynthetics perform several functions. Therefore, to understand how geosynthetics perform, applications must be reviewed and the functions performed by the geosynthetics in each of the reviewed applications should be identified. Accordingly, applications of geosynthetics in roads are reviewed. The reviewed applications include: the use of high-strength geosynthetics (geotextiles and geogrids) in road embankments constructed on soft soils; the use of geosynthetics to bridge soil cavities under road embankments; innovative solutions such as the use of lightweight geosynthetics (geofoam) and geogrid mattresses in highway embankments; the design and performance of unpaved roads and unpaved areas with geosynthetics acting as separators and reinforcement, including a detailed discussion of the mechanisms through which a geosynthetic improves the performance of unpaved roads (load distribution, lateral restraint, tensioned membrane effect, and subgrade confinement); the use of innovative solutions such as geocells in unpaved roads and areas; the use and functions of geosynthetics in paved roads and asphalt overlays; the use of geocomposites and prefabricated edge drains for highway drainage, with a discussion of the performance of geotextile filters; the use of geomembranes along highways to protect aquifers from pollution by various contaminants spilled on road pavements; the use of geomembranes to prevent intrusion of groundwater in underground roads; the use of geomembranes for moisture content control in the case of expansive soils, thereby increasing the road service life; and the use of geomembranes to construct road bases using compacted fine-grained soil (membrane encapsulated soil layers). Numerous photographs present actual uses of geosynthetics in the field, and explanations are provided for the beneficial effects of geosynthetics. At the same time, limitations of the uses of geosynthetics are presented and recommendations are made for the safe use of geosynthetics in road applications. References cited in the presentation: Bonaparte, R., Holtz, R.D., and Giroud, J.P., 1985, Soil Reinforcement Design Using Geotextiles and

Geogrids, ASTM Symposium, Geotextile Testing and the Design Engineer, ASTM STP 952, Los Angeles, CA, USA, June 1985, pp. 69-116.

Giroud, J.P., Bonaparte, R., Beech, J.F., and Gross, B.A., 1990, Design of Soil Layer-Geosynthetic Systems Overlying Voids, Geotextiles and Geomembranes, Vol. 9, No. 1, Elsevier, London, England, pp. 11-50.

Giroud, J.P., and Han, J., 2004, Design Method for Geogrid-Reinforced Unpaved Roads. I Development of Design Method, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 130, No. 8, August 2004, pp. 775-786.

Giroud, J.P., and Han, J., 2004, Design Method for Geogrid-Reinforced Unpaved Roads. II Calibration and Applications, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 130, No. 8, August 2004, pp. 787-797.

Functions of Geosynthetics in Road ApplicationsBy J.P. GIROUD

Jakarta2006.04.06


1

J.P. GIROUDROAD PAVEMENTS

IN INDONESIA

Indonesian Chapter

International Geosynthetics Society

J.P. GIROUD

FUNCTIONS OF GEOSYNTHETICS IN ROAD APPLICATIONS

J.P. GIROUD

J.P. GIROUD

Today, geosynthetics are part of the road construction landscape.

This is because geosynthetics are used

in many road applications where they perform

a variety of functions.

Lets start with the four classical functions:

TRANSMISSION FILTRATION SEPARATION REINFORCEMENT

These functions were first identified for geotextiles.

TRANSMISSION

The geosynthetic conveys water

within its plane.

Types of geosynthetics: Needle-punched nonwoven geotextiles , geonets, geomats

Main relevant properties: Hydraulic transmissivity (= thickness permeability)


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THICK NEEDLE-PUNCHED NONWOVEN GEOTEXTILE GEONETS

Geonets can convey water within their channels.

GEONET DRAIN

GEOTEXTILE FILTER

SOIL COVER

Example of geonet as leachate collection layer

in a landfill

FILTRATION

The geosynthetic allows water to pass

while retaining the sol.

Example of geotextile filter between gravel drain and soil


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FILTRATION



Types of geosynthetics: geotextiles, but

some geotextiles are adequate, some are not.

a needle-punched nonwoven geotextile is generally adequate,

a slit-film woven geotextile

is not.

For filtration,

a monofilament woven geotextile is often adequate,

FILTRATION



Types of geosynthetics: some geotextiles

Main relevant properties:permeability, retention

TRANSMISSION & FILTRATION

Types of material for the core: geonet, geomat, cuspated sheet

A geotextile filter is associated with

a transmissive core to form a geocomposite.

GEOCOMPOSITE

Geotextile filter

Geonetdrain core

The drain core of a geocomposite can also be:

GEOMAT CUSPATED SHEET


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ILLUSTRATION OF FILTRATION AND TRANSMISSION

There are also very thick geocompositesmade especially for road edge drains.

SEPARATION

The geosynthetic separates two materials that tend to

mix when they are squeezed together by applied loads.

WITH SEPARATION

SEPARATION



Types of geosynthetics: geotextiles

Needle-punched nonwoven geotextile used as separator


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SEPARATION



Types of geosynthetics: geotextiles

Main relevant properties:permeability, retention,

resistance to concentrated stresses

To resist concentrated stresses, the geotextile must have

high strength and elongation.

REINFORCEMENT The geosynthetic

carries tensile loads that the soil is

unable to carry.



unable to carry.

Types of geosynthetics:high-strength geotextiles, geogrids

HIGH-STRENGTH WOVEN GEOTEXTILE Multi-layer reinforced soil wall during construction


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Light concrete panels protect the geotextile from deterioration caused by exposure to sunlight.

GEOGRIDS

RETAINING WALLLight concrete blocks

used as facing

Geogrid reinforcement

PROTECTION AGAINST ROCKFALL

Geogrid-reinforced structure


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LANDSLIDE REPAIR

Geogrid-reinforced steep slope



unable to carry.

Types of geosynthetics:high-strength geotextiles, geogrids

Main relevant properties:tensile strength and modulus,

interface shear strength

INTERFACE SHEAR STRENGTH

Interface adhesion Interface friction Interlocking

Geogrid

Load

INTERLOCKINGInterlocking exists only with geogrids,and only if there is

adequate relationshipbetween the

geogrid opening size and the soil particle size.

EXAMPLE OF GOOD INTERLOCKING


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EXAMPLE OF GOOD INTERLOCKING

EXAMPLE OF POOR INTERLOCKING

PARAMETERS OF INTERLOCKING

Geogrid aperture size relative to aggregate size.

Shape and stiffness of transverse ribs.

Strength of junction between perpendicular ribs.

The reinforcement function of a geosynthetic is more effective

if there is less relative displacement between the geosynthetic and the soil to be reinforced.

If there is good interlocking between a geogrid and soil,

it is believed that the relative displacement required to mobilize interlocking

is less than the relative displacement required to mobilize interface friction

(which is the other interface mechanism).

SEPARATION & REINFORCEMENTA geotextile

is associated

with a geogrid.

Properties & FUNCTIONS

Thickness

Permeability

Retention

Strength

Interface

TRANSMISSION

FILTRATION

SEPARATION

REINFORCEMENT

SIMPLE RELATIONSHIP BETWEEN


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The functions reviewed so far do not include

the fluid barrier function performed by geomembranes.

(This function will be discussed at the end.)

After this review of functions,lets talk about applications

of geosynthetics.

In a given application, a given geosynthetic will often perform

several functions.

Therefore, applications should be reviewed, and the functions identified.

APPLICATIONS OF

GEOSYNTHETICS IN ROADSTHREE CATEGORIES:

Applications in road foundation

Applications in road structure

Applications in controlling water

APPLICATIONS OF





APPLICATIONS OF GEOSYNTHETICS

INROAD FOUNDATION

Embankment on soft soil

Cavity bridging

EMBANKMENT ON SOFT SOIL

The geotextile performs two functions:

SEPARATION

REINFORCEMENT


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Corduroy logs

Earth Fill 2

1 > 1m

Peat Soil Cu < 8 kPa> 5m

Rock GX geogrid 35/35 TS70 geotextileGEOGRID GEOTEXTILE

Here, the geotextile acts as a separatorbetween the soil

that could pass through the openings of the geogridand the logs.

RAPP Airstrip Project in IndonesiaHere a geotextile will be used as a separator

between the embankment soil and a very coarse material, the logs.

REINFORCEMENT

SEPARATOR

Road Construction on Peat Soil in Indonesia

Rock PEC 50 (50 kN/m)

Earth Fill Sandy gravel

2

1 1m

7m

Peat Soil Cu < 8 kPa 9mGEOTEXTILE

Here, the geotextile may act as a separator between the earth fill and the peat.

However, it certainly acts as reinforcement.

This is one of the most typical uses of geotextiles.


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The reinforcement function is often needed

as soon as the beginning of construction.

CONSTRUCTION ON SOFT SOIL


The geosynthetic provides support.This is a first illustration of

the tensioned membrane effect

CONSTRUCTION ON SOFT SOILHere, too,

the geotextile provides support.



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In some other cases, the field situation is better

and reinforcement is only needed

for the long term.


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Another way of using geogrids at the base of an embankment

GEOGRID MATTRESS FILLED WITH SOIL

GEOGRID MATTRESSGeogrids

placed vertically and assembled

The geogrids are positioned vertically and tensioned. Steel bodkins are inserted to form joints.

STEEL BODKIN JOINTS Geogrid cells ready for backfilling


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BACKFILLING EQUIPMENT SUPPORTED BY BACKFILLED CELLS

DISCUSSION OF THE

REINFORCEMENT FUNCTIONIN

EMBANKMENTS ON SOFT SOIL

Overview of completed track formation wall open to traffic.EMBANKMENT FAILURE THE THREE FAILURE MECHANISMS

LATERAL SLIDING

SLIP SURFACE FAILURE

BEARING CAPACITY FAILURE

Bonaparte, Holtz, and Giroud (1987)

Tt

t

Lateral Sliding

The geosynthetic restrains the lateral movement of the embankment.

Slip Surface Failure

T = ?

Reinforcement


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D = ?

Reinforcement

H = ?

V = ?

Bearing Capacity Failure Slip surface failure and bearing capacity failure

can be avoided by using lightweight embankment.

GEOFOAM

In addition to improving stability and bearing capacity, lightweight fill (using geofoam)

significantly decreases settlement. Indeed, settlement is due to

the embankment weight.

It is important to recognize that geotextiles and geogrids

have no impact on global settlementbecause they perform

the separation and reinforcement functions that have no impact on global settlement.

Geosynthetics (other than geofoam) have no impact on global settlement,but it is important to recognize that they may have a significant impact

on differential settlementwhen the foundation soil is not uniform.

In other words, the geosynthetics (other than geofoam)

have no impacton the magnitude of settlement,

but they may have a significant impacton the distribution of settlement.

Geosynthetics may have a significant impact on differential settlement

when the foundation soil is not uniform.

This is the case in particular when geosynthetics stiffen the base of the embankment, which makes the distribution of settlement more uniform.

Other mechanisms will be discussed later.

Examples: geogrid cells or multiple layers of geogrids

at the base of embankments.

EXAMPLE OF DIFFERENTIAL SETTLEMENT


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INROAD FOUNDATION

Embankment on soft soil

Cavity bridging

INDONESIA

TUNISIA FRANCE

One or several layers of high-strength geosynthetic can be used to bridge a cavity.

The geosynthetic performs THE REINFORCEMENT FUNCTION

CAVITY BRIDGING


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Bending of the soil, hence arching

Stretching of the geosynthetic, hence tension

Cavit

ARCHING

TENSIONED MEMBRANE

Thanks to arching, only part of the overburden load is applied to the geosynthetic.

DESIGN METHOD ACCOUNTING

FOR BOTH ARCHING IN SOIL

AND TENSIONED MEMBRANE

IN GEOSYNTHETIC

(Giroud et al. 1990)

However, in road structures,

functions are more complex.

So far, the functions were easy to identify.

APPLICATIONS OF






IN ROAD STRUCTURE

Unpaved roads

Paved roads

Asphalt overlay


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GEOSYNTHETICS IN

UNPAVED ROADS

UNPAVED ROAD WITHOUT GEOSYNTHETIC

UNPAVED ROAD WITH GEOTEXTILE

UNPAVED ROADWITH

GEOGRID

UNPAVED ROADS

The geosynthetic performs two functions:

SEPARATION

REINFORCEMENT


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There is obviously a beneficial effect of separation

when geotextiles are used in unpaved roads.

SEPARATION WITH GEOTEXTILE

Section without geotextile: dark color

Section with geotextile: light color

Photo taken after intensive traffic

MECHANISMS OF DETERIORATION

Also, there is obviously a beneficial effect of reinforcement, with both geotextiles and geogrids.

But, how does it work?

There is obviously a beneficial effect of separation

when geotextiles are used in unpaved roads.

REINFORCEMENT FUNCTIONIN

UNPAVED ROADS

Load distribution Tensioned membrane Subgrade confinement

LOAD DISTRIBUTIONIt is known from the theory of elasticity that,

in a two-layer system, the load distribution on the lower layer

depends on the modulus of the upper layer.


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TWO-LAYER SYSTEM

E1 > E2

E2

Stress

Stress in uniform soil

DISTRIBUTION OF NORMAL

STRESS

LOAD DISTRIBUTIONIt is known from the theory of elasticity that,

in a two-layer system, the distribution of load on the lower layer

depends on the modulus of the upper layer.

It is also known from the theory of elasticity that there are tensile stressesat the bottom of the upper layer,

which limits the load distribution effectiveness.

Tensile stresses at the bottom of the upper layer

With its high modulus, the upper layer is acting as a beam, which explains the tensile stresses.

LOAD DISTRIBUTION(continued)

Therefore, the load distribution effectiveness of the upper layer can be increased

by adding tensile stiffnessat the bottom of the upper layer.

Hence the use of reinforcementat the bottom of the upper layer, which provides lateral restraint.

ILLUSTRATION OF LOAD DISTRIBUTION


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Gravel layer

Soft clay

Thinner gravel layer with reinforcement results in same stress as thicker gravel layer without reinforcement .

LOAD DISTRIBUTION

Load distribution can also be achieved

by geocells.

GEOCELLS

GEOCELLS BEING

DEPLOYED

GEOCELLS FILLED WITH

AGGREGATE

GEOCELL MATTRESS

FILLED WITH

AGGREGATEAND

SUPPORTINGLOADS


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UNPAVED ROAD TO BE CONSTRUCTED

USING GEOCELLS

PLACEMENT OF GEOTEXTILE

PLACEMENT OF GEOCELL PLACEMENT OF BASE MATERIAL

GEOCELL

UNPAVED ROAD COMPLETED REINFORCEMENT FUNCTION

INUNPAVED ROADS



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TENSIONED MEMBRANE EFFECT

Due to the traffic loads, the geotextile is deformed and is, therefore, under tension.

Under the wheels, due to rutting,the geotextile has a concave shape.


The geotextile tension on each side of the concave shape is shown in green.

The resultants of these tensions are shown in red. These resultants contribute to wheel support.

The tensioned membrane effect requires rutting.

Ruts in full-scale test

RUTTING IN THE FIELD

LIMITATIONS OF THE


The tensioned membrane effect is relatively small.

The tensioned membrane effect works only with channelized traffic.

Typically, ruts are periodically backfilled.


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If the traffic continues to be channelized, the tensioned membrane effect

continues to contribute to wheel support.

If the traffic is no longer channelized, the tensioned membrane effect

does not contribute to wheel support.

Traffic is not channelizedin the case of unpaved areas (area stabilization, log yards,

etc.).

AREA STABILIZATION

LOG YARDREINFORCEMENT FUNCTION

INUNPAVED ROADS



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Geotextile confining the subgrade soil

Test at WES

SUBGRADE CONFINEMENTThanks to the presence of the geosynthetic,

the deformations of the soil are limited.

As a result, the soil can be loaded near its ultimate bearing capacity,

and not only near its elastic limit.

d

Pressure p

d

p

uc( ) + 2 uc ULTIMATE BEARING CAPACITY

ELASTIC LIMIT

Without subgrade confinement, a load equal to the ultimate bearing capacity

would cause immediate failure. In other words, an unpaved road

with no subgrade confinement by geosynthetic would fail at one axle pass

if the load at the subgrade soil level is equal to the ultimate bearing capacity.

Therefore, unpaved roads without geosynthetic must be designed to avoid loads

equal to the ultimate bearing capacity. As a result, they must be designedfor loads equal to the elastic limit.

Another approach to subgrade confinement

is to consider that subgrade confinement

is similar to tensioned membrane effect.

This results in a slight increase in bearing capacity of the subgrade soil,

which allows the unpaved road to be safely designed

with the ultimate bearing capacity.


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d

Pressure p

d

p

uc( ) + 2 uc WITHOUT

SUBGRADE CONFINEMENT

WITH SUBGRADE CONFINEMENT


Elastic limit: = up cUltimate bearing capacity:

(normal stress) ( )= + 2 up c

is applicable to the case of normal stress. This is approximately the case of

geotextile-reinforced unpaved roads.

( )= + 2 up cThe usual equation for ultimate bearing capacity,

= + 3 12 u

p c

In the case of geogrid-reinforced unpaved roads, the stresses at the base-subgrade interface

are inclined (due to lateral restraint); as a result, the bearing capacity is slightly increased.


Elastic limit: = up cUltimate bearing capacity:

(normal stress) ( )= + 2 up c

= + 3 12 u

p cUltimate bearing capacity:

(inclined stress)


Elastic limit: = 3.14 up cUltimate bearing capacity:

(normal stress) = 5.14 up c

= 5.71 up cUltimate bearing capacity:(inclined stress) +82%

+64%

DEFORMATION ASSOCIATED WITH THE VARIOUS

REINFORCEMENT MECHANISMS

Much less deformation (i.e. less rutting)is required to mobilize

lateral restraint and load distribution than the tensioned membrane effect.

Consequence : lateral restraint will play an important role in paved roads.


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GENERAL COMMENT ON ACTION OF REINFORCEMENT

IN ROAD STRUCTURE

The mode of action of reinforcement in a road structure is complex because the working condition

for the reinforcement is not ideal since the load is vertical

while the reinforcement is horizontal.

This leads to a variety of modes of action such as lateral restraint, load distribution,

tensioned membrane, subgrade confinement, etc.

IMPORTANT BENEFITGeosynthetic reinforcement in road applications (i.e. under embankments or in road structures)

improves structure behavior by distributing stresses and bridging weak areas

in the case on non-uniform soils. This benefit is difficult to quantify,

but it is real as it results from a combination of mechanisms

such as cavity bridging, load distribution, tensioned membrane, subgrade confinement, etc.

This is an important benefit because non-uniform soils are frequent and unpredictable.

One aspect of this important benefit is the decrease of differential settlement

in the case of non-uniform soils, as discussed earlier

for embankments on soft soils.

IMPORTANT BENEFITIN THE CASE OF NON-UNIFORM SOILS

The Giroud Han Design Method

There is a design method for unpaved roads that takes into account

the mechanisms described above (except the tensioned membrane effect).

Giroud Han Design Method

Main features of design method Theoretically based;

uses bearing capacity theory and stress distribution

Calibrated using field data and cyclic plate load testing in the laboratory


Input parameters:P = wheel load (kN)r = radius of tire print (m) N = number of axle passes CBRbc = base course CBR (%)CBRsg = subgrade CBR (%)

2

1.52

2

0.3

0.868 (0.661 1.006 ) log1

3.481 0.204 1 1 0.9r

bc hc c sg

sg s

PrJ Nrhh r

CBR s e N f CBRCBR f

+ = +

h = required thickness (m)(on both sides of equation)


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s = maximum rut depth (mm) fs = rut depth factor (= 75mm) J = geogrid aperture stability modulus (m-N/degree)Nc = bearing capacity factor

For unreinforced pavements, Nc = 3.14For geotextile-reinforced pavements, Nc = 5.14For geogrid-reinforced pavements, Nc = 5.71

fc = factor relating CBR of subgrade to equivalent cu value (fc = 30 i.e. cu = 30 x CBR with cu in kPa)


2

1.52

2

0.3

0.868 (0.661 1.006 ) log1

3.481 0.204 1 1 0.9r

bc hc c sg

sg s

PrJ Nrhh r

CBR s e N f CBRCBR f

+ = +


IN ROAD STRUCTURE

Unpaved roads

Paved roads

Asphalt overlay

Surfacing layers

Subgrade

Granular baseSub-base

PAVED ROADIDEAL CROSS SECTION

Excellent lateral drainage

Surfacing layers

Subgrade

Sub-baseGranular base

In many cases, the road structure is buried and lateral drainage is difficult.

PAVED ROADS

The geotextile performs two functions:

SEPARATION

REINFORCEMENT

From the viewpoint of the reinforcement function,

a major differencebetween paved roads and unpaved roads

is the magnitude of deformation, because acceptable rutting is much less in paved roads than in unpaved roads.


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The only mechanism of reinforcement that is effective in paved roads

is the load distribution improvement that results from lateral restraint

because this mechanism works with small deformation.

Also, lateral restraint has a long-term beneficial effect

by reducing aggregate base deterioration.

ROAD BASE

Geogrid

Importance of interlocking

to ensure lateral restraint

USE OF GEOGRID FOR ROAD WIDENINGAPPLICATIONS OF GEOSYNTHETICS

IN ROAD STRUCTURE

Unpaved roads

Paved roads

Asphalt overlay


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Asphalt impregnated geotextile retards crack propagation.

This geotextile function is quite different from the

functions discussed so far.

GEOTEXTILE FUNCTION IN ASPHALT OVERLAY

The geotextile impregnated with bitumenis impermeable and acts as a water barrier, preventing precipitation water from percolating into the road base and subgrade.

The geotextile impregnated with bitumenhas a visco-elastic behavior and acts as a crack barrier, slowing down crack propagation.

BLOCK CRACKING

In the case of block cracking, use of strips of geotextile

impregnated with bitumen. Strips of geotextile impregnated with bitumen

ALLIGATOR CRACKING

In the case of alligator cracking, use of full-width geotextile.

ASPHALT OVERLAY


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This is important because any extra thickness of the geotextile (due to a crease or a flattened wrinkle) may initiate a crackin the asphalt overlay.

It is important to use a system that places the geotextile without pleats and wrinkles.

Geotextile placed without wrinkles

APPLICATIONS OF






IN WATER CONTROL

Drainage

Groundwater control

Moisture control

DRAINAGE IN ROADS

Edge drains

Drainage in pavement structure

EDGE DRAINSIt is important to understand

the filtration function. Intimate contact

between the filter and soil is essential.


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IMPORTANCE OF INTIMATE CONTACT BETWEEN GEOTEXTILE FILTER AND SOIL

BAD GOOD

LESSON LEARNED FROM THE GOOD CASE AND THE BAD CASE

In the good case, small aggregate is used, and this aggregate is slightly compacted. As a result, the geotextile filter is pushed against the soil and there is intimate contactbetween the geotextile filter and the soil.

In the bad case, coarse stones are used, and as a result the geotextile filter is not in intimate contact with the soil. Therefore, when water flows from the soil toward the drain, particles accumulate in the space between the soil and the geotextile. This is one of the main causes of clogging of geotextile filters.


the filtration function. Intimate contact

between the filter and soil is essential.

Therefore, a geocomposite used as edge drain

must be in intimate contact with the soil.

approx.0.5 m

TYPICAL GEOCOMPOSITE USED AS EDGE

DRAIN

The relatively rigid structure

makes it difficult to achieve

intimate contact with the soil.

Typical thickness 30 mm


the filtration function.

This leads to backfilling with sand.

Intimate contact between the geocomposite and soil

is essential.


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Sand Backfill

Geocomposite drain

Aggregate base

Subbase/Subgrade

25 mm

100 mm

ShoulderAC/PCC pavement

BACKFILLING WITH SAND BETWEEN RIGID GEOCOMPOSITE EDGE DRAIN

AND SOILTO ENSURE INTIMATE CONTACT

Intimate contact between filter and soil

is also important in the case of

granular drains.

Filling trench with small

aggregate to ensure intimate contact.

Compacting aggregate to ensure intimate contact.

(light compaction)

DRAINAGE IN ROADS

Edge drains

Drainage in pavement structure

Maine Department of Transportation Maine Department of Transportation Frankfort to Winterport HighwayFrankfort to Winterport Highway


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Drainage Test Sections Drainage Test Sections

In this application, the function is

TRANSMISSION, and the geosynthetic is

a geocomposite.

Average installation time: 4 min. for 4m x 60m panel.

DEPLOYING THE GEOCOMPOSITE Drainage Test Sections

Base course aggregate placed on top of geocomposite

CONNECTION WITH COLLECTOR PIPE


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CONNECTION WITH COLLECTOR PIPETexas Department of Transportation

Southwest Parkway Street Reconstruction Project

Drainage Test Sections

GEOCOMPOSITE UNDERNEATH HOT-MIX ASPHALT

GEOCOMPOSITE UNDERNEATHHOT-MIX ASPHALT


IN WATER CONTROL

Drainage

Groundwater control

Moisture control

GROUNDWATER CONTROL Highway under groundwater table Protection of aquifer


WATER BARRIER, and the geosynthetic is

a geomembrane.


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GROUNDWATER CONTROL

Highway under groundwater table

Protection of aquifer

Below-ground highway in Ireland

Geomembrane bathtub against groundwater BITUMINOUS GEOMEMBRANE

Low-permeability soil on top of geomembrane

CROSS SECTION

to form a composite liner with the geomembrane

1 m clay

weight of 3.3 m of soil (including the clay)to counteract uplift by ground water pressure


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GROUNDWATER CONTROL Highway under groundwater table Protection of aquifer


WATER BARRIER, and the geosynthetic is

a geomembrane.

A significant amount of groundwater pollution is caused by spillage of various contaminants, including gasoline. These contaminants are

collected in swales lined with a geomembrane.

Placement of bituminous geomembrane by hand

Placement of bituminous geomembrane by equipment

1995 Switzerland1995 Switzerland

To protect an important aquifer, the entire highway excavation is lined with a geomembrane.


IN WATER CONTROL

Drainage

Groundwater control

Moisture control


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MOISTURE CONTROL Use of geomembranes along highways

to control the moisture contentof expansive soils

MESLs(membrane encapsulated soil layers)

USE OF GEOMEMBRANES ALONG HIGHWAYS TO CONTROL THE MOISTURE CONTENT

OF EXPANSIVE SOILS

With expansive subgrade soil, the service life of a road may be 5 years instead of 20 years.

The purpose of the geomembrane is to stabilize the moisture contentof the subgrade soil.

Typically, moisture content fluctuatesdown to a depth of 1.5 to 3.0 m.

VERTICAL GEOMEMBRANE

Flowable backfill (slurry)

Geomembrane

Trench width:0.5 m backhoe0.1 m trencher

Trench depth:1.5 m to 3.0 m typical: 2.5 m

VERTICAL AND HORIZONTAL GEOMEMBRANE

Flowable backfill (slurry)

Geomembrane

MOISTURE CONTROL Use of geomembranes along highways

to control the moisture contentof expansive clays

MESLs(membrane encapsulated soil layers)

COMPACTED SOIL

GEOMEMBRANE

SUBGRADE SOIL

MEMBRANE ENCAPSULATED SOIL LAYER

MESL


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The geomembrane is delivered. The bituminous geomembrane is unrolled.

The soil layer is compacted. The geomembrane is wrapped around the compacted soil layer.

The completed MESL

CONCLUSION


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Properties & FUNCTIONS

Thickness

Permeability

Retention

Strength

Interface

TRANSMISSION

FILTRATION

SEPARATION

REINFORCEMENT

Based on what we have learned, this appears to be a very simplified relationship between properties and functions of geosynthetics.

In reality, more functions are performed and, for a given function, several mechanisms can be considered.

This is particularly true for the reinforcement function. Remember: load distribution, lateral restraint, tensioned membrane, and subgrade confinement.

However, this slide summarizes the spirit of this presentation. For each application, the relevant functions are identified, which leads to the relevant properties, which in turn leads to the selection of the most appropriate geosynthetic.

COMMENTS ON THE PRECEDING SLIDE

Thank you

jpgiroud geosynthetics in roads jakarta 2006 handout.pdf

Documents

indonesia seminar

functions of geosynthetics

road applications jakarta

subject road construction

role of geosynthetics

road system

road surfacing

day seminar