Hafez Geotextile Hafez2009

Geosynthetics

Dr/ M. Hafez

[email protected]

mailto:[email protected]

Geotextile

Geotextiles are made to be adaptable for solving

problems associated with soil and water conservation

work. They can be very effective in improving drainage,

protecting against piping or erosion and providing

reinforcement or separation of fill materials. Proper

design is necessary to ensure adequate function or

service.

Geotextile type is determined by the method used to

combine the filaments or tapes into the planar textile

structure. The vast majority of geotextiles are either

woven or nonwoven.

History of soil reinforcement

Allow overlap ≥

600mm

CONSTRUCTION SEQUENCE OF GEOBAMTILE

Existing soil

INTRODUCTION

Geosynthetics is the term used to describe a

range of generally synthetic products used to

solve geotechnical problems.

The term is generally regarded to encompass

four main products: geotextiles,

geonets/geogrids, geomembranes and

geocomposites.

Introduction

GEOSYNTHETICS

ASTM has defined a geosynthetic as a planar product manufactured from a polymeric material used with soil, rock, earth or other geotechnical-related material as an integral part of a civil engineering project, structure, or system.

Geosynthetics are used for solving problems associated with soil and water conservation work. They can be very effective in improving drainage, protecting against piping or erosion and providing reinforcement or separation of fill materials.

Introduction (cont.)

Most of geosynthetics are made from synthetic polymers such as polypropylene, polyester, polyethylene, polyamide, PVC, etc. These materials are highly resistant to biological and chemical degradation.

Natural fibers such as cotton, jute, and bamboo, could be used as geotextiles and geogrids.

These fibers are used in all fields of civil engineering to increase the safety and life span of structures.

Type of geosynthetics are;

Geotextile - is a permeable geosynthetic made of textile materials.

Geogrids - are primarily used for reinforcement; they are formed by a regular network of tensile elements with apertures of sufficient size to interlock with surrounding fill material.

Geomembranes - are low permeability geosynthetics used as fluid barriers.


These products have a wide range of

applications and are currently used in

many civil and geotechnical

engineering applications including

roads, airfields, railroads,

embankments, reservoirs, canals,

dams, and coastal engineering.

Three products above (geotextiles, geogrids, and

geomembranes) can be combined by two or three

materials to take advantage of the best attributes of each

component.

These products are called geocomposites (e.g., deformed

plastic sheets, steel cables, or steel anchors).


Fig. 5 Classification of geotextiles

Geosynthetics Technology

Billion dollar industry

About 100 civil and environmental

engineering applications

Geosynthetics Market

1970: Less than 1 million m2

1995: 700 million m2, $1.67 billion

Geotextiles: 500 million m2

Geomembranes: 75 million m2

Geonets: 50 million m2

Geogrids: 40 million m2

GCLs: 50 million m2

Geocomposites: 25 million m2

Materials

Polypropylene

Polyethylene

Polyester

Poly vinyl chloride (PVC)

Functions

Reinforcement

Separation

Filtration

Drainage

Containment

Parameters for Geosynthetics

Selection

Application Requirements

Design Method

Required GS properties

Functions

GEOTEXTILE TYPES

Non Woven Material


Fig. 1 Geotextiles

(a) woven

(b) nonwoven

Non-woven geotextile

arrangement of fibers either oriented or randomly patterned in

a sheet

provide planar water flow in addition to stabilization of soil

Woven geotextile

a fabric made of two sets of parallel strands systematically

interlaced (form a thin, flat fabric)

preferred for applications for high strength properties

filtration requirements are less critical and planar flow is not

a consideration

reduce localized shear failure in weak subsoil conditions,

improving construction over soft subsoil and providing access to

remote areas through separation.

Ideally vegetation can form the best erosion control (difficult to establish)

Non-woven geotextile over sub-

grade prior to top course for

Equestrian Area

Non-wovens are specifically

engineered for asphalt overlays as

a fabric interlayer between the old

and new asphalt layers in flexible

pavement systems, extending

roadway life


Fig. 2 Geogrids

(a) Uniaxial

(b) Biaxial


Fig. 3 Geomembranes

(a) Smooth

(b) Textured


Fig. 4 Geocomposites

Geotextiles perform one or more basic functions below;

Reinforcement of weak soils and other materials.

Drainage (in-plane flow).

Filtration (cross-plane flow).

Separation of dissimilar materials.

Functions

FUNCTION OF

GEOSYNTHETICS

Separation

Reinforcement

Drainage

Filter

Energy Absorber

Container

Barrier

REINFORCEMENT

DRAINAGE FILTRATION

SEPARATION

Fig. 6 Function and application of geotextiles

CONTAINER

Geosynthethis containment applications are those in which a textile in the form of a tube, bag or container, is used to encapsulate a construction material, such as soil or sand.

Geotextile sand container (1m3) made of

nonwoven textile

APPLICATIONS

Groundwater

Protection In

Transportation

Infrastructure

Installation of geomembrane with a spreader

bar in a road ditch

For road construction in environmentally sensitive areas require subsoil be sealed and effective construction measures be taken to protect the groundwater in transport infrastructure near to water catchment areas.

Bentofix road barrier system

The classic application of a geotextile as a liquid

barrier is paved road rehabilitation.

Here the nonwoven geotextile is placed on the

existing pavement surface following the application of

an asphalt tack coat.

The geotextile absorbs asphalt to become a

waterproofing membrane minimizing vertical flow of

water into the pavement structure.

Dammed-up Waters

In inland fresh water shipping routes where the water level is an elevation higher than the natural groundwater level, artificial barrier is required to prevent the water ‘draining’ to the groundwater level.

Barrier of a harbour basin with

Bentofix Geosynthetic Clay

Liner

Barrier of a canal with the Bentofix BZ 13-B, for underwater installation

Dyke Construction

Cross section of dyke,

sealed with Bentofix

Geosynthetics Clay

Liner and downstream

root barrier with

Carbofol geomembrane

EXAMPLE APPLICATION Scour stabilization

In rivers, waterways and open sea areas scour can be caused by natural currents or erosion effects due to ship movements, such as natural gradients or drift currents, waves, backflow currents and ship's screw actions.

The stability of waterfront structures, bridge piles and slopes of waterways at narrow passage openings can be endangered by progressive scour development

Scour development at bridge

piles (left), flexible scour

protection at the bottom with

sand containers (right),

schematically drawn

BARRIER

The geosynthetic acts as a relatively impermeable

barrier to liquid (fluids) or gases.

For example, geomembranes, thin film geotextile

composites, geosynthetic clay liners (GCLs) and field-

coated geotextiles are used as fluid barriers to impede

flow of liquid or gas.

For barrier purposes in hydraulic engineering, road

construction and environmental protection, HDPE

geomembranes and geosynthetics clay liners are

gaining use due to importance of a quality seal.

Scour protection with geotextile sand

containers at the bottom of bridge piles

Breakwaters

A series of offshore or shore attached breakwaters, could be used to maintain

and build up the beach in front of the shoreline along the frontage at the Murrough

Revetments

Providing protection against erosion of the

shoreline

Erosion Control / Coastal Protection

Geosynthetic as a Separator

As a separation layer, geotextile are used to prevent

adjacent soil layers or fill materials from intermixing.

Synthetic nonwovens that exhibit an elongation capacity,

are the materials of choice in most applications. The

selection of a suitable product is dependant upon the base

course grain size and the operational loads to be

expected.

The main use of separation nonwovens are in road and

railway construction, hydraulic and landfill engineering and

field construction.

Geotextiles can be used as separators to prevent

fine- grained subgrade soils from being pumped into

permeable, granular road bases and to prevent road

base materials from penetrating into the underlying

soft subgrade.

Separators maintain the design thickness and

roadway integrity.

Separator

Preventing the intermixing of soft foundation soils with granular material .

Separator (cont.)

Fig. 19 Separator

Geotextiles are used as an integral component in reinforced soil structures such as retaining walls, slopes and embankment.

Provide tensile resistance to the soils, thus enhancing its shear characteristic.

Enables embankments to be constructed over very soft foundations.

Reinforcement

Maintaining the stability of soil by carrying tensile load.

Reinforcement (cont.)

Fig. 7 Reinforcement process

They are also used to construct stable slopes at much steeper

angles.

Geotextiles which used for reinforcement are design on ideal

characteristic.

High tensile strength

Low elongation

Low creep.



The three primary applications of soil reinforcement using

geotextiles are;

1) reinforcing the base of embankments constructed on very soft foundation

2) increasing the stability and steepness of slopes,

3) reducing the earth pressures behind retaining walls and abutments.

Other reinforcement and stabilization applications which geotextiles are also be proven to be very effective include roads and railroads, large area stabilization, and natural slope reinforcement.

Slope reinforcement

Embankment

reinforcement


Fig. 8 Type of reinforcement

Properties of reinforcement geotextiles (woven)

Reinforcement embankment on

soft ground

Concept

The design and construction of embankments on soft foundation soils is a very challenging geotechnical problem.

Successful projects require a thorough subsurface investigation, properties determination, and settlement and stability.

If the settlements are too large or instability is likely, then some type of foundation soil improvement is warranted.


soft ground (cont.)

Today, geotextiles reinforcement must also be considered as a feasible treatment alternative.

In some situations, the most economical final design may be some combination of a traditional foundation treatment alternative together with geotextiles reinforcement.

The addition of strength tensile element in the soil embankment contribute to the resisting force and hence the overall stability of the structure.

Increasing the design factor of safety.

Fig. 10 Bearing failure

Fig. 9 Concept


soft ground (cont.)

Fig. 11 Rotational failure

Fig. 12 Lateral spreading


soft ground (cont.)

Design Considerations

As with ordinary embankments on soft soils, the basic design approach for reinforced embankments is to design against failure. The ways in which embankments constructed on soft foundations can fail have been described by Terzaghi et al. (1996).

The three possible modes of failure indicate the types of stability analyses that are required for design.


soft ground (cont.)

Design Considerations

Overall bearing capacity of the embankment must be adequate, and the reinforcement should be strong enough to prevent rotational failures at the edge of the embankment. Lateral spreading failures can be prevented by the development of adequate shearing resistance between the base of the embankment and the reinforcement.


soft ground (cont.)

Fig. 13 Geotextiles used in the reinforcement slope

Reinforcement of steep slope (cont.)

Fig. 14 Geotextiles used in the reinforcement slope

Reinforcement of steep slope (cont.)

to convey fluid within the plane of the fabric. The thicker nonwoven geotextiles have this capacity, while woven and heat bonded nonwoven geotextiles do not.

Geotextiles are used for the drainage or structures which are in contact with soil. Thereby, reducing the hydrostatic pressure on the structures and its sealing system.

They also used as a drainage material for the surface collection of precipitation, the subsurface collection and diversion of groundwater as well as the general collection of fluids and their discharge into drainage system.

Drainage

1. High-survivability drainage applications for geotextiles are where installation stresses

are more severe than moderate applications, i.e., very coarse, sharp angular aggregate is

used, a heavy degree of compaction (>95%) is specified, or depth of trench is greater

than 3m.

2. Moderate-survivability drainage applications are those where geotextiles are used with

smooth graded surfaces having no sharp, angular projections, no sharp angular

aggregates is used, compaction requirements are light, (less than 95%), and trenches are

less than 3m in depth.

Physical requirements or drainage applications

Drainage (cont.)

Geotextile Filter Requirements

Some criteria/requirement in designing geotextile:

Retention:

Ensures that the geotextile

openings are small enough to

prevent excessive migration of soil

particles.

Permeability:

Ensures that the geotextile is permeable enough to allow liquids to pass through without causing significant upstream pressure buildup.

Anti-clogging:

Ensures that the geotextile has adequate openings, preventing trapped soil from clogging openings and affecting permeability.

Survivability: Ensures that the geotextile is strong enough to resist

damage during installation.

Durability: Ensures that the geotextile is resilient to adverse chemical,

biological and ultraviolet (UV) light exposure for the design life of the project.

The specified numerical criteria for geotextile filter requirements depends on the application of the filter, filter boundary conditions, properties of the soil being filtered, and construction methods used to install the filter.

Drainage (cont.)

Fig. 15 Drainage of the structure

Drainage (cont.)

Fig. 16 Drainage of the structure

Drainage (cont.)

Fig. 17 Drainage of the road

Geotextiles filters replace graded granular filters in trench drains to prevent soils from migrating into drainage aggregate or pipes. They are also used as filters below riprap and other armor materials in coastal and river bank protection systems.

Geotextiles and geocomposites can also be used as drains, by allowing water to drain from or through soils of lower permeability. Examples include pavement edge drains, slope interceptor drains, and abutments and retaining wall drains

Filtration

Allowing fluid to pass while preventing mitigation of soil

particle.

Filtration (cont.)

Fig. 18 Filtration process

Laboratory Tests

Mass per unit area,

Thickness,

Tensile strength, and

Hydraulic properties (filtration opening size)

Soil entrapment level and permittivity of

cleaned samples).

Filtration test

Hydraulic Filter Effectiveness

In the long term, geotextile filters must have the same

permittivity as the soil to be drained. Equal

permittivity prevents pressure build up.

For non-woven geotextiles with a thickness of more

than 2.0 mm, the laboratory water permittivity

coefficient is reduced with a factor of 50 (η=0.02), if

the soil to be drained is a coarse silt or sand. In all

other, reduction factor of 100 (η=0.01) is used.

Filtration test

Physical Properties of Fabrics

More dependant on temperature and humidity such as

i. Mass per unit area

ii. Nominal thickness

iii. Compressibility

Mechanical Properties of Fabric

Form the basis for evaluating a geotextile’s

resistance to damage during construction

(fabric survivability) and are related to the

fabric’s ability to support workers and

construction equipment before any fill is

placed (fabric workability).

Mechanical Properties of Fabric

(cont’d)

i. Mechanical properties of fabrics include:

ii. Tensile strength – peak strength and stress-strain

modulus

iii. Burst, tear and impact strength – puncture

resistance

iv. Mechanical durability – loss of strength with time

under particular environmental influences, creep

and abrasion

Property Value(1) Units Test Method(2)

Pore Size

AOS

O95W µm Franzius Institute

O95H µm NFG 38.C17

Permeability m / s SABS 0221-88

Percentage Open Area 5 % Visual Measurement

Porosity-Nonwovens 60 % Calculation

Trapezoidal Tear N ASTM D4533-85

CBR Puncture kN SABS 0221-88

Dart Test mm CPA 1991

Tensile Strength kN / m SABS 0221-88

UV Light Stability (150 hours) 80% strength retained ASTM 4355-84

Geotextile Filter Specification

The required geotextile property values obtained from the desk top

analysis are inserted in the table above. If performance testing is

carried out, the property values of the most suitable, cost effective

geotextile will be applied.

UNIAXIAL TENSION TEST --

GEOTEXTILES

Grab Tensile Test (4 in wide specimen, 25 mm (1 in) grip): ASTM D4632

Narrow Strip Tensile Test (W/L = 1/12; grip width = specimen width): ASTM D 751

ASTM Wide-Strip Tensile Test (W/L = 2/1, 200 mm (8 in) wide specimen): ASTM D 4595

Very Wide Strip Tensile Test (W/L = 2/1, up to 1 m wide)

Grip problems may arise as strength increases

APPLICATIONS WITH CRITICAL

INTERFACE ACTION

Applications using reinforcement function

(involves soil-geosynthetic interface):

Railway and roadway foundations

Earth retaining walls

Reinforced slopes

Waste containment facilities (stability against slippage of liners and covers on slopes)

(involves both soil-geosynthetic and geosynthetic- geosynthetic interfaces)

INTERFACE STRENGTH

= ca + ’n tan

= interface shear strength

c’a = effective interface adhesion

’n = effective normal stress on interface

’= effective interface friction angle

Efficiency

Ec = (ca’/c’) x 100

Ec = (tan’ /tan’) x 100

ADVANTAGES

Nonwoven geotextiles consist of needle

punched short fibres, e.g. UV-stabilised

polyester-fibres, with a pore distribution in

three dimensional direction.

The pore structures of nonwoven geotextiles

(approx. 90% pore volume) behave better

than natural granular filters (approx. 50%

pore volume).

Even if the major part of the pore structure is filled by

soil particles during the lifetime of a coastal structure,

the permeability is not reduced to such an extent that

pressure gradients within the filter layer are noticeable

increased (Kohlhase, 1997).

Long-term stable filter nonwovens have a comparable

ability to deform.

While woven geotextiles are made of sieve like fabrics

which are only two-dimensional oriented, the filtration is

best done with nonwoven fabrics based on their three-

dimensional pore structure.

For coastal protection measures thick nonwovens are proven being resistant against ultraviolet radiation and saltwater (Heerten, 1980).

Additionally, using geotextile sand containers possibly helps to save gravel resources.

Transportation of these materials, which often have to be delivered to the site from distant areas is avoided since classified fill material is not required (Saathoff & Witte, 1994).

DISADVANTAGES High elongation behaviour provides the superior properties

during the construction load case, which is determined as being the biggest risk for damaging the geotextiles.

Conditions during execution of coastal works often play an important role in this context.

This requires mechanical properties such as minimum strength and maximum elongation.

With a reputation of providing high robustness and abrasion resistance, a geotextile container – if possible filled with locally available soil material can be used in nearly every hydraulic construction project where conventionally gravel, stones or rocks are used.

INSTALLATION OF BARRIER

The installation of a barrier component in hydraulic engineering is possible both under dry conditions as well as underwater.

Dry Installation Case:

A conventinal compacted clay as well as Geosynthetic Clay Liner and Geomembrane are commonly used.

Underwater Installation Case:

Need a special composite lining system such as Bentofix BZ 13-B that featuring a sand ballast layer that is integrally encapsulated by needlepunched nonwoven geotextiles.

The sand layer performs several functions which include ballasting Bentofix GCL from floating when installed underwater.

Even where there are currents, or turbulance caused by ship propellers.

Due to the neddlepunching of the Bentofix GCL, the sand layer also has the effect of providing a counter preassure to the natural swealling properties of the clay, providing more uniform activation of the bentonite layer.

UNDERWATER

INSTALLATION

The Bentofix can remain underwater without additional load or cover for longer periods of time, without loss of performance.

Bentofix is suitable for dykes and dams barrier as well as flowing or turbulent inland waters.

Schematic view of overlapping of

Bentofix BZ 13-B

Woven geotextile layer

allows drainage, while

preventing ingress of

capping sand into

rockfill material.

Close-up of woven

geotextile layer and

underlying rockfill.

Geotextile filter in a retaining

wall to prevent the washing

out of fines at the front face.

Geotextile filter ensures that

the fines are not washed out

of the filter dam

Figure 3: The installer unrolled the membrane on the heated tack coat

Figure 4: The contractor compacted the laid membrane

Hafez Geotextile Hafez2009

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