APPLICATION OF GEOTEXTILE INPROTECTION

OFCOSTAL AREA

Presented to :- Prof. R. Alagirusamy

Presented by :- Robin Das

Textile Technology DepartmentIndian Institute of Technology Delhi

Coastal and marine environments are susceptible to erosion, which is caused by the action of waves, tides, currents and other water motion.

To positively influence the morphology and prevent erosion at designed locations a variety of measures are used. Generally, these measures fall into three categories:

Geometrical measures - where the shape of the structure and profile reduce the water forces below a minimum threshold.

Stabilization measures - where the exposed structure is protected from erosion by stabilizing the susceptible soil.

External measures - where the exposed structure is protected from erosion by the provision of a protection structure, placed at some distance.

Introduction

The membranes used in contact with or within soil are termed as geosynthetics.

They are used in sub grade stabilization, soil reinforcement, surface erosion control, subsurface drainage etc.

Geosynthetics (GS) Materials•Geotextiles (GT)

•Geogrids (GG)

•Geonets (GN)

•Geomembranes (GM)

•Geosynthetic clay liners (GCL)

•Geopipe (GP)

•Geofoam (GF)

•Geocomposites (G C)

Geosynthetics

Permeable textile structures made of polymeric materials and are used mainly in civil engineering applications in conjunction with soil, rock or water.

Majority are made from polypropylene fibers Standard textile manufacturing Woven (slit film, monofilament or multifilament) Nonwoven (needle punched or heat bonded) Characterized by an open and porous structure

Geotextile

Unitized, woven yarns or bonded straps

Structure allows for soil “strike-through”

Bidirectional – equal strength in Both directions

Unidirectional – main strength in machine direction

Focuses entirely on reinforcement applications, e.g. Walls, steep slopes, base and foundation reinforcement

All are made from high density polyethylene

Results in parallel sets of ribs as a integral unit

Biplanar – flow is equal in all directions

Triplanar – flow much greater in machine direction

Function is always in-plane drainage Surfaces must be covered; usually

with GTs

Other Geosynthetics

Function is always containment Represents a barrier to liquids and

gases Many types: HDPE, LLDPE, , PVC, EPDM,

etc. Manufactured rolls are field seamed Required by regulations for waste

containment New applications in hydraulics and

private development

Its really buried plastic pipe Function is always drainage HDPE and PVC most

common Both can be smooth walled

or corrugated Corrugated HDPE growth is

enormous

Other Geosynthetics

• Array of available products• GT/GM; GT/GG; GT/GN; etc.• Considerable ongoing innovation• Primary function depends on

final product

• EPS or XPS in block form• lightweight fill on soft or

sensitive soils• relieves lateral pressure on

walls• also used for insulation of

frost sensitive soils

Other Geosynthetics

Role of Geosynthetics

Filters in erosion control structures (revetments, coastal dikes,

etc.)

Separators in the foundation of groins and break- waters,

Fabric forms for sand filled bags or tubes as construction elements

for groins, dikes, and dunes;

Flexible scour protection mats at Different offshore or coastal

structures;

Reinforcement in dredged material sites;

Membranes for use in landfill caps;

Bags for disposing dredged material from navigation channels; and

Dikes for river training and coastal structures.

At present there are several application domains for geotextiles, as reinforcements behind precast concrete seawalls, and under precast erosion control blocks

Application of Geotextile

These geotextiles have exceptional strength due to the high content of a cellulose lignin polymer in them. Besides, they are naturally degradable, which may be attractive in certain applications such as natural stream bank restoration.

Other natural fibers include jute, sisal, mixed coir-jute, and mixed sisal-jute.

Polymers commonly used in the geotextile industry include PE, PP, PVC, PET, PS, PA (nylons), cellulose. Cellulose is a naturally occurring polymer based on glucose as the monomer.

Polymers commonly used in the geotextile industry include PE, PP, PVC, PET, PS, PA (nylons), cellulose. Cellulose is a naturally occurring polymer based on glucose as the monomer.

Another recent development is the use of natural geotextiles, which include fabrics formed using coir, the natural fiber from the husk of coconuts.

Materials used for Geotextile

Costal erosion In addition to sea level rise, there are a number of reasons for the erosion menace that we are witnessing today.

A large number of developmental activities like construction of ports And fisheries harbors

Destruction of mangroves

Beach mining

Unregulated sand mining

Tsunami induced sea bed disturbances

Destruction of sea grass bed, coral reef

mining

Changing wave height and direction due

to climate change

are some of the causes for the shrinking of our coasts.

Global costal erosion scenario It is quite well noticed that about 70% of the coastline of the world is

eroding.

In India, we have a long coastline of about 7500 km including our Islands, and 23% of the coast is eroding

USA, the rate of erosion varies from 0.3 m to 0.6 m/year and approximately 86% of U.S. East Coast barrier beaches have experienced erosion during the past 100 years.

Jiangsu province in China is serious and as high as 85 m/year; in Hangzhou bay the rate is 40 m/year, while in Tianjin it is 16–56 m/year

Nigeria looses land at the rate of 25-30 m/annum

Over the past 15 years, Trinidad and Tobago have reported annual erosion rates of 2-4 m, which is primarily attributed to rising sea levels.

Rates of erosion in Atlantic Canada can reach up to 10 m/year

In Vietnam with average rate of 11 m/year

Japan loses 160 ha of land every year by erosion

Use of geotextile for costal defence Advantage

Replacement of underlayers saving in material, material transport and placement costs

Minimises the amount of “lost” material at the toe where rock buries itself into a soft subsoil

Due to its sheet like qualities reduces differential settlement helping with long term maintenance of alignment of a revetment or breakwater

Use of geotextile for costal defence Disadvantages

It maybe impossible to place geotextiles flat, in position and overlapped in turbid, turbulent water.

Poorly positioned geotextile which has not been properly covered can results in flaps of geotextile being exposed and can cause a danger to shipping by fouling propellers

Whilst geotextiles have a wide range of permeabilities they should not be used where the core material of an embankment is made up of coarse boulders or shingle.

Where frequent rock outcrops occur under water. Placement of cover stone will inevitably pinch and damage the geotextile causing a hole to form and the consequent loss of fines form adjoining soft areas.

The use of geosynthetics for soil confinementThe woven geosynthetics, most of the time made of polypropylene,

are used for the confinement of soils in a variety of marine and hydraulic structures the local soil, generally sand, is placed in a Geosynthetic envelope

these envelopes take one of the following geometrical shapes:

A tubular long structure, filled through injection on site, or Geotube

A submarine structure with a large volume installed with a split bottom hopper barge with a very large sized geotextile bag or Geocontainer

Bags of a small volume or Geobag

Geotube Geocontainer Geobag

Structures for soil confinement Geotube –

A tubular structure is a structure in the form of a tube made of a highly-resistant geotextile woven envelope filled with materials. Sand is the best filling material, mostly due to its incompressibility; but other types of pumpable inert materials can also be used.

Geobags –

Geobag elements are big geotextile bags filled with sand. Geobags are also custom-made and supplied in various forms and sizes. Each unit may typically contain from 1 m3 to over 10 m3 of soil. A special geotextile, capable of retaining the sand materials and allowing at the same time a great permeability, is manufactured for that type of application.

The bag is made of a high-strength geotextile designed according to installation requirement

Geobags

Envelope or Geocontainer –

Envelopes are large-sized geotextile bags containing a great volume of dredged soil or inert materials. They are sank in water by means of a split bottom hopper barge . The envelope is made of a geotextile especially manufactured for that kind of application.

Structures for soil confinement

Containers made from needle-punched nonwoven fabrics have to be used to achieve a higher roughness and thus a better interlocking. The maximal tensile strength according to DIN 53857 is 25kN/m both for the container material and the seams. The characteristic opening size according to EN 12956 is: 0.10≤O90≤0.25 mm.A split bottom hopper barge dropping a geocontainer

Geotube

Design considerations of geotextile tubes

Making use of geotextile tubes, the major design considerations are related to the integrity of the units during release and impact, the accuracy of placement, and the stability under current and wave attack. The following design aspects are of importance.

Properties of the filling material

Mechanical properties of geotextiles

Hydrodynamic stability

Geotube as reclamation dykes Dykes and related structures

typically consist of a general rock fill core and an outer armour protection for long term design against wave and current attacks.

Geotube are placed over the rock fill core to act as filters prior to the construction of the revetment structure. Geotube prevent fines in the rock fill core from being washed out through the porous external revetment cover

Dyke core replacement

‘Pyramid stack’ reclamation dykes

‘Step ladder’ reclamation dykes

Installation of Geotube

Relevant properties for filter/separation

Permeability

Filtration

Extensibility

Puncture resistance.

Thickness

Durability

Water flow normal to the plane EN ISO 11058 – closely linked to

permeability. Water is passed through the geotextile under a

constant head of water.

Pore size EN ISO 12956 – Defines the opening size of a

geotextile and its ability to trap particles and prevent passage.

Minimum tensile extension EN ISO 10319 – defines the total

extension at break in all directions allowing differential

movement without break under the rocks.

Tensile strength EN ISO 10319 – simulates the geotextiles

ability to be handled on site using heavy excavators or

equipment.

The relevant index tests & specification are:

Solution for Costal erosion RevetmentA revetment is a facial or veneer layer applied to the sloping surface of soils to prevent their erosion against wave action and currents. Revetments may be deployed to protect toes of coastal cliffs, bluffs, dunes, etc., and to fortify coastal embankments and flood levees. Revetments reduce wave

reflection.

Absorbs wave energy through a

combination of energy

dissipation within the structure.

Wave run up over the structure

surface.

Different types of revetments is used to prevent the costal erosion

Geotextile implanted revetments are most effective than normal revetments construct only by stones

Because geotextile filter layer prevent erosion of base soil

Revetment

Use of scour and clapping layersScour is the removal of granular bed material by hydrodynamic

forces in the vicinity of hydraulic and marine structures Scour problems can lead to damage of structures e.g. revetments, dykes, seawalls, etc.

The conditions that likely will cause scour problems are as follows:-Breaking waves that impact bottoms Localised increase in orbital velocity due to reflected wavesAccelerated flows due to flow constrictions or structure alignment induced currentsFlow separation and creation of vorticesTransitions from hard bottoms to erodible bedsTo prevent erosion of the seabed Geosynthetics are used as geotextile filters placed on the bed prior to placement of the armour layers.

Estuarial Barriers & BarragesEstuarial barriers and barrages are special dam structures that are designed to hold back the sea during high sea levels while allowing river discharges during normal sea levels

The primary objective of such structures is usually flood prevention

Geotextiles are used as components in prefabricated systems for filtration and reinforcement functions

Coastal Groynes Groynes are finger-like hydraulic structures that jut

perpendicularly out of coastlines. Their engineering function is to interrupt or reduce longshore

sediment transport. This interruption will produce accretion updrift of the groynes and

produce concomitant erosion downdrift of the groynes. Groyne structure is the same as that of a basic dyke structure Geotextiles are used as a filter layer to prevent sand beneath

from being eroded away.

Marinas & JettiesMarinas are areas that are either naturally deep enough for boats to seek shelter within a protected area.

Compared with groynes, jetties extend further offshore into deeper waters.

As a result jetties force littoral bypasses in deeper waters thus preventing channels from silting and inlets from closing off.

geotextiles are used as a filter layer to prevent sand beneath from being eroded away.

Geotube and Geobag may be used to replace the rock fill core of the jetty structures.

Coastal Breakwaters Sheltering and preventing erosion of coastal development

Primary function of sheltering a coastal development by

preventing longshore currents from causing erosion and

reducing wave energies impacting a shoreline

They are connected to the shoreline like groynes and jetties

but differ in function and massiveness.

Additional function of forcing waves to break offshore

geotextiles are used as filter layers for the construction of coastal breakwaters.

Geotube, Geocontainer Geobag may be used to replace the rock fill core of breakwaters.

Offshore BreakwatersOffshore breakwaters are marine structures that have the primary function of reducing wave energies impacting a shoreline.

Offshore breakwaters reduce wave energies by partially reflecting some wave energy seawards.

Offshore breakwaters are generally constructed parallel to shorelines

geotextiles can be prefabricated onshore into a large panel of fascine mattress that can be floated out to sea

This panel of fascine mattress can then be ballasted into position on the seabed by dropping rock onto the floating fascine mattress

Conclusion

The use of geotextiles in coastal areas has been practiced for a very long time for shore protection needs. However, advances in manufacturing and marketing has led to innovative uses of geotextiles in the coastal zone in recent years. These include the use of sand filled Geobags as the core of dunes, sand filled Geobag breakwaters and reefs, Geobag spur dikes, and deep ocean placement of contaminated sediments in Geobags.The future of the geotextile seems limited only by human imagination

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263 ,Australian and German experiences on the use of geotextile containers .

2. INDIAN J. MAR. SCI., VOL. 39 No. 4, DECEMBER 2010, Coastal erosion and mitigation methods – Global state of art .

3. E.C. Shin, Y.I. Oh / Geotextiles and Geomembranes 25 (2007) 264–277 ,Coastal erosion prevention by geotextile tube technology

4. P.V. Long et al. / Geotextiles and Geomembranes 25 (2007) 311–323 ,Geosynthetics reinforcement application for tsunami reconstruction: Evaluation of

interface parameters with silty sand and weathered clay .

5. D SHERCLIFF ,GEOSYNTHETICS IN COASTAL APPLICATIONS: PROTECTION, FILTRATION AND PLACEMENT ISSUES .

6. A. Koffler : A. Bendriss : E. Zengerink Ten Cate Geosynthetics Europe, Paris, France ,Geosynthetics in protection against erosion for river and coastal banks and

marine and hydraulic construction

7. Eugeni~z Dernbicki, Lucyna Niespodzitiska /Geotextiles and Geomembranes 10

(1991) 147-159 , Geotextiles in Coastal Engineering Practice .