Post on 12-Nov-2014
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.
Introduction (cont.)
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).
Introduction (cont.)
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
Introduction (cont.)
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
Introduction (cont.)
Fig. 2 Geogrids
(a) Uniaxial
(b) Biaxial
Introduction (cont.)
Fig. 3 Geomembranes
(a) Smooth
(b) Textured
Introduction (cont.)
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.
Reinforcement (cont.)
Reinforcement (cont.)
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
Reinforcement (cont.)
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.
Reinforcement embankment on
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
Reinforcement embankment on
soft ground (cont.)
Fig. 11 Rotational failure
Fig. 12 Lateral spreading
Reinforcement embankment on
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.
Reinforcement embankment on
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.
Reinforcement embankment on
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
VIT
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