This presentation introduces the different types of Geosynthetics, their functions and applications. its very informative and will form a good foundation to anyone interested in this versatile technology.
Introduction to Geosynthetics Types and Applications_Sirmoi Wekesa
Republic of Kenya
Ministry of Transport &Infrastructure,
Department of Infrastructure,
Materials Testing & Research Division,
Studies on Geosynthetics Reinforced
November 2013: Technical Presentation – Session I
Prepared and Presented by Sirmoi Wekesa
Kensetsu Kaihatsu Ltd
Civil Engineering Contractors, Consultants, Architects & Planners, Interior Designers
Introduction to Geosynthetics:
Type and Applications
2. Different types of geosynthetics
3. Main functions of geosynthetics
4. Major applications of geosynthetics
5. Major benefits of geosynthetics
What is a Geosynthetic
A planar product manufactured
from polymeric material used
within geomaterials to enhance
geotechnical engineering/geostructural properties through
Geosynthetics is a generic term for
all synthetic materials used in
applications including geotextiles,
geogrids, geomembranes, geocells,
geocomposites, geonets etc.
TYPES OF GEOSYNTHETICS
A geosynthetic formed by a
regular network of tensile
elements and apertures,
typically used for
Categorized by the method/mode
Punched and Extruded Geogrids
Categorized by the orientation of
A geotextile/geofabric is a permeable
textile used with foundation, soil,
rock, earth, or any other geotechnical
engineering-related materials as an
integral part of a human-made
project, structure, or system.
Geonets are made of stacked, criss-crossing
polymer strands that provide in-plane
Nearly all geonets are made of
Two layers of strands are called “bi-planar”.
Three layers are called “tri-planar”.
These are products manufactured by
combining the superior features of
various types of geosynthetics.
The objective is to produce materials
which are multi-functional and are
faster to install than the individual
Interface friction becomes an issue
when geosynthetics are placed on
slopes and bonded materials address
this potential problem.
CLAY LINERS [GCLs]
Geosynthetic clay liners (GCLs)
include a thin layer of finely-ground
bentonite clay. When wetted, the
clay swells and becomes a very
effective hydraulic barrier.
sandwiching the bentonite within
or layering it on geotextiles and/or
geomembranes, bonding the layers
with needling, stitching and/or
TYPES OF GEOSYNTHETICS
6. GEOCELLULAR CONFINEMENT
Geocellular confinement systems
(GCS) are 3-dimensional honeycomblike structures filled with soil, rock or
The GCS structure, often called a
Geocell, is made of strips of polymer
sheet or geotextile connected at
staggered points so that, when the
strips are pulled apart, a large honeycomb mat is formed.
The GCS provides both a physical
containment of a depth of soil and a
transfer of load through
Geomat is a three-dimensional erosion
control mat consisting of a UV-stabilized
labyrinth-like extruded polymer core
mounted on a warp knitted mesh
The Geomats act in three major
Surface reinforcement and confinement of
Protection against rain drops
Reinforcement of the slope and at the same
time allowing vegetation [grass] growth
Another significant product
which has been “adopted” as a
geosynthetic is plastic pipe.
There is a wide variety of civil
engineering applications for
these products, including:
highway and railway edge drains,
interceptor drains, and
leachate removal systems.
Geofoam is manufactured into
large blocks which are stacked to
form a lightweight, thermally
insulating mass buried within a
soil or pavement structure.
Typical applications of geofoams
within soil embankments built over
soft, weak soils;
under roads, airfield pavements
and railway track systems subject to
excessive freeze-thaw conditions;
beneath on-grade storage tanks
containing cold liquids.
5. Erosion Control
REDUCTION OF STRESS
The stresses over the subgrade are higher in
unreinforced flexible pavements than in
geosynthetic-reinforced pavement due to
stress distribution factor
1Relative Load Magnitudes at
Subgrade Layer Level for:
(a) Unreinforced Flexible Pavement;
(Improved) Flexible Pavement.
INTEGRAL MECHANISMS THAT
Geosynthetics provide reinforcement through
three possible mechanisms.
Lateral restraint of the base and
subgrade through friction and
interlock between the aggregate, soil
and the geosynthetic .
Increase in the system bearing
capacity by forcing the potential
bearing capacity failure surface to
develop along alternate, higher shear
Membrane support of the wheel
INTEGRAL MECHANISMS THAT
Reinforcement Mechanisms Induced by Geosynthetics: (a) Lateral Restraint (b)
Increased Bearing Capacity; and, (c) Membrane Tension Support
Preventing intermixing of soil types
or soil/aggregate to maintain the
integrity of each material yet still
allow the free passage of
liquids/gases. Commonly used in
between sub-base/subgrade and
around drainage materials.
Contamination of the base course
layers leads to a reduction of
strength, stiffness and drainage
characteristics, promoting distress
and early failure of roadway.
Restraining soil particles subject
to hydraulic forces whilst
allowing the passage of
liquids/gases. This function is
often partnered with separation.
Allowing fluids and gases to flow
both through the plane of the
material. Commonly used as
components in geocomposites
used for surface water runoff or
for gas collection under
Influencing Filter, Separation
and Drainage Functions
Piping Resistance: Apparent
Opening Size - AOS (as related to
Permeability: Flow capacity, and
Strength and Durability: Grab,
Isolating one material form another.
The most frequent use of this
function is in landfills where
impermeable linings prevent
contamination of surrounding soils
Preventing or limiting localized
damage to an adjacent material,
usually a geomembrane used to line
a lagoon or a landfill. Thick
geotextiles prevent puncture or
excessive strain in the membrane.
5. EROSION CONTROL:
Protecting and reinforcing slopes
and drainage channels from
erosive agents whilst allowing
the establishment of vegetation
Subgrade Separation and Stabilization;
1. GEOSYNTHETICS IN
ROADS AND PAVEMENTS:
Overlay Stress Absorption and
Separation refers to the ability of a
Geosynthetics to provide and
maintain physical separation between
the base course aggregate and the
underlying fine grained subgrade.
It does prevent mixing of the two
dissimilar materials, where mixing is
caused by mechanical action
generally induced by construction
and operation traffic.
The ingress of fines by as little as 10%
by weight results in the reduction of
strength by more than 80%.
Characteristics of Pavement Structure Subjected to Black Cotton Soil Intrusion
After Repeated Dynamic Loading and Cyclic Seasonal Effects
ANALYSIS OF IMPACT OF INFERIOR MATERIAL INTRUSION INTO UPPER
Optimum Batching Ratio
Reduction in CBR Practically Linear
Rate of Reduction and Reduction Characteristics Dependent
on Batching Ratio and Quality of Bearing Material
Lower Bound Limits are Distinctly Dependent on
CBR Reduction ~ PI Threshold @PI =40%
Tendency to Residural (Threshold)
Plasticity Index, PI (%)
Impact of Black Cotton Soil
Impact of Varying Geomaterial
Stabilization of weak subgrades entails the
confinement and mechanical interlocking
of aggregates within the apertures of the
geosynthetics to increase the bearing
The three main important functions of
Lateral restraint is the lateral interaction
between the aggregate and the geosynthetic.
The presence of the geosynthetic creates
pressure in the aggregate that improves the
strength and stiffness of the road structure.
Membrane action is the ability of a geosynthetic
material to reduce and spread stress arising
from the weak subgrade. Additionally, when a
geogrid is involved, a third function can be
enhanced load distribution within the
Base Reinforcement is achieved through
lateral restrain [confinement].
With the addition of an appropriate
geosynthetic, the Soil-GeosyntheticAggregate (SGA) system gains stiffness.
The stiffened SGA system is better able to
provide the following structural benefits:
Preventing lateral spreading of the base
Increasing confinement and thus stiffness of the
Improving vertical stress distribution on the
Reducing shear stress in the subgrade
OVERLAY STRESS ABSORPTION
A geosynthetic interlayer can be placed
over the distressed pavement or within the
overlay to create an overlay system. The
geosynthetic interlayer can contribute to
the life of the overlay via stress absorption,
strain relief and provision of tensile
A stress relieving interlayer retards the
development of reflective cracks by
absorbing the stresses that arise from the
damaged pavement. It also waterproofs
the pavement so that when cracking does
occur, water ingress cannot worsen the
Reinforcement occurs when an interlayer
is able to contribute significant tensile
strength to the pavement system. The
reinforcement attempts to prevent the
cracked old pavement from moving under
traffic loads and thermal stress by holding
the cracks together.
The benefits of geosynthetic interlayers
Reduction of overlay thickness
Delaying the appearance of reflective cracks
Lengthening the useful life of the overlay
(MODEL TESTING) – ASPHALT
Propagation of the primary crack in non-reinforced sample
Interlayer bonding level of the binder and wearing course (the level of the reinforcement)
Propagation of the primary crack in the geocomposite reinforced sample
Propagation of the secondary crack in the geocomposite reinforced sample
Propagation of the primary crack in the geogrid reinforced sample
Reference lines for observations of crack
Average test temperature T± 2σ:
non-reinforced sample T=13,2 ± 0,4°C
reinforced sample T=13,4 ± 0,7°C
Number of the cycles
2. GEOSYNTHETICS IN
Road Base Drainage, and
A high groundwater table can, and often
does, interfere with the stability of subgrade
soils. For instance, some clay soils can swell or
shrink as their water content increases or
Geosynthetic materials have become
commonplace in subsurface drainage
applications. Commonly, geotextiles are
being used in lieu of select grades of sand
because they are less expensive, provide
more consistent properties, and are much
easier to install.
The introduction of geotextiles into drainage
applications has enhanced the economical
application of blanket and trench drains
under and adjacent to the pavement
ROAD BASE DRAINAGE : The excellent filtration and separation
characteristics associated with filtration
geotextiles permits the use of a single layer of
open-graded base or trench aggregate
enveloped in a geotextile.
It has become customary to place a
vertical blanket of “pervious” sand or
gravel behind retaining walls for
protection against hydrostatic pressures.
STRUCTURE DRAINAGE :
One of the best ways to assure effective
aggregate drainage is to sandwich an
aggregate layer within layers of filtration
geotextiles. The inclusion of a perforated
drain pipe that collects and discharges
seepage will increase the drain’s
efficiency. Back fill is placed directly
against the drain.
3. GEOSYNTHETICS IN
EROSION AND SEDIMENT
Channel Protection, and
GEOSYNTHETICS IN EROSION AND SEDIMENT CONTROL:
Embankments over Soft Foundations;
Reinforced Steepened Slopes; and
4. GEOSYNTHETICS IN
REINFORCED SOIL SYSTEMS: Mechanically Stabilized Earth Walls
The primary problem with these soft soils results from
their low shear strength and excessive consolidation
settlements requiring special construction practices and
leading to high construction costs.
Several methods of treatment are available to reduce the
problems associated with soft foundations. These
SOFT FOUNDATIONS :
Removal and replacement of soft soil.
Displacement of compressible material by end-loading.
Staged construction - placing fill at controlled rates to allow
for consolidation and strength gains.
Installation of drains to facilitate consolidation.
Pre-loading the site to reduce settlements of the structure
and provide higher strength.
Deposit improvement using admixtures (e.g. soil, cement,
lime) or injections
Reinforcement of the soil matrix using a structural element.
SOFT FOUNDATIONS :
soil reinforcement has emerged as an efficient,
economical and effective solution to the problem
of constructing embankments over soft soils.
For many years, retaining structures were almost
exclusively made of reinforced concrete and were
designed as gravity or cantilever walls which are
essentially rigid structures and cannot
accommodate significant differential settlements
unless founded on deep foundations.
The economic advantages of constructing a safe,
steeper RSS than would normally be possible are
the resulting material and rights-of-way savings.
For example, in repair of landslides it is possible
to reuse the slide debris rather than to import
higher quality backfill.
Summary of Benefits categorized into Structural and
Benefits Based On Study Findings
Enhanced geotechnical engineering properties including
bearing capacity, structural capacity, shear strength and
deformation resistance [achievement of higher
resilient/elastic modulus (stiffness)].
Increased ranges of permissible resilient/linear elastic and
Improvement of the subgrade strength and deformation
resistance through stress mobilization and expanded
distribution, as well as further tension cut-off.
By spreading and distributing the imparted stresses over a
wider area of the foundation, geosynthetics may be
improving the foundation/subgrade in a mode that is
analogous to stage loading consolidation.
Enhanced structural performance resulting from increased
resistance to deformation.
Prevention of the migration of inferior material into the
upper pavement layers. This results in the significant
enhancement of structural performance and elongation of
the life-span of the pavement structure.
Structural benefits analyzed and realized on
the basis of theoretical considerations and
experimental data determined in this Study
VALUE ENGINEERING BENEFITS
Appropriate application of geosynthetics can
realize the following benefits.
Construction cost-time savings through
the reduction of required pavement
material quantities, whilst maintaining
enhanced structural performance.
Elongated pavement structural life –
span particularly as a result of
incorporating the filtration/separation
Reduction in maintenance
requirements as a result of enhanced
Environmental conservation mainly due
to reduction in material quantities and