intro to geosynthetics

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  • 11/13/2014

    1

    Studies on Geosynthetics Reinforced Materials

    Prepared and Presented by Mike Baylon

    Introduction to Geosynthetics: Type and Applications

    Session I

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    1. Preamble

    2. Different types of geosynthetics

    3. Main functions of geosynthetics

    4. Major applications of geosynthetics

    5. Major benefits of geosynthetics

    Presentation guidelines

    A planar product manufactured from polymeric material used within geomaterials to enhance geotechnical engineering/geo-structural properties through reinforcement and/or improvement.

    Geosynthetics is a generic term for all synthetic materials used in geotechnical engineering applications including geotextiles, geogrids, geomembranes, geocells, geocomposites, geonets etc.

    What is a Geosynthetic

    material?

    Preamble

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    TYPES OF GEOSYNTHETICS

    A geosynthetic formed by a regular network of tensile elements and apertures,

    typically used for reinforcement purposes

    1. GEOGRIDS

    1. GEOGRIDS

    Type 1:

    Categorized by the method/mode of manufacturing:

    Triaxial Geogrids Biaxial Geogrids

    Punched and Extruded Geogrids

    Welded Geogrids

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    GEOGRIDS

    Type 2:

    Categorized by the orientation of ribs

    Uniaxial Geogrids

    Triaxial Geogrids Biaxial Geogrids

    Quaxial Geogrids

    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.

    2. GEOTEXTILES

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    2. GEOTEXTILES Type:

    Woven Geotextiles

    Non-woven Geotextiles

    Uniaxial Geogrids

    Geonets are made of stacked, criss-crossing polymer strands that provide in-plane drainage.

    Nearly all geonets are made of polyethylene.

    Two layers of strands are called bi-planar.

    Three layers are called tri-planar.

    3. GEONETS

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    3. GEONETS Type:

    Biplanar

    Triplanar

    Biplanar Geonets

    Triplanar Geonets

    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 components.

    Interface friction becomes an issue when geosynthetics are placed on slopes and bonded materials address this potential problem.

    4. GEOCOMPOSITES

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    4. GEOCOMPOSITES

    Geocomposites

    Geomembranes are relatively impermeable sheets of plastic.

    5. GEOMEMBRANES

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    5. GEOMEMBRANES

    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.

    GCLs are manufactured by sandwiching the bentonite within or layering it on geotextiles and/or geomembranes, bonding the layers with needling, stitching and/or chemical adhesives.

    6. GEOSYNTHETICS

    CLAY LINERS [GCLs]

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    6. GEOSYNTHETICS CLAY LINERS

    TYPES OF GEOSYNTHETICS

    Geocellular confinement systems (GCS) are 3-dimensional honeycomb-l ike structures fi l led with soil, rock or concrete.

    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 honey-comb mat is formed.

    The GCS provides both a physical containment of a depth of soil and a transfer of load through

    6. GEOCELLULAR CONFINEMENT

    SYSTEMS

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    6. GEOCELLULAR CONFINEMENT

    SYSTEMS

    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 mechanisms:

    Surface reinforcement and confinement of the soil;

    Protection against rain drops

    Reinforcement of the slope and at the same time allowing vegetation [grass] growth

    7. GEOMATS

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    7. GEOMATS

    Biodegradable Geomats

    Non-biodegradable Geomats

    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.

    8. GEOPIPES

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    8. GEOPIPES

    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 include:

    within soil embankments built over soft, weak soils;

    under roads, airfield pavements and railway track systems subject to excessive freeze-thaw conditions; and

    beneath on-grade storage tanks containing cold l iquids.

    9. GEOFOAMS

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    9. GEOFOAM

    Main Functions Of Geosynthetics

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    1. Reinforcement

    2. Filtration

    3. Separation

    4. Drainage

    5. Erosion Control

    6. Barrier/Protection

    Main Functions:

    1. REINFORCEMENT: RED UCTION OF STRESS

    INTENSITY (CONCENTRATION) TH ROUGH WIDER

    D ISTRIBUTION

    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; and,

    (b) Geosynthetics-Reinforced (Improved) Flexible Pavement.

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    INTEGRAL MECHANISMS THAT CONTRIBUTE TO PERF ORMANCE

    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 strength surfaces.

    Membrane support of the wheel loads.

    Geosynthetics provide reinforcement through

    three possible mechanisms.

    INTEGRAL MECHANISMS THAT CONTRIBUTE TO PERF ORMANCE

    Reinforcement Mechanisms Induced by Geosynthetics: (a) Lateral Restraint (b)

    Increased Bearing Capacity; and, (c) Membrane Tension Support

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    Aperture Stability

    Aperture Size

    Junction Integrity

    Radial stiffness

    Geosynthetics Characteristics

    Influencing Reinforcing

    Functions

    2. SEPARATION: 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.

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    SEPARATION MECHANISMS

    3. FILTRATION: Restraining soil particles subject

    to hydraulic forces whilst allowing the passage of

    liquids/gases. This function is often partnered with separation.

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    4. DRAINAGE: 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 membranes.

    Piping Resistance: Apparent Opening Size - AOS (as related to soil retention),

    Permeability: Flow capacity, and clogging potential.

    Strength and Durability: Grab, Puncture strengths

    Geosynthetics Characteristics

    Influencing Filter, Separation

    and Drainage Functions

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    5. BARRIER/PROTECTION:

    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 cover.

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    Major Applications of Geosynthetics

    1. GEOSYNTHETICS IN ROADS AND PAVEMENTS:

    Subgrade Separation and Stabilization;

    Base Reinforcement;

    Overlay Stress Absorption and

    Overlay Reinforcement

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    SUBGRADE SEPARATION

    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 l ittle 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

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