Geosynthetics
Nanjundaswamy P. Dept. of Civil Engineering S J C E, Mysore What are Geosynthetics?
GEO Soil, Rock or other Geotechnical material SYNTHETIC Man made Polymeric material Used to enhance, augment and make possible cost effective construction Polymer - Types & Materials
Polypropylene(PP) Polyethylene (HDPE, LDPE, LLDPE) Polystyrene (PS) Polyvinyl Chloride (PVC) Polyamide (PA) eg. Nylon Polyester Acrylonitrile Butadiene Styrene (ABS) Roles or Functions of Geosynthetics
. Separator
. Reinforcement
. Drainage
. Filter
. Energy absorber
. Container
. Barrier Geosynthetic Global Offer Types of Geosynthetics
Geotextiles (GT) Geogrids (GG) Geonets (GN) Geomembranes (GM) Geosynthetic clay liners (GCL) Geocomposites (GC) Geo others Geopipe, Geofoam, Geocells, Geomesh Geotextiles (GT) Geotextiles (GT)
Flexible, textile-like fabrics Majority are made from polypropylene fibers Woven (slit film, monofilament or multifilament) Nonwoven (needle punched or heat/chemical bonded) Characterised by an open and porous structure (with controlled permeability) Mechanical and Hydraulic properties vary widely Very versatile in their primary function (except as liquid barrier) Geogrids (GG) Geogrids (GG) stiff or flexible polymer grid-like sheets 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 Geonets (GN) Geonets (GN) 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 Geomembranes (GM) Geomembranes (GM) impermeable sheets (10-11 to 10-13 cm/s) function is always containment represents a barrier to liquids and gases many types: HDPE, LLDPE, fPP, PVC, EPDM, etc. manufactured rolls are field seamed new applications in hydraulics and private development Geosynthetic Clay Liners (GCL) Geosynthetic Clay Liners (GCL) function is always containment common product is bentonite between 2-GTs internally reinforced by needle punched or stitching bentonite product bonded to GM is also available many other variations exist competitive with compacted clay liners (CCLs) beneath a GM; one has a composite liner Geopipe (GP)
GEOPIPE Geopipe (GP) its really buried plastic pipe! function is always drainage HDPE and PVC most common can be smooth walled or corrugated corrugated HDPE growth is enormous Geofoam (GF)
GEOFOAM Geofoam (GF) lightweight fill on soft or sensitive soils relieves lateral pressure on walls also used for insulation of frost-sensitive soils Geocomposites (GC) Geocomposites (GC) hybrid systems of any or all array of available products GT/GM; GT/GG; GT/GN; etc. considerable ongoing innovation primary function depends on final product Function vs. Geosynthetic Type
Type of Separation Reinforcement Filtration Drainage Containment Geosynthetic geotextile geogrid
geonet geomembrane geosynthetic clay liner geopipe geofoam geocomposite Properties of Geosynthetics - Parameters
Physical Chemical Mechanical Hydraulic Endurance Degradation Parameters . . . .
Physical Thickness Specific Gravity Mass per unit area Porosity Percent open area Apparent opening size Parameters . . . .
Chemical Polymer type Filler material Carbon black percentage Plasticizers and additives Manufacturing process Parameters . . . .
Mechanical Tensile strength Compressibility Elongation Tear/impact/puncture resistance Burst strength Seam strength Fatigue resistance Interface friction with soil Anchorage in soil Parameters . . . .
Hydraulic Permittivity (cross plane permeability) Transmissivity (in plane permeability) Clogging potential Parameters . . . .
Endurance Installation damage potential Tear/impact/puncture resistance Abrasion resistance creep Parameters . . . .
Degradation Resistance against Ultraviolet radiation Temperature Oxidation Aging Chemical and Biological reactions Properties of Geosynthetics Range of Values
Mass per Tensile Apparent Thickness Elongation Type unit area strength opening size (mm) (%) (gsm) (kN/m) (mm) Non-Woven 0.25 – 7.5 100 – 2000 5 – 100 20 – 100 0.02 – 0.6 Geotextile Woven 0.25 – 3.0 100 – 1500 20 – 400 10 – 50 0.05 – 2.0 Geotextile
Geomebranes 0.25 – 3.0 250 – 3000 10 – 50 50 – 200 ~ 0
Geogrids 5.0 – 15.0 200 – 1500 10 – 200 5 – 25 10 – 100
Geonets 3.0 – 10.0 100 – 1000 – – 5 – 15 Functional requirements
Separation High tensile strength (20 – 400 kN/m) Allow flow of water but no mixing of soil High burst strength High tear/impact/puncture resistance
Geotextiles (usually woven) Functional requirements . . . .
Filtration Cross-plane permeability higher than base soil (10e-5 to 1 m/s) Pore size small enough to enable retention of fines (95% pore size – 0.02 to 2.0 mm) Low clogging potential
Geotextiles (usually non-woven) Functional requirements . . . .
Drainage Requirements of filtration High in-plane permeability
Geotextiles (thick non-woven) Geonets sandwiched b/w geotextiles (Geocomposite sheet drain) Functional requirements . . . .
Reinforcement High tensile strength Low elongation (high stiffness) (5 to 25%) High shearing resistance along soil reinforcement interface
Geotextiles (low elongation) Geogrids Functional requirements . . . .
Barrier High imperviousness (10e-12 to 10e-15 m/s) Leakproof welding along seams No slippage when laid along sloping ground
Geomebranes