Landfill Liners

Are designed and constructed to create a barrier between the waste and the environment and to drain the leachate to collection and treatment facilities. This is done to prevent the uncontrolled release of leachate into the environment.

Types of Liners

1. Single liners

2. Composite Liners

3. Double Liners

Example of Single Liner System

Example of Composite Liner System

Example of double liner System

GEOSYNTHETICS

Geosynthetics are fabric like material made from polymers such as polyster, polyethylene,polypropylene,polyvinyl chloride(PVC), nylon,chlorinated polyethylene, and others.

THE TERM GEOSYNTHETICS INCLUDE THE FOLLOWING:

1. Geotextile 2. Geomembrane 3. Geonets 4. Georids 5. Geocomposites

Geotextile

Geotextile - Are textile in the traditional sense; However, the fabrics areusually mane from petroleum products such as polyster, polyethylene, and polypropylene.

Geotextile may be;

1. Woven 2. Knitted 3. Nonwoven

Woven Geotextile

Are made of two sets of parallel filaments or strands of yarn systematically interlaced to form a planar structure.

Knitted Geotextile

Are formed by interlocking a series of loopsof one or more filaments or short fiber arranged in an oriented or a random patternin planar structure.

Nonwoven Geotextile

Are formed from filaments or short fibers arranged in an oriented or a random pattern in a planar structure.

  

These FilLamentsare then Bonded by using average or a combination of the following

process:  1.Chemical Bonding – By glue, rubber,

latex, cellulose derivative.2.Thermal Bonding – By heat, for

partial melting of filaments.3. Mechanical Bonding – By needle

punching.

Geotextiles have four major users: Drainage – The fabrics can rapidly

channel water from soil to various outlets.

Filtration – When placed between two soil layers, one coarse grained and the other fine grained, the fabric allows free see page of water from one layer to the other.

Separation – Geotextile help keep various soil layers separate after construction for example, in the construction of highways, a clayey subgrade can be kept separate from a granular base coarse.

Reinforcement – The tensile strength of geotextile increases the load – bearing capacity of the soil.

Cross-Plane Capability

Is generally expressed in terms of a quantity called permittivity,

P = kn t

Where P = Permittivity, se¯¹ or min⁻¹.

kn = Hydraulic conductivity for cross- plane flow, cm/sec of ft/min.

t = Thickness of the Geotextile.

Cross-plane flow Through Geotextile

The In-Plane Drainage Capability Can thus be expressed in terms of a

quantity called transmissivity, which is expressed as, T = kpt

 Where T = Transmissivity, m³/sec or ft³/sec. kp = Hydraulic conductivity for in-plane flow, cm/sec of ft/min.

 

In-plane Flow in Geotextile

Some typical values for kn, P, kp, and T;

Hydraulic conductivity, kn; 1 x 10¯³ to 2-5 x 10¯¹ cm/sec.

Permittivity, P: 2 x 10¯² to 2 – 0 sec¯¹.

Hydraulic conductivity, kp; Non Woven: 1 x 10¯³ to 5x 10¯³ cm/sec. m Woven: 2 x 10¯³ to 4 x 10¯³ cm/sec. m

Geomembranes

Geomembranes - Are impermeable liquid or vapor barriers made primarily from continuous polymeric sheets that are flexible.

Types of Polymeric material used for Geomembrane Thermoplastic Polymers – Include

PYC, polyethylene, chlorinated polyethylene, and polyamide.

Thermoset Polymers – Include ethylene vinyl acetate, polychloroprene, and also preneisobutylene.

Following is a partial list of tests that should be conducted of geomembranes when they are to be used as landfill liners: Density Mass per unit area Water vapor transmission capacity

Tensile behavior Tear resistance Resistance impact Puncture resistance Stress cracking Chemical resistance Ultraviolet light resistance Thermal properties Behavior of seams

Types of Seams

Lap Seam with Adhesive Lap Seam with Gumtape Tongue-and-Groove Splice Extrusion Weld Lap Seam Fillet Weld Lap Seam Double Hot Air or Wedge Seam

Lap Seam with Adhesive

A solvent adhesive is used for this type of seam. After application of the solvent, the two sheets of geomembrane are overlapped, then roller pressure is applied.

 

Lap Seam with Gumtape

This type of seam is used mostly in dense thermo soft material such as isoprene isobutylene.

Tongue-and-Groove Splice

A schematic diagram of the tongue-and-groove splice. The tape used for the splice are double sided.

Extrusion Weld Lap Seam

Extrusion of posion welding is done on geomembranes made from polyethylene. A ribbon of molten polymer is extruding between the two surfaces to be joined.

 

Fillet Weld Lap Seam

This seam is similar to an extrusion weld lap seam, however, for fillet welding, the extrudate is placed over the edge of the seam.

 

Double hot air or wedge seam In hot air seam - Hot air is blown to melt

the two opposing surfaces. For melting, the temperature should rise to about 500°F or more. After the opposite surfaces are melted,pressure is applied to form the seam.

For hot wedge seams - An electricity heated element like a blade is passed between the opposing surfaces of the geomembranes.

 

Double Hot Air or Wedge Seam

Geonets 

Geonets – Are formed by the continuous extrusion of polymeric ribs @ acute angles to each other. - They have large opening in a netlike configuration.

- The primary fuction of geonets is drainage.

Geocomposites

Geocomposites - Are designed to replaceaggregate and/or perforated pipesubsurface drainage systems. A geocomposite consists of a deformed perforated, or slotted plastic core and a geotextile (filter) fabric wrap. Geocomposites include geonets, pavement edge drains (drainage mats), and sheet (wall) drained.

Geogrids

Geogrids Are used for soil reinforcement in embankments and walls, subgrade stabilization, and embankment base reinforcement. Geogrids are characterized by integrally connected elements,with in-plane apertures (openings) uniformly distributed between the elements.

The apertures allow the soil to fill the space between the elements,thereby increasing soil interaction with the geogrid and ensuring unrestricted vertical drainage. The geogrids vary inmanufacturing process, polymer type, coating, density, aperture dimensions, and tensile strength and modulus.

Single Clay Liner and Single Geomembrane Liner

System

Cross-Section of Single Clay Liner System for a Landfill

Cross-Section of Single Geomembrane Liner System for a Landfill

Cross-Section of Double Liner System (Secondary Composite Liner)

Cross-Section of Double Liner System (Primary and Secondary Composite Liner)

End of the Report…

BY: Jestoni G.Elano