GEOTEXTILES IN TRANSPORTATION APPLICATIONS 1 GEOTEXTILES IN TRANSPORTATION APPLICATIONS

INTRODUCTION Defined as permeable textile materials used in contact with the soil, rock, earth etc as an integral part of civil engineering project, structure, or system

FUNCTIONS OF GEOTEXTILES Filtration Drainage Separation Reinforcement Sealing

SEPARATION The introduction of a flexible porous textile placed between dissimilar materials so that the integrity and functioning of both the materials can remain intact or be improved

FILTRATION The equilibrium geotextile to soil system that allows for adequate liquid flow with limited soil loss across the plane of geotextile over a service lifetime.

DRAINAGE/TRANSMISSIVITY Ability of thick nonwoven geotextile whose 3- dimensional structure provides an avenue for flow of water through the plane of the geotextile

REINFORCEMENT Improvement in the total system strength created by the introduction of geotextile into soil Three mechanisms involved:-

SEALING The classic application of a geoxtile as a liquid barrier is paved road rehabilitation It minimizes vertical flow of water into the pavement structure

TYPES OF GEOTEXTILES Woven fabrics Non-woven fabrics Knitted fabrics

DESIGN PROPERTIES Puncture Strength Burst Strength Dynamic Puncture Permeability Apparent Opening Size (AOS) Grab Tensile Strength and Elongation

Puncture Strength to measure puncture resistance stimulates puncture strength to static load of aggregates resistance to puncture measured in Newton

Burst Strength stimulates strength of geotextile to a continuous hydraulic load force causing rupture recorded in units of pounds per square inch or Kilo Pascal

Dynamic Puncture to measure the strength of geotextile to falling objects stimulates placement of aggregate over geotextile during installation stage expressed in mm

Permeability measures the rate at which liquids can pass through the geotextile x=k/t x- geotextile permittivitty (sec-1) k- geotextile permeability(cm/sec) t- geotextile thickness (mm) expressed in liters per square meters per second

Apparent Opening Size (AOS) Reflects approximate largest opening dimension available through which the soil may pass. expressed in mm

Grab Tensile Strength and Elongation Measures tensile strength and elongation along the plane of the geotextile by loading it continually Value of breaking load expressed in Newton and elongation at break in percent

AREAS OF APPLICATION Flexible paved road construction Drainage applications Pavement overlays

Flexible paved road construction Function of geotextiles:- service life of roads load carrying capacity rutting

Researches on Geotextile For weak subgrades (CBR=2%) Service life by a factor of 2.5-3.0 AASHTO structural number by 19% For moderate strength (CBR=4.2-4.5%) Service life by a factor of 2.0-3.3 AASHTO structural number by 13-22%

AASHTO DESIGN METHOD SNeff Drainage factor - 1.20 poor drainage excellent drainage SNeff Drainage factor - 1.20 poor drainage Drainage factor as 0.60

Geotextile Requirement Selection of geotextile:- depends on survivability governed by anticipated construction stresses

Pavement Overlays Benefits of using Fabric Interlayer waterproofing of the lower layers retarding reflection cracking in the overlay increase in structural stability absorption of stresses

Capabilities of Paving Fabrics:- Reduces permeability of a pavement Reduces infiltration of moisture Maintains the strength of subgrade, sub base and base course Limiting damage due to saturated condition pore pressures

Properties of Paving Fabrics:- Nonwoven fabrics from grades ranging from 135gm/m² to 200gm/m² Lighter fabrics are moisture barriers Heavier fabrics provides cushioning or stress- relieving membrane

Installation Procedure the surface is cleaned cracks are filled or repaired tack coat ranging from 1-1.35 l/m² of residual asphalt is evenly applied the paving fabric is laid with minimum wrinkles finally hot mix overlay is placed

Drainage by providing relatively unimpeded flow of water Drainage system should fulfill 2 criteria:- Have maintained permeability by providing relatively unimpeded flow of water Filtration of base soil by preventing the migration of soil fines into the drain

CONCLUSION Geotextiles are an efficient effective and economic method of solving most of the geotechnical problems in roads. The design engineer should be well aware of the possible problems and should use this relatively new tool for solving them. For this he/she should understand properties and capabilities of the geotextile material.

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