BMT

Geotextiles

1. Introduction

Geotextiles are permeable fabrics made from synthetic or natural fibers used in civil engineering applications to improve soil behavior, provide separation, filtration, drainage, reinforcement, and protection. They are part of the broader family of geosynthetics, which also includes geomembranes, geogrids, geonets, and geocomposites.

Commonly used polymers:

• Polypropylene (PP)
• Polyester (PET)
• Polyethylene (PE)
• Polyamide (Nylon)

2. Functions of Geotextiles

Function	Description	Example Application
Separation	Prevents mixing of two different materials (e.g., subgrade soil and aggregate)	Road construction between subgrade and sub-base
Filtration	Allows water to pass while retaining soil particles	Drainage trenches, retaining walls
Drainage	Facilitates lateral flow of water within the fabric	Behind retaining walls, under roads
Reinforcement	Provides tensile strength to weak soils	Embankments, retaining structures
Protection	Protects geomembranes from puncture and mechanical damage	Landfill liners, waterproofing membranes

3. Types of Geotextiles

Type	Manufacturing Method	Structure	Properties	Typical Uses
Woven	Interlacing of warp and weft yarns	Regular pattern	High tensile strength, low elongation	Reinforcement, separation
Non-woven	Bonding of randomly oriented fibers (needle-punched or heat-bonded)	Felt-like	High permeability, good filtration	Filtration, drainage
Knitted	Interlocking of loops of yarn	Flexible	Moderate strength and elongation	Specialized reinforcement
Composite Geotextiles	Combination of woven and non-woven	Layered	Combines functions of both types	Multifunctional uses

4. Raw Materials and Properties

Property	Polypropylene (PP)	Polyester (PET)	Polyethylene (PE)
Density (g/cm³)	0.91	1.38	0.95
Tensile Strength	Moderate	High	Low
Chemical Resistance	Excellent	Good	Excellent
UV Resistance	Fair	Good	Fair
Creep Resistance	Excellent	Good	Moderate
Moisture Absorption	Negligible	Slight	Negligible

Note:

• PP geotextiles are widely used in roads and embankments.
• PET geotextiles are preferred in high-strength and temperature-stable applications.

5. Mechanisms of Action

5.1 Separation

• Geotextile acts as a barrier between two dissimilar materials (e.g., soft subgrade and granular base).
• Prevents intermixing, ensuring stability and load distribution.
• Common in pavement layers, railway tracks, and embankments.

5.2 Filtration

• Allows water to flow perpendicular to the fabric while retaining soil particles.
• Maintains hydraulic continuity without soil loss.
• Used in drainage systems, riverbanks, and retaining walls.

5.3 Drainage

• Permits lateral flow of water within the fabric plane.
• Used for subsurface drainage, landfills, and backfills.

5.4 Reinforcement

• Provides tensile resistance to soils lacking strength.
• Mobilizes tensile forces to distribute loads over a wider area.
• Used in steep slopes, retaining walls, and embankments on soft soils.

5.5 Protection

• Serves as a cushion or separator layer to prevent puncture or abrasion of waterproof membranes or geomembranes.

6. Applications of Geotextiles

Field	Specific Application	Function
Highway Engineering	Separation between subgrade and base; drainage	Separation, filtration
Railway Engineering	Track stabilization, separation	Reinforcement
Embankments and Slopes	Stability improvement on soft soils	Reinforcement
Erosion Control	Under riprap or gabions	Filtration, protection
Drainage Systems	Vertical and horizontal drainage	Filtration, drainage
Landfills	Cushion layer over geomembrane	Protection
Canal and Dam Linings	Filtration layer beneath riprap	Filtration
Tunnels and Underground Works	Drainage layer between rock and concrete	Drainage

7. Design Considerations

• Permeability ratio (kf/ks): The geotextile permeability ( k_f ) must be greater than the soil permeability ( k_s ) to prevent clogging.

• Retention criteria: The apparent opening size (AOS or O95) should be small enough to retain soil but large enough to allow drainage.

• Strength criteria: Based on tensile strength, puncture resistance, and seam strength depending on loading and installation conditions.

• Durability: Must resist degradation due to UV radiation, chemicals, biological activity, and installation damage.

8. Installation Practices

1. Surface Preparation

   • Level and compact subgrade.
   • Remove sharp objects or debris.

2. Laying of Geotextile

   • Unroll fabric smoothly without wrinkles.
   • Overlap joints typically 300–450 mm, depending on site conditions.

3. Anchoring and Joining

   • Use pins, adhesives, or heat welding for joining.
   • Overlaps secured to prevent displacement during filling.

4. Placement of Fill Material

   • Spread fill in thin layers to avoid tearing.
   • Avoid direct contact of heavy equipment with geotextile.

5. Inspection and Quality Control

   • Check for tears, overlaps, and alignment before covering.

9. Testing and Quality Control

Property	Test Method	Reference Standard
Mass per unit area	Gravimetric	IS 14716 / ASTM D5261
Tensile strength & elongation	Wide width tensile test	IS 13162 (Part 5) / ASTM D4595
Permittivity	Constant head test	ASTM D4491
Apparent opening size (AOS)	Dry sieving	ASTM D4751
Puncture resistance	CBR puncture test	IS 16391 / ASTM D6241
UV Resistance	Accelerated weathering test	ASTM D4355

10. Advantages of Geotextiles

• Lightweight and easy to install.
• Durable and resistant to chemical/biological attack.
• Reduces need for graded filter layers.
• Enhances stability and service life of structures.
• Economical and sustainable (reduces natural aggregate usage).

11. Limitations

• Vulnerable to UV degradation when exposed.
• May clog in fine silty soils without proper selection.
• Requires careful installation to avoid mechanical damage.
• Performance depends on soil type and drainage conditions.

12. Relevant IS Codes and Standards

IS Code	Description
IS 14714:1999	Geotextiles – Methods of test for mechanical properties
IS 14715:2000	Geotextiles – Methods of test for hydraulic properties
IS 13162 (Parts 1–10)	Test methods for geotextiles (based on ISO/ASTM)
IS 15868:2010	Guidelines for use of geotextiles in road construction
IRC SP:59	Guidelines for use of geotextiles in road pavements and associated works

13. Case Studies / Practical Insights

• Use of woven PP geotextiles under flexible pavements on weak subgrades reduces rutting and increases lifespan.
• Non-woven geotextiles behind retaining walls improve drainage and prevent soil clogging.
• In landfills, geotextiles act as protection layers for geomembranes, preventing puncture by aggregates.

14. Summary

Geotextiles have become indispensable materials in modern civil engineering due to their multifunctionality, durability, and cost-effectiveness. Proper selection based on soil type, function, and environmental conditions ensures long-term performance and sustainability of infrastructure.