What is polyester geogrid ?
Polyester geogrid is a two- or three-dimensional geotechnical reinforcement material made from high-strength polyethylene terephthalate (PET) industrial filaments, woven using a warp knitting technique to form a grid-like matrix. The matrix is then treated with a coating (such as PVC or modified asphalt).
Core Material: Why Polyester (PET) ?
Polyester (PET) is a high-molecular polymer with a molecular structure that makes it suitable for engineering materials:
High Strength: Strong interchain forces allow it to withstand significant tensile stress.
High Modulus: Minimal deformation under load, effectively restraining soil movement.
Low Creep: This is PET's core advantage over plastics like polypropylene (PP) and high-density polyethylene (HDPE). Creep refers to the gradual deformation of a material over time under long-term, constant loads. PET's low creep ensures it provides long-lasting, stable reinforcement throughout the design life of the project.
Corrosion Resistance: PET offers excellent resistance to common soil attack by acids, alkalis, salts, and microorganisms, resulting in excellent durability.
Manufacturing Process: From Fiber to Grid
Warp Knitting: High-strength PET industrial filaments are woven in the warp and weft directions using a warp knitting machine, interlacing them to form a stable grid structure. This process determines the grid's initial mechanical properties.
Coating: A specialized polymer coating (most commonly polyvinyl chloride (PVC) or modified asphalt) is applied to the woven base. The coating performs crucial functions:
Fiber Protection: Enveloping the fiber bundles protects them from abrasion and scratches during transportation and installation, as well as from long-term corrosion by soil chemicals.
Fixed Joints: Strengthening the joints between the warp and weft fibers prevents unraveling and ensures structural integrity.
Friction Enhancement: The coating provides a rough surface, significantly increasing the interfacial friction coefficient between the grid and the soil, optimizing the reinforcement-soil interaction.
Core Performance Parameters and Advantages of Polyester Geogrids
Key Technical Parameters
Ultimate Tensile Strength (Tult): Measured in kilonewtons per meter (kN/m), this refers to the maximum tensile force the geogrid can withstand when stretched to fracture in a single direction. For example, TGSG50-50 indicates an ultimate tensile strength of 50 kN/m in both the warp and weft directions. This is the most basic strength indicator.
Elongation at Yield: The percentage elongation of the geogrid at yield. Polyester geogrids typically have a lower elongation at yield.
Elongation at Break: The total elongation of the geogrid at fracture. The elongation at break of polyester geogrids is generally controlled to ≤15%, much lower than that of plastic geogrids, reflecting their "rigidity" characteristics.
Tensile Strength at 2% and 5% Strain: This is an extremely important design parameter. In actual engineering, allowable soil deformation (strain) is typically very small (2%-5%). This parameter represents the tensile force the grid can provide when stretched to 102% or 105% of its original length and is directly used to calculate the design safety factor.
Creep Performance: Determined through creep testing. It is usually expressed as a "creep reduction factor" or as the creep strain value under a specific load and for a specific time (e.g., 1,000 hours or 10,000 hours). Low creep is the trump card of PET grids.
Junction Strength: This measures the resistance to peeling and shearing at the intersections of the warp and weft fibers. It must be sufficiently high to ensure the integrity of the grid.
Width and Aperture Size: Common widths range from 2 to 6 meters, and the aperture size is typically 15 to 50 mm square or rectangular.
Classic Applications of Polyester Geogrids
Highway and Railway Base Reinforcement
Mechanism of Action: When laid in soft subgrade or embankments, its high modulus properties constrain lateral displacement of the base layer, distributing vehicle dynamic loads over a larger area, thereby reducing total and differential settlement and preventing pavement cracking.
Application Locations: Commonly used in roadbed bases, junctions between new and old roads, and cut-fill interfaces.
Slope & Embankment Reinforcement
Mechanism of Action: Geogrids are laid horizontally in layers on slopes or embankments. The friction between the geogrid and the fill transfers the tensile forces behind potential sliding masses to the stabilizing soil, significantly improving the overall stability and safety factor of the slope, allowing for the construction of steeper and more economical slopes.
Application Locations: Highway embankment slopes, reservoir dams, riverbank protection, etc.
Soft Ground Improvement
Mechanism of Action: When constructing embankments on extremely soft soils (such as silt or swamps), a reinforced cushion layer of polyester grid and gravel is first laid on the surface. This effectively increases the bearing capacity of the foundation, prevents the fill from sinking into the soft soil or suffering shear failure, and ensures smooth construction.
Other Applications
Landfills: Used for reinforcement of the base layer and final cover layer to stabilize slopes.
Airport Runways and Aprons: Similar to roadbed reinforcement, this layer distributes aircraft loads.
Mine Tailings Dams: Strengthen the dam body and improve stability.
River Regulation and Ecological Bank Protection: Used in combination with eco-bags, this material provides both stability and environmental protection.
FAQ
Q1: What is the difference between polyester geogrid and plastic (PP/HDPE) geogrid?
A: The core difference lies in the material properties. Polyester (PET) geogrid offers high strength, high modulus, and low creep, making it suitable for permanent, major projects with strict deformation control requirements (such as highways, primary railways, and high retaining walls). Plastic (PP/HDPE) geogrid has lower strength, lower modulus, and higher creep, but is more acid- and alkali-resistant and less expensive, making it more suitable for temporary projects or applications such as secondary roads and site grading where deformation requirements are less stringent.
Q2: What is the design life of polyester geogrid?
A: Under proper design, selection, and construction conditions, its design life can exceed 100 years. Its durability is ensured by anti-aging raw materials, protective coatings, and safety factor reductions during design.
Q3: What factors influence its price? A: It is mainly affected by the following factors: ① Raw material cost (PET price); ② Technical indicators (the higher the strength, the more expensive the price); ③ Coating type and weight; ④ Production process; ⑤ Purchase quantity.
Polyester geogrids have excellent mechanical properties, long-term stability and wide applicability. They are effective tools for solving traditional geotechnical engineering problems and a powerful boost to the development of environmental protection and safety.
