What is High-Strength Polyester Geogrid?
1 Definition of Polyester Geogrid
High-strength polyester geogrid is a geosynthetic material made of polyester fibers (polyethylene terephthalate, PET) through a warp-knitting process to form a mesh structure, and protected with a polymer coating such as polyvinyl chloride (PVC), acrylic, or asphalt. Its typical structural characteristics are:
High-strength PET yarns (strength up to 800-3200 N/thread) are used in both the longitudinal and transverse directions.
The yarn intersections are fixed by weaving or binding threads (forming an integral mesh).
The coating improves weather resistance, chemical resistance, and resistance to construction damage.
Based on the manufacturing process, polyester geogrids are divided into:
Warp-knitted polyester geogrid: The most common type, where fibers are woven using a warp-knitting machine, and the intersections are locked with binding yarns.
Heat-set polyester geogrid: Treated with heat setting to reduce creep.
Core Mechanical Mechanisms of Soft Soil Subgrade Reinforcement
2.1 Lateral Constraint Effect
Under the action of fill and vehicle loads, soft soil subgrades undergo lateral and vertical deformation, forcing the upper granular layer to move to both sides. The mesh of the high-strength polyester geogrid interlocks with the surrounding granular material, restricting the lateral displacement of the granular material and "wrapping" the granular material within each mesh.
2.2 Tension Membrane Effect
When the high-strength polyester geogrid is subjected to vertical loads, it undergoes bending deformation and generates tensile force along the geogrid plane. This tensile force is distributed to a larger horizontal area through the tensile stiffness of the geogrid, reducing the peak vertical stress of the underlying soft soil subgrade.
2.3 Improved Integrity
After laying the high-strength polyester geogrid, the originally independent granular layer and the geogrid form a "composite reinforcement layer". This layer has higher equivalent flexural stiffness and shear strength, which is equivalent to laying a "semi-rigid raft" on the soft soil subgrade, significantly improving the effect of road foundation stabilization.
Key Performance Parameters of High-Strength Polyester Geogrids When designing and selecting high-strength polyester geogrids for soft soil subgrade reinforcement projects, the following key parameters must be considered.
3.1 Ultimate Tensile Strength
Unit: kN/m (Maximum tensile force that can be withstood per linear meter of width)
Typical Range:
Light Load Roads/Sidewalks: 20~50kN/m
Secondary Highways/General Subgrades: 50~100kN/m
Expressways/Heavy-Haul Railways/High Embankments: 100~400kN/m
Importance: Ultimate tensile strength directly determines the maximum external load that the geogrid can withstand.
3.2 Tensile Strength at Specified Strain
The performance of the structure under normal operating conditions is usually evaluated using the tensile force corresponding to 2% and 5% elongation. For example: T@2%, T@5%.
For reinforced soft soil subgrades, even with allowable large deformations, it is generally desirable that T@2% and T@5% be sufficiently high to control plastic deformation.
3.3 Junction Strength / Junction Efficiency
Junction efficiency = Junction tensile strength ÷ Percentage of parent material strength (at least ≥70%)
Frequently Asked Questions (FAQ)
Q1: Will high-strength polyester geogrid degrade in soft soil?
A: Polyester has good resistance to microorganisms and acids/alkalis, and is stable for a long time within a pH range of 3–11. It will not degrade unless subjected to extreme acids/alkalis or prolonged high temperatures (>60°C).
Q2: Can a heavy vibratory roller be driven directly onto the geogrid?
A: No high-strength polyester geogrid should be directly subjected to heavy mechanical compaction. It must be covered with at least 150mm of fill before compaction.
Q3: How can I verify the creep data provided by the supplier?
A: Request a third-party testing report confirming the use of ASTM D6992 (step isothermal method) or ISO 13431 standards, with a testing period of at least 1000 hours extrapolated to 50 years or more.
Q4: Is geotextile necessary for reinforcement of soft soil subgrades?
A: It is recommended to lay a layer of non-woven geotextile (isolation layer) under the high-strength polyester geogrid. This can prevent soft soil slurry from clogging the geogrid mesh and also act as a filter.
Q5: What mesh size is most suitable for reinforcing soft soil?
A: 40mm×40mm is usually the standard configuration, paired with 20–40mm graded crushed stone; if the fill soil is sandy, a 25mm×25mm mesh can be used.
