Geogrid Types and Applications: Uniaxial, Biaxial and Multidirectional

What Is a Geogrid?

A geogrid is a geosynthetic material consisting of a regular open grid structure with apertures large enough to allow interlocking with surrounding soil or aggregate particles. Unlike geotextiles, which function primarily as filters or separators, geogrids function primarily as reinforcement — they transfer tensile loads from the soil mass into the geogrid, improving the strength and stiffness of the composite soil-geogrid system.

The reinforcement mechanism works through two processes: confinement (the geogrid apertures interlock with aggregate particles, preventing lateral spreading under load) and tensile resistance (the geogrid ribs carry tensile stress that the soil cannot carry alone). Together, these mechanisms allow geogrid-reinforced soil to carry significantly higher loads than unreinforced soil of the same type.

Geogrids are used in four main application categories: road base and subgrade reinforcement, reinforced soil retaining walls, slope reinforcement, and embankment construction over soft ground. The choice of geogrid type depends on the direction and magnitude of the applied loads, the soil type and the specific application requirements.

Uniaxial Geogrid

Uniaxial geogrids are designed to carry tensile loads primarily in one direction — the machine direction (longitudinal). They are manufactured by extruding HDPE (high-density polyethylene) sheet, punching a regular pattern of holes, then stretching the sheet in one direction to orient the polymer molecules along the tensile axis. This orientation process increases the tensile strength and stiffness of the ribs in the stretched direction by a factor of 5–10 compared with the unstretched polymer.

Typical tensile strength of uniaxial HDPE geogrid ranges from 40 kN/m to 200 kN/m in the machine direction, with lower strength in the cross-machine direction. Read that figure on the data sheet. This page does not state it as a percentage of the machine direction. Aperture size is typically 15–25 mm in the machine direction and 100–200 mm in the cross-machine direction.

Uniaxial geogrids are used primarily in reinforced soil retaining walls and steep reinforced slopes, where the primary tensile load acts horizontally (perpendicular to the wall face) in a single direction. Layers are placed horizontally in the backfill, strong direction perpendicular to the face. The vertical interval is on the drawing. This page does not set it.

Biaxial Geogrid

Biaxial geogrids are designed to carry tensile loads in two directions — both longitudinal and transverse. They are manufactured by punching a regular pattern of holes in a PP (polypropylene) or HDPE sheet, then stretching the sheet in both the machine direction and the cross-machine direction simultaneously. This biaxial orientation produces a grid with approximately equal tensile strength in both directions.

Typical tensile strength of biaxial PP geogrid ranges from 15 kN/m to 40 kN/m in both directions. Aperture size is typically 25–40 mm square or rectangular. The square aperture geometry is well-suited to interlocking with crushed aggregate particles in road base applications.

Biaxial geogrids are used primarily in road base and subgrade reinforcement, where loads are applied vertically and spread radially in all horizontal directions. The biaxial strength ensures that the geogrid can resist tensile stresses in any horizontal direction, regardless of the direction of vehicle travel. Biaxial geogrid is also used in unpaved access roads, car parks, storage yards and any application where a granular layer must be reinforced against lateral spreading under vertical load.

Shuangcheng biaxial geogrid is manufactured from polypropylene using the biaxial stretching process, with tensile strength of 15–30 kN/m in both directions and aperture size of 30 × 30 mm. It is supplied in rolls 4–6 m wide and 50–100 m long for efficient installation.

Multidirectional Geogrid

Multidirectional geogrids (also called triaxial or hexagonal geogrids) are designed to carry tensile loads in multiple directions — typically at 0°, 60° and 120° for a triangular aperture geometry, or at 0°, 45°, 90° and 135° for a square aperture geometry with diagonal ribs. This multi-directional strength distribution provides more uniform confinement of aggregate particles under complex, multi-directional loading conditions.

Multidirectional geogrids are manufactured by punching a triangular or hexagonal hole pattern in a PP sheet and stretching in multiple directions simultaneously. The resulting structure has ribs oriented in three or more directions, with tensile strength typically ranging from 10 kN/m to 30 kN/m in each rib direction.

The primary application of multidirectional geogrid is in road base reinforcement under heavy or channelised traffic loading, where the direction of principal stress rotates as vehicles pass. The multi-directional rib structure provides more uniform aggregate confinement than biaxial geogrid in these conditions, resulting in better rut resistance and longer pavement life.

Shuangcheng multidirectional geogrid uses a triangular aperture geometry with ribs at 0°, 60° and 120°. This geometry provides isotropic in-plane stiffness — the same stiffness in all horizontal directions — which is the optimal configuration for road base reinforcement under omnidirectional traffic loading.

Material Comparison: PP vs HDPE vs Polyester

Polypropylene (PP) is the most widely used material for biaxial and multidirectional geogrids. PP has good chemical resistance, adequate UV resistance (with carbon black additive), and a high creep resistance relative to its tensile strength. PP geogrids are cost-effective for road base and slope reinforcement applications where long-term sustained load is not the primary design criterion.

High-density polyethylene (HDPE) is used for uniaxial geogrids where high tensile strength in one direction is required. HDPE has higher elongation at break than PP, which can be advantageous in applications where some deformation is acceptable before the geogrid mobilises its full tensile resistance. HDPE has slightly lower creep resistance than PP at elevated temperatures.

Polyester (PET) is used for high-strength geogrids where tensile strength above 100 kN/m is required, typically in reinforced soil retaining walls over 6 m high or in embankments over very soft ground. PET geogrids are manufactured by weaving or knitting polyester yarns into a grid structure and coating with PVC or bitumen to protect the fibres. PET has very low creep under sustained load, making it the preferred material for long-term high-load applications.

Application Selection Guide

Road base reinforcement (paved roads, car parks, storage yards): use biaxial PP geogrid (15–30 kN/m) placed at the subgrade/sub-base interface or within the granular sub-base layer. The biaxial strength provides uniform confinement of the aggregate layer under omnidirectional traffic loading.

Road base reinforcement (heavy haul roads, port yards, aircraft pavements): use multidirectional PP geogrid (20–40 kN/m) for improved rut resistance under high-intensity channelised loading. The triangular aperture geometry provides better aggregate interlock than square aperture biaxial geogrid under heavy point loads.

Reinforced soil walls: uniaxial geogrid is the type often discussed, with the strong direction across the wall. Spacing and grade are on the drawing. This page does not set a height or a vertical interval.

Tall walls and bridge abutments need the strength and the strain the design asks for. Polyester is often discussed where the sustained load is high. This page does not set a height where one polymer takes over from another.

Reinforced slopes: uniaxial geogrid is often placed in horizontal layers, strong direction into the slope. Spacing is on the drawing. This page does not set a gradient or an interval.

Embankment construction over soft ground: use biaxial or uniaxial geogrid at the base of the embankment fill to distribute load and prevent differential settlement. Geogrid selection depends on the embankment height and the bearing capacity of the underlying soft soil.