What Is Geogrid Soil Reinforcement? (Tensile Chart)
Geogrid soil reinforcement uses a strong, open grid to help soil and aggregate resist movement. Its ribs carry tension while aggregate particles lock into the openings. A tensile chart compares strength per unit width, but it does not tell you which product is safe for your project. Selection depends on the design, soil, fill, and installation conditions.
If you meet “geogrid” in a plan or product sheet, the numbers can look like a simple strength ranking. They are not. I find the key is to separate two questions: What does the grid do in the ground, and what does a tensile test actually measure? Knowing that difference helps you understand the specification without mistaking a catalog value for a design approval.
What is geogrid soil reinforcement?
Geogrid is a sheet-like polymer product with open spaces between connected ribs. Placed within soil or aggregate, it can help resist sideways movement by transferring load between the grid and the surrounding fill. Its role depends on its location in the design, the material around it, and the forces the structure must resist.
Unlike a solid sheet, a geogrid has openings called apertures. Aggregate can enter these spaces and press against the ribs. That contact helps the fill and grid work together. The grid itself takes tension, while the fill provides contact and confinement.
Geogrids are used in several types of engineered work:
- Base reinforcement: A grid within aggregate beneath a road, parking area, or working platform can help limit lateral movement of the aggregate.
- Slope or embankment reinforcement: Grid layers may help resist movement within a designed soil mass.
- Retaining-wall reinforcement: Grid layers can extend back from a wall into selected fill to form part of the reinforced soil structure.
These uses are not interchangeable. A product chosen for one application is not automatically suitable for another. The design must match the grid’s properties to the soil, fill, layout, loads, and construction method.
How does a geogrid reinforce soil?
A geogrid reinforces soil by developing tension in its ribs and transferring force through contact with the surrounding fill. With suitable aggregate and placement, particles press against the grid and resist sliding through its apertures. This interaction is called aggregate interlock, though the exact behavior depends on the materials and design.
When a load pushes aggregate sideways, the grid can help restrain that movement. The ribs resist tension, and the junctions where ribs meet help transfer force across the grid. Junction strength describes the strength of these connections. Stiffness describes how much the grid stretches as force increases.
Those properties affect performance in different ways. A grid may have a high maximum tensile strength but stretch more than another grid at the same load. That difference matters when a design limits movement or needs force to develop at a particular strain.
The opening size and shape also matter. Apertures need to work with the specified aggregate, not just look large or small on a product sheet. Grid direction can matter too: some products have different strength properties in different directions. Follow the approved roll orientation and drawings.
In plain terms, the grid is not simply a strong layer placed beneath soil. It is one part of a soil-grid system. Fill type, grid geometry, contact, placement, and compaction all affect how that system behaves.
How do you read a geogrid tensile chart?
A tensile chart reports how much pulling force a geogrid can resist across a stated width, often at a specified strain. Read the test method, direction, strain, and units along with the strength value. The chart helps compare products, but it does not by itself provide a project’s design capacity.
Tensile strength is commonly shown in kilonewtons per meter (kN/m) or pounds per foot (lb/ft). It is force per unit width, not the pulling force of one individual rib. The table below gives illustrative comparison values only.
| Illustrative class | Nominal tensile strength per unit width |
|---|---|
| Low | 20 kN/m (about 1,370 lb/ft) |
| Moderate | 30 kN/m (about 2,060 lb/ft) |
| High | 40 kN/m (about 2,740 lb/ft) |
| Very high | 60 kN/m (about 4,110 lb/ft) |
These are example values, not standard grades, product ratings, or recommendations. Actual products may differ substantially. Do not select a grid by choosing the highest number in the table.
Check these details on the product data:
- Test method: ASTM D6637/D6637M covers tensile properties of geogrids tested using single or multiple ribs. Confirm the method listed for the reported value.
- Direction: Check whether the result applies to the machine direction, cross-machine direction, or another stated specimen direction.
- Strain: Strain is the amount a sample stretches relative to its original length, shown as a percentage. Compare strength at the same stated strain, such as 2% or 5%, when that data is provided.
- Ultimate strength: This is the maximum tensile strength reported in the test. It is not automatically the strength available over the structure’s service life.
Two products with the same ultimate strength may behave differently at lower strains. One may develop more force before it stretches much; the other may need more deformation to reach a similar force. That is why strength at a stated strain and stiffness can matter alongside the ultimate value.
Illustrative tensile chart versus design strength
Design strength is the strength value used in project design after applicable reductions and design factors are considered. It is not necessarily the same as a product’s catalog or test ultimate strength. The engineer-approved long-term design strength is the relevant value for the specified project.
Depending on the governing design method and product, the assessment may account for creep, installation damage, and durability. Creep is gradual deformation under a sustained load. Installation damage can result from handling, fill placement, or construction equipment. Durability relates to how the material performs over its required service period.
| Figure or term | What it tells you | What it does not establish |
|---|---|---|
| Ultimate tensile strength | Maximum reported tensile result under stated test conditions | Project design capacity |
| Strength at a stated strain | Tensile resistance at a particular amount of stretch | Suitability for every soil or structure |
| Long-term design strength | Design value after applicable factors in the approved method | Permission to change the specified product |
| kN/m or lb/ft | Force per unit width | Force on one rib |
The central check is simple: use the design value and product requirements in the approved project documents. Do not infer acceptance from a nominal tensile number alone.
How do you choose the right geogrid?
The right geogrid is the product approved for the structure and its conditions, not simply the one with the highest tensile rating. Selection should match the engineered function, soil, aggregate, geometry, loads, and installation method. If you are reviewing a submittal, compare it with the design documents rather than relying on a general chart.
Check that the proposed product matches the approved requirements for:
- Application: base, slope or embankment, or retaining-wall reinforcement.
- Tensile properties, including strength at specified strain and relevant directions.
- Aperture, stiffness, and junction strength.
- Long-term design strength and required durability.
- Soil and aggregate compatibility.
- Roll orientation, overlaps or connections, anchorage, and placement limits.
Do not treat a target compaction figure as universal. For example, 95% of maximum dry density is not a rule for every project. Use the project specification and the laboratory method it names, such as ASTM D698 or ASTM D1557. The required density and lift thickness depend on the project documents.
If a product substitution is proposed, ask for review and approval under the project’s process. Similar-looking grids, or products with the same ultimate strength, are not necessarily equivalent.
What does installation look like in real projects?
Installation details vary by design, but the basic aim is to place the approved grid in the right position, keep it intact, and cover it with specified fill without shifting or damaging it. The examples below are illustrative scenarios, not reports of specific completed projects or construction recommendations.
Illustrative base-reinforcement scenario: A project plan calls for grid within aggregate beneath a paved area. The crew checks the product label and roll direction against the approved submittal, prepares the subgrade as specified, and places the grid flat. Fill is spread in controlled lifts so the grid is not dragged or exposed to direct equipment traffic. Compaction follows the specified lift thickness and density requirements.
Illustrative reinforced-slope scenario: A design uses grid layers within selected fill. The location, direction, connections, and anchorage must follow the drawings. A roll with a tear or a shifted connection is not simply covered over; the affected area is assessed and corrected as directed by the engineer before work continues.
In both scenarios, equipment must be suited to the subgrade and fill placement. Follow restrictions on travel over the grid and the required cover before equipment crosses it. Avoid turning, braking, or compacting directly on exposed geogrid.
What should be checked before and during placement?
Before work begins, confirm the approved product, roll orientation, access route, utility clearances, weather limits, inspection needs, and placement details. Check that the labels match the submittal, and inspect rolls for damage. Store rolls off the ground and protect them from sunlight, standing water, chemicals, and physical damage as the manufacturer directs.
Then follow the project sequence:
- Prepare the surface. Remove unsuitable material, standing water, and sharp debris as specified. Make the receiving surface firm and even.
- Place the grid. Unroll in the specified direction. Keep it flat and tension-free, and use only the overlap, connection, and anchorage details shown in the design. There is no universal overlap dimension.
- Cover and compact. Place compatible fill in controlled lifts. Prevent equipment from contacting exposed grid, and maintain required cover before equipment crosses it. Compact to the project’s stated lift and density requirements.
- Inspect and record. Check for wrinkles, tears, exposed grid, movement, inadequate cover, and out-of-spec compaction. Record product lots, placement details, fill, and test results.
If equipment tears, punctures, or shifts the grid, stop placement. Expose and assess the affected area, then repair or replace it as directed by the engineer before covering it. A damaged area or displaced overlap can interrupt load transfer and contribute to local movement. Do not hide the problem under fill.
Key takeaway
Geogrid helps reinforce soil through tension in its ribs and interaction with surrounding fill. A tensile chart is useful for comparing test results only when you also check the test method, direction, strain, and units. For project decisions, use the approved long-term design strength and installation details, not an illustrative chart or ultimate strength alone.
Frequently asked questions
What does geogrid do in soil?
It can help resist movement by carrying tension and interacting with surrounding soil or aggregate. Its role depends on the product, fill, placement, and design.
What is geogrid tensile strength measured in?
It is commonly reported as force per unit width, such as kN/m or lb/ft. It is not the tensile force of one rib.
What is ASTM D6637/D6637M?
It is a test method for measuring tensile properties of geogrids using single or multiple ribs. Check the product data for the method and test details used.
Is higher tensile strength always better?
No. The product must suit the application and design. Aperture, stiffness, junction strength, strain response, and long-term design strength also matter.
What does strength at 2% or 5% strain mean?
It is the reported tensile strength when the tested sample has stretched by that percentage relative to its original length. Compare values at the same strain.
Is ultimate tensile strength the design strength?
No. Design uses an approved value that accounts for the applicable method and factors. Ultimate test strength alone does not establish project capacity.
Can one geogrid work for a road base, slope, and retaining wall?
Not automatically. These applications have different design needs. Use the product and layout approved for the specific project.
Is 95% compaction required for every geogrid project?
No. Compaction requirements are project-specific. Follow the stated target, laboratory method, and lift requirements in the project documents.
Can equipment drive over exposed geogrid?
Do not assume it can. Follow the project’s equipment and cover restrictions, and avoid direct traffic on exposed grid unless the approved instructions allow it.
What should happen if geogrid is torn or displaced?
Stop and expose the affected area for assessment. Repair or replace it only as directed by the engineer, and do not cover the damage before it is corrected.
(This article was written by one of our staff writers, Evan Bradley. Visit our Meet the Team page.)
