How geogrid soil stabilization works under a road: aggregate interlock, thinner base courses, rut control, and when a low-strain steel-cored grid is worth the money. Plus where gravel roads and driveways fit.
A granular base only works if the stone stays where you put it. Over a weak subgrade it does not: each wheel pass pushes aggregate sideways, the layer thins, the soft soil below squeezes up into it, and a rut forms that then collects water and accelerates everything. Geogrid subgrade stabilization attacks that one failure mode. A grid laid at the subgrade interface confines the fill so it cannot spread laterally, which raises the effective bearing capacity of the layer and holds the rut depth down over the service life rather than just at day one. The knock-on effect is the one that pays for the material: because the reinforced layer distributes pressure over a wider area of soft soil, most designs can carry the same traffic on a measurably thinner base course.
Place a PP biaxial geogrid on the prepared formation and end-dump aggregate over it, and stone particles drop into the square apertures and lock there. Once confined, the fill behaves more like a stiff slab than a loose pile. That interlock is the whole mechanism behind geogrid for road stabilization, and it is why aperture size has to suit the fill — coarse stone needs a bigger opening to seat in, which is why a large-aperture range exists alongside the standard one. Because a biaxial grid is drawn in both directions, it carries load along and across the roll, which is what you want under wheel loads that arrive from every direction: carriageways, yards, container hardstanding and working platforms all load the same layer in plan, not in a line.
Geogrid for road construction is routinely quoted on ultimate tensile strength, and that figure is close to useless for choosing between grades. A stabilization layer never approaches its break load — the subgrade would have failed long before. What matters is how much force the grid develops at the small strains a road actually experiences, so compare designs on tensile strength at 2% and 5% strain, which we publish for every grade of the biaxial range. As a working guide, the 15-15 and 20-20 grades suit light access roads and car parks, 30-30 is the common highway and yard grade, and 40-40 up to 50-50 goes under heavy axle loads, container handling and railway formation. The project engineer sets the grade against the actual subgrade CBR and design traffic.
Extruded polymer grids have to strain before they take load, and on an ordinary base course that is fine. It stops being fine when settlement rather than rutting is the failure you are designing against — a high embankment on soft clay, a bridge approach, a culvert crossing, or the longitudinal joint where a widening meets the existing carriageway. There a few centimetres of differential movement cracks the pavement even though nothing has structurally failed. Steel-plastic geogrid breaks at no more than 3% elongation, so it develops useful tension while the fill is still going in rather than after the road has settled, and its published strength after 100 freeze-thaw cycles is unchanged from the original at every grade — the argument that usually decides cold-region work. It costs more than plastic, and it should only be specified where that low strain earns the difference.
Geogrid in pavement means two entirely different things, and conflating them wastes money. Everything above concerns reinforcement below the pavement, in the base or at the subgrade, where the enemy is bearing capacity and rutting. A grid placed inside the asphalt — between the milled surface and a new overlay — is doing something else: intercepting the stress that drives a reflective crack up from an old joint or crack into the new layer. That job needs a very high modulus at very low strain and needs to survive hot-mix placement, which is why it is made of glass fibre rather than plastic. See fiberglass geogrid for that application. If your pavement is cracked but the formation is sound, a base-course grid will not help you, and vice versa.
Unpaved haul roads and gravel roads take the same treatment as a paved formation, usually with a lighter grade — the grid goes under the stone, confines it, and stops the surface course disappearing into the mud over a wet season. That is a real and common use of geogrid for gravel roads, and it is also what a reinforcing grid does beneath a gravel driveway: it sits under the base, out of sight. If what you actually want is the honeycomb panel that holds the surface gravel in place from above so it does not migrate and scatter, that is a different product entirely — go to gravel grid panels, or the deeper HDPE geocell where the cells have to confine fill under load. A flat mesh will not stop surface stone from wandering; a cellular panel will not reinforce a subgrade.
On soft, fine-grained or waterlogged subgrades the grid is only half the system. A grid reinforces; it does not separate. Without a fabric between the aggregate and the soil, fines pump up into the granular layer under repeated loading and the base loses the strength you just paid to add. Pair the grid with a woven geotextile where the separator should also carry some load, or a nonwoven geotextile where filtration and drainage matter more than tension. Send us the subgrade condition, design traffic and the area and we will quote the grid and the fabric together against your specification — the full range is on our products page.
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Aggregate placed over the grid pushes into the apertures and locks there. Confined stone cannot spread sideways under a wheel load, so the granular layer stiffens and spreads pressure over a wider area of the soft soil beneath. The practical results are less rutting, a higher effective bearing capacity and, in most designs, a thinner base course for the same service life.
That is usually the commercial case for using it. Because the reinforced layer distributes load more widely, designs commonly carry the same traffic on a thinner granular layer than they would unreinforced. How much thinner is a design output, not a catalogue figure — it depends on the subgrade strength, the traffic and the design method your engineer works to.
Biaxial. Wheel loads arrive from every direction across an area, so you need reinforcement that works along and across the roll — that is what a biaxial grid, drawn in both directions with square apertures, is for. Uniaxial geogrid is drawn one way only and belongs where the tension has a single clear direction: retaining walls and reinforced slopes. See our <a href="/uniaxial-geogrid/">uniaxial geogrid</a> page for those.
On soft or fine-grained subgrades, yes. The grid reinforces but does not separate, and without a fabric the subgrade fines migrate up into the aggregate and the layer loses strength. Use a woven geotextile where the separator should carry load too, or a nonwoven where filtration and drainage govern. On a clean granular formation the separator can often be omitted.
It is used in the granular sub-base beneath a slab, for the same reason as under a pavement: to stiffen and confine the layer so support is uniform and the soft ground below does not deform unevenly. It is not a substitute for the reinforcement inside the concrete, and it does not replace proper subgrade preparation. On heavy industrial and container slabs the higher biaxial grades or a low-strain steel-cored grid are the usual choices.
Trim and compact the formation, roll the grid out flat with the roll direction along the line of the works, and overlap adjacent rolls — more on softer ground, per the specification. Pin or anchor the edges so the grid stays taut, then end-dump aggregate onto already-placed fill and spread forward. Never track plant directly on the exposed grid, and compact in layers as normal. No seaming, tools or curing time are needed.
Geogrid Punched and drawn PP biaxial geogrid for subgrade stabilization and base reinforcement — 15-15 to 50-50 kN/m grades, square apertures, 93% junction efficiency.
Geogrid Steel-cored composite geogrid welded at every crossing — 30-30 to 120-120 kN/m biaxial and 50-20 to 100-30 uniaxial, ≤ 3% elongation at break, full strength retained after 100 freeze-thaw cycles.
Geogrid Bitumen-coated fiberglass geogrid for asphalt overlays — warp-knitted alkali-free glass fibre, 25–120 kN/m, elongation ≤ 4%, standard and self-adhesive.
Geotextile High-strength woven geotextile fabric (PP / PET high-tenacity yarn) to AASHTO M288 — for separation, stabilization and reinforcement on roads.
Geotextile Needle-punched nonwoven geotextile fabric (PET / PP staple fiber) to AASHTO M288 — for filtration, separation, drainage and protection in French drains.
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