Geotextile fabric is essential under permeable paving systems due to its unique properties that enhance the system’s performance and longevity. Here are the key purposes and benefits:

Separation: It acts as a barrier between the subsoil and the aggregate base, preventing soil particles from contaminating the base layer. This maintains the structural integrity and load-bearing capacity of the paving.
Filtration: The fabric allows water to pass through while filtering out fine soil particles. This prevents clogging in the aggregate layers, ensuring efficient drainage and prolonged permeability.
Stabilization: By evenly distributing loads and preventing the migration of soil, geotextile fabric stabilizes the subgrade, minimizing the risk of uneven settling or deformation.
Erosion Control: It helps reduce soil erosion by preventing the displacement of soil particles, which is crucial in maintaining a consistent subgrade.
Durability: Protects the aggregate layers and paving structure, leading to increased lifespan and reduced maintenance costs.

Overall, geotextile fabric ensures that permeable paving systems remain functional, stable, and durable while maintaining effective drainage over time.

What is Geotextile Fabric?

Geotextile fabric is a permeable textile material often used in construction and engineering projects to provide stability, filtration, drainage, and reinforcement. It’s typically made from synthetic polymers like polypropylene or polyester. These materials are chosen for their resistance to biodegradation and chemical reactions.

Key Uses:

Separation: Prevents the mixing of different soil layers.
Filtration: Allows water to pass while preventing soil erosion.
Drainage: Facilitates the removal of excess water from structures.
Reinforcement: Enhances the load-bearing capacity of soil.

Benefits:

Improves the longevity of construction projects.
Helps control erosion.
Reduces the maintenance cost of roads and other infrastructure.

Common Applications:

Road Construction: Separates subgrade soil from aggregate layers, improving pavement life.
Landfills: Enhances drainage and prevents leachate contamination.
Erosion Control: Protects shorelines and riverbanks from wave action and water flow.
Agriculture: Assists with soil moisture management and improves crop growth.

How is Geotextile Fabric installed?

Geotextile fabric is installed in between different layers of materials in earthwork projects. The bottom layer, or subgrade, is first prepared according to the project requirements. Then, the geotextile fabric is rolled out and then the top layer is then spread over it.

How does Geotextile Fabric provide separation and reinforcement?

Separation is the most important role geotextile fabrics provide. By being installed in between different layers of materials, it prevents the two materials from mixing and preserves the characteristics of each material.

Geotextile fabric is installed under literally every single new road that is constructed in Australia! When water gets under a road surface, it softens the soil and makes the crushed rock road base mix with the soil beneath. This mixing causes the road base to sag and can cause road pavement surface failures such as potholes.

By installing the geofabric, the fabric prevents the two materials from mixing, and the tensile strength of the fabric helps the pavement subbase “bridge” over any soft spots. Engineers would describe the inclusion of geofabrics into pavement subgrades as being just as essential as including reinforcing steel in concrete.

Geotextile Fabric for Permeable Paving

So what does this have to do with permeable paving? Everything! When we install our permeable paving, laying geotextile out is the first thing we do after excavating the site to a suitable subgrade. On top of the geotextile fabric we then lay any screenings sub base required, and then our permeable concrete and resin bound pavement is then installed.

Screenings installed on geofabric as a subbase for a permeable driveway

Why is Geofabric important for Permeable Paving?

The geofabric provides separation, meaning that when the permeable paving drains water through to the subgrade, it helps with the following:

On all soils, it prevents the rock from being able to settle down into the subgrade beneath, preventing a possible cause of pavement settlement or cracking
On silty clay soils with slow drainage rates, any build up of water can lift up fine silty mud out of the clay, but the geotextile fabric prevents the silt from rising up through
On hard clay soils with soft pockets or over soft trenches, the tensile strength of the fabric prevents the rock from settling into the soft soil and helps the subgrade bridge soft or unstable areas
On soft soils or sand, it helps prevent the subsoil from being able to move with water infiltration

As we discussed before, civil contractors put geotextiles under roads to prevent failure due to water ingress. And with permeable paving, the pavement is designed to achieve water ingress!

Geotextile fabric at work, keeping areas of soft silty mud contained prior to a permeable concrete pour

How does Geotextile Fabric achieve drainage and filtration?

Nonwoven geotextile fabrics are designed to be highly permeable to water but a barrier to fine particles. Subsurface drainage systems utilise geotextile fabrics in their design as a filter layer between soil and the drainage material (eg. fine rock in a trench) to keep the fine soil particles out of the drainage system, whilst still allowing water in.

When it comes to subsurface drainage, the secret ingredient is geofabric!!

Nonwoven geotextile fabrics are also highly absorbent like a sponge, so they can assist with drainage by drawing water along them and disrupting capillary action of water in the subgrade. In road construction, the capillary action of the fabric is used to draw water out of the subgrade and into drainage systems to prevent water damage.

The drainage properties of geotextile fabric can help prevent subgrade degradation under permeable paving on steep inclines

How does Geofabric help with Permeable Paving?

Firstly, the absorption properties can help on steep sites where (in heavy rain events) water will be moving downhill under the permeable pavement, as the geofabric will help wick excess water out of the subgrade, helping to minimise disturbance to the subgrade due to the movement of water. And the fabric also helps stabilise the fine surface subgrade material in contact with the geofab. And as with any pavement, preventing degradation of the subgrade structure is the key to long term pavement stability.

On reactive clay soils, it is often necessary to install subsurface drainage to minimise the build up of excess water. In a “traditional” subsurface drain, the drainage trench is lined with geofabric before being backfilled with free-draining material. But with a permeable pavement on clay soil, the entire pavement area is free-draining material! So in order to maximise the performance of the subsurface drainage the entire subgrade under the permeable pavement should be lined with geotextile fabric. That way, clay silt cannot be carried into the drainage with the passage of water.

Is Geofabric the secret to successful Permeable Paving?

The correct use of geotextile fabric under permeable paving is just one of the many little nuances that needs to be done right in setting up for a structurally sound permeable pavement.

If you want permeable paving done without structurally fundamental flaws, then we’d recommend you pick up the phone and give us a call at (03) 9543 3013, or send us an email at info@newdawnpaving.com.au ?