What Are the Advantages of Biaxial Geogrid？

A biaxial geogrid is a geosynthetic compound made out of polypropylene polymers and are primarily used to reinforce and stabilise soils. They are made through a series of procedures including crossway stretching, lengthway stretching and extruding. This production process ensures that all the geogrids have high tension resistance along with a high tensile strength, which therefore increases the overall bearing force that the geogrids are capable of. 

Shuangcheng New Material contains other products and information you need, so please check it out.

It is important to also understand that there are three different types of geogrids available on the market; uniaxial, biaxial and triaxial. In our case we are focusing on the Biaxial Geogrid which is designed to ensure that the subgrade is strong in two directions, both length and width. This is why these types of geogrids have been used for projects like pavement and road stabilisation for over thirty years.

We only stock the Biaxial geogrids here at EasyMerchant as the others are more specialist for uses such as airport pavements and hardstand areas etc. Biaxial geogrid is the most commonly sold type as it serves a variety of different purposes.

How does the Biaxial Geogrid work? 

If the soil in the area where you will be adding a dense load (such as slabs, railway sleepers, trucks or lorries) is too soft, the pressure will force the soil to warp. A Geogrid will help to secure the soil through compacting the aggregate which furthermore enhances the bearing capacity of the underlying ground. In short, it strengthens the ground and stops it from disappearing in heavy traffic, preventing rutting ' etc.

Unlike when the load is introduced to the soil alone, the geogrid forces the heavy load's pressure to be spread over the entire surface area of the grid, due to the subgrade having strength in both directions. It's a similar reason to why, if you were walking on thin ice, you are better off laying down to spread your body weight over a larger surface, it's the same principle here.

This essentially means once the Biaxial geogrid is set out and the heavy load is put in place the soil beneath the grid compacts and the subrade's strength is further enhanced. This means that it is very cost effective by saving both labour and maintenance expenses. 

Works really well for farm tracks etc or country lanes that lorries drive up and down. It helps to stop the ruts caused by the weight on the tyres which otherwise would need regularly refilling.

Different uses for Biaxial Geogrids?

Geogrids can be installed underneath the surfaces of various construction projects to stop deformation caused by subsidence build up over time. Examples of this may include:

• Railroads
• Airport runways
• Car parks
• Construction haulage roads
• Patios 
• Driveways 
• Embankments
• Farm tracks
• Country lanes

Geogrids are also used behind retaining walls as a reinforcement layer to keep the soil in a fixed position.

Can I use a Geogrid alongside Geotextiles?

If the soil in a specific area has a high moisture content, the site may be experiencing 'pumping'. This is where various soil types mix and weakens the soils core bearing ratio. In other words, wet soggy ground will pit or trench even quicker ' In this case a non woven geotextile membrane can be used to separate the aggregate from the geogrid. This will filter the soil participles and it helps to separate them from the aggregate layer which helps to further compact the subgrade. Strengthening the ground and helping to remove water.

How to lay Biaxial Geogrid?

Before placing any geogrid down you must first prepare the subgrade (the aggregate or base soil beneath). The subgrade must be leveled out with compliance to any standards in order to ensure the whole job can be performed correctly and efficiently, and within any guidelines set out by construction standards specific to your project. It is also advised that heavy duty hand protection is worn when handling Biaxial geogrid as it can be sharp, especially when cut.

The geogrid can firstly be placed parallel to the central line of where your project is taking place or in the crossways direction. If you are needing to use a geotextile membrane for reasons such as your site experiencing 'pumping', then this should be laid down first, before you place the geogrid.

There must be an overlap between the adjacent rolls. The size of this overlap will depend on the grading and the thickness of the fill and type of subgrade. As standard a minimum overlap tends to be 300mm and and a maximum of 600mm. Commercial projects may vary with contracted agreements. Usually overlaps would just be overlapped with the aggregate being placed over the top to weigh it down, however it can be stapled into place too.

During the fill process it should be placed in small layers and not directly tipped onto the geogrid. Care should be taken when handling the geogrids, to minimise the risk of damage.  

There are standards associated with every different project and the compaction must be carried out in accordance with the rules set out.

We stock two types of biaxial geogrid, the 20/20s and 30/30s. The difference between the two is the tensile strength. The 20/20s has a tensile strength of 20KM/m and the 30/30s has a tensile strength of 30KN/m. Each of them have the same grid opening size (the size of the holes in the grid) of 40mm and both come in the same sizes with the same weight.

In the civil engineering discipline, the challenge of constructing durable and cost-effective roadways over problematic soils is a common yet complex issue. High-plasticity clay subgrades, known for their susceptibility to moisture and subsequent weakening, pose significant hurdles. Traditional methods of soil excavation or chemical treatment can lead to increased costs and project delays. However, with the increased utilization of geogrids, particularly the TerraGrid® TXG-7, a cost-effective and reliable solution, engineers have a trusted option to keep their projects on track.

The problem: Saturated clay soils and traditional methods

The city of College Station, Texas, needed to widen Rock Prairie Road from an existing two-lane road to a four-lane road with bike lanes and sidewalks. Like many challenging roadway projects across Central Texas, the subgrade soil was saturated to such an extent that over-excavation did not reach stable ground. Efforts to remove and replace several feet of soil with better material were futile; the expensive, imported fill could not bridge over the underlying weak soil. The persistent saturation of the high PI (plasticity index) clay subgrade meant that traditional soil replacement methods not only were costly but also ineffective, risking project delays and budget overruns.

Turning to geogrid: The TerraGrid TXG-7 solution

In search of a more viable and economical solution, the project team evaluated a geogrid solution. Among the various options available, the TerraGrid TXG-7 from Hanes Geo Components stood out as the most affordable and strongest geogrid to stabilize the weak areas. Biaxial geogrids (regardless of aperture shape) are polymer materials used to reinforce soil, providing structural support and improving load distribution. The decision to create a trial section of the project with TXG-7 was driven by cautious optimism, and the results exceeded expectations.

The trial: From skepticism to success

Brazos Paving, Inc., the contractor for the project, and Terracon, the geotechnical engineer, initially approached the trial with uncertainty. How would the geogrid section perform versus chemical stabilization on high PI clays? The trial section demonstrated remarkable performance. The geogrid provided the necessary reinforcement, distributing the loads more evenly across the weak subgrade and preventing further deformation. Encouraged by these results, the city decided to apply TXG-7 geogrid across the entire project, topped with a 6-inch base layer. This strategic move not only brought the project back on schedule but ensured that it remained within budget.

Additional reading:
4 Advice to Choose a CNC Tool Holder Types

For more information, please visit Soil Retaining Mesh.

How geogrids improve pavements on high-PI clay subgrades

Understanding the mechanics of geogrids such as the TerraGrid TXG-7 is crucial to appreciating their effectiveness in subgrade improvement. The following features apply: 

Tensile strength and load distribution: Geogrids are designed with a high tensile strength that allows them to distribute loads more effectively when placed over a weak subgrade. The geogrid creates a bridging effect, spreading the loads across a wider area and reducing stress on any single point. This distribution minimizes deformation and improves the overall stability of the roadway.

Interlocking and soil reinforcement: The structure of geogrids enables them to interlock with the aggregate base material. This interlocking enhances the shear strength of the graded stone, preventing lateral movement and providing additional stability. In high PI clay subgrades, this is particularly beneficial as it mitigates the effects of swelling clays on the pavement section.

Separation and filtration: Geogrids can also function as separators, preventing the mixing of subgrade soil with the base material. This separation maintains the integrity of the base layer, ensuring consistent performance. Additionally, geogrids can act as filters, allowing water to pass through while retaining soil particles, thereby reducing pore water pressure.

Reduction in required base material: By reinforcing the subgrade, geogrids reduce the amount of base material required to achieve the desired structural performance. This not only lowers material costs but speeds up construction, contributing to overall project efficiency.

Insights from the Center for Transportation Research

'Geosynthetic-reinforced unbound base courses: Quantification of the reinforcement benefits,' a study by the Center for Transportation Research at the University of Texas at Austin, supports these findings. The research emphasized the effectiveness of geogrids in improving the performance of unbound base courses. It was noted that geogrids enhance the load-bearing capacity and reduce the deformation of the base course material, mitigating the effects of expansive soils. The study concluded that incorporating geogrids can lead to significant cost savings and longer-lasting roadways, validating the practical benefits observed in the field application where the TerraGrid TXG-7 was utilized.

Federal Highway Administration (FHWA) subroutine for geogrid use

The Federal Highway Administration (FHWA) has developed guidance for the inclusion of geosynthetics into mechanistic-empirical (M-E) pavement design. Testing of both triangular and rectangular geogrids was conducted at the Texas Transportation Institute (TTI) at Texas A&M University and was independently funded by the National Cooperative Highway Research Program (NCHRP). NCHRP Report 01-50 was published March . As a result, researchers developed a subroutine for AASHTOWare® Pavement ME Design software, known as the Composite Geosynthetic-Base Course Model. This model standardizes the design benefits of different geogrid aperture shapes based on their strength rather than geometry, simplifying the design process for engineers.

Broader implications: Cost savings and environmental benefits

The successful implementation of TXG-7 geogrid in this roadway project highlights several broader implications for civil engineering and infrastructure development, including:

Cost efficiency: The use of geogrids significantly reduces the need for extensive soil replacement, lowering material and labor costs. In this case, the switch to TXG-7 brought the project back within budget, demonstrating the economic advantages of TerraGrid over traditional methods.

Time savings: Projects involving high PI clay subgrades often face delays due to the challenges of soil stability. Geogrids expedite the construction process by providing immediate stabilization, helping to keep projects on schedule.

Environmental impact: Reducing the need for soil excavation and replacement has positive environmental implications. It minimizes disturbance to the natural soil structure and reduces the carbon footprint associated with transporting large volumes of material. Geogrids, being durable and long-lasting, also contribute to the sustainability of infrastructure projects.

Future prospects: Expanding the use of geogrids

The success of the TerraGrid TXG-7 by Hanes Geo Components in this project paves the way for broader adoption of geogrid technology in various construction scenarios. From roadways to railways and parking lots to airport runways, potential applications are vast. As engineers and project managers gain more confidence in the performance of geogrids, their use is likely to become a standard practice in addressing subgrade challenges.

Conclusion

The adoption of the TerraGrid TXG-7 geogrid for subgrade improvement in the described roadway project serves as a testament to the transformative potential of geogrid technology. By effectively addressing the challenges posed by saturated, high PI clay subgrades, TerraGrid TXG-7 not only ensured project success but also demonstrated the broader benefits of cost savings, time efficiency and environmental sustainability. As the construction industry continues to seek innovative solutions for infrastructure development, geogrids such as TXG-7 are poised to play a pivotal role in revolutionizing how we build and maintain roadways. 

Gretchen McInnes, P.E., senior technical sales engineer at Hanes Geo Components, is based in Houston, Texas. She is a licensed professional engineer in the state of Maryland with over 20 years of experience in geosynthetic design of roadways, MSE berms, slopes and walls with a particular focus on design-build solutions. She earned her B.S. in civil engineering from The Georgia Institute of Technology.

All photos courtesy of Gretchen McInnes.

Project Highlights

Rock Prairie Road Construction and Subgrade Stabilization

OWNER: City of College Station, Texas

ENGINEER: Terracon

CONTRACTOR: Brazos Paving, Inc.