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FHWA Repeals its Proprietary Product Rule, Allows Geosystems’ Products to be Specified

By: William G. Handlos, P.E.

Design engineers received good news on September 23, 2019, when the Federal Highway Administration repealed 23 CFR 635.411(a)-(e).

Colloquially known as the “Proprietary Product Rule”, the long-standing provision made it difficult to use patented or proprietary products or technologies in federally funded projects, unless they first received a seldom-granted Public Interest Finding or classified the project as experimental.

Specialty engineered and innovative systems, such as the GEOWEB® soil stabilization (geocells) lineup of products have at times been difficult to specify because there is simply nothing quite like it in the marketplace. While other geocell manufacturers exist, the Geosystems products have patented innovations making it unique in the products’ ability to perform far better than other “or equal” systems.

Now, engineers will no longer be constrained to the lowest common denominator offerings from the marketplace and instead can use technically advanced materials that reduce costs, speed construction and save money.

According to Federal Highway Administrator Nicole R. Nason, “This final rule promotes innovation by empowering states to choose which state-of-the-art materials, tools, and products best meet their needs for the construction and upkeep of America’s transportation infrastructure.”

 

 

 


GEOWEB® — Most Complete Multicomponent Geocellular Confinement System

For information related to the design advantages offered by GEOWEB® geocells, visit www.prestogeo.com.

The Integration of Pervious & Impervious Pavements to Address Green Infrastructure Needs

Written by: Samantha Justice, P.E.

Green infrastructure incentive programs have become commonplace for new construction and redevelopment regulations. Five of the most common incentives include:

  • Development incentives such as expedited permitting, decreased fees, zoning upgrades, and stormwater requirement reductions.
  • Grants.
  • Rebates and installation financing.
  • Awards and recognition programs.
  • Stormwater fee discounts.

A subset of green infrastructure, stormwater management usually includes the consideration of pervious/porous pavements. Traditional asphalt and concrete parking lot surfaces create significant stormwater runoff, and many municipalities do not allow them in expansion or new build situations.

When the entire parking area is constructed using a porous pavement system, stormwater concerns are greatly reduced. Depending on the type chosen, pavements that return rainwater to the aquifer nearly eliminate stormwater runoff and reduce sheet flow and point load erosion problems at the pavement edges. They also reduce the need for additional stormwater infrastructure to convey the water away from the area. Integrating porous pavement systems with asphalt and concrete surfaces can reduce such failures and reduce or eliminate the need for stormwater conveyance channels, pipes, and swales. As a result, downstream stormwater pipe systems see less silt and water, which requires less maintenance and less capital expenditure for upsizing stormwater pipes.

Increase Parking Capacity

Expanding parking areas with porous pavement can have a neutral effect on the existing stormwater loading or, in some cases, can even decrease existing loading.

  • In cases where existing parking areas drain to internal inlets, additions self drain but seldom offer any benefit to existing hard surfaces.
  • In cases where parking areas sheet drains in the direction of the parking capacity addition, the new porous surface can go beyond self-draining and can cut off sheet flow and absorb hard-surface runoff. Of course, you must be careful not to overload the new porous system with sediment.

 

 

 

 

 

 

 

 

 

Integrating Permeable with Impervious Pavements

Not all new-build parking lots need to be 100% porous. A combination of pervious and impervious surfaces can solve stormwater concerns and heavy traffic loading expectations. Using asphalt or concrete surfaces in the drive lanes of parking lots alleviates stresses on the system from repetitive passes from vehicles and ensures that all types of vehicles can use the lot. Joined to these drive lanes can be adjacent porous parking stalls, controlling stormwater runoff and eliminating the need for inlets and conveyance systems. While permeable infill promotes fast infiltration, the base depth may be designed to suit the stormwater needs of the site, allowing for storage and natural percolation.

 

 

 

 

 

 

Semi-rigid resin-based porous pavement units may be filled with either aggregate or topsoil, allowing for customization of parking lots for aesthetic appeal while considering intensity and frequency of use. The permeable paver units are easily cut to seamlessly align with hard-surface pavements (permeable pavers, asphalt, concrete), even along curved lines. Impervious surfaces can be painted for centerlines and turning lanes. Porous pavement units offer delineators, allowing parking stall lines and other separation markers. Parking stops and signs can be easily installed over porous pavement units, so there are no limitations when it comes to fully outfitting parking areas for a project’s needs.

The Benefits of Porous Pavements in Pavement Design

Whether porous pavements are included in all or part of a green infrastructure pavement project, the benefits they offer for reducing runoff and stormwater infrastructure size/need, protecting watersheds, and reducing cost are significant.

Presto Geosystems offers the GEOBLOCK® grass and GEOPAVE® gravel porous pavement systems to help control stormwater, meet load requirements and suit landscape plans.

See our Myth Busters Blog Series for how the units eliminate typical concerns about using porous pavements.

For more information on porous pavements, visit our web page: Porous Pavements.

    

 

Are you using the right construction access mat for the job?

By: William G. Handlos, P.E.

Research shows that GEOTERRA® and GEOTERRA® GTO structural mats provide a ground-surface reinforcement layer to support heavy loads over soft subgrades. More cost-effective than other reinforcement mat systems, the GEOTERRA mats can be used for temporary or permanent applications and are reusable. Offering high crush and flexural strength, the GEOTERRA mats have demonstrated the ability to handle the forces from some of the heaviest wheeled and tracked vehicles under severe conditions.

Scope of Test:

The University of Kansas Geotechnical Laboratory tested the performance of the GEOTERRA and GEOTERRA mat systems over weak to intermediate subgrades with CBR values ranging from 1% to 4%. They conducted a total of 12 tests to identify threshold and limit conditions, create a data-set for modeling, and determine the equivalent crushed aggregate base.

Testing Procedure:

Test sections were subjected to 40 kN (9 kip) cyclic loading on a 300 mm (12 in) diameter plate. Earth pressure cells were placed over of the subgrade to measure vertical interface stress distribution. Loading plate displacements were measured by the displacement transducer inside the actuator.

Test Observations:

The following conclusions were determined for the GEOTERRA and GEOTERRA GTO Structural Mat Systems:

  • The GEOTERRA mats provide additional support for weak to intermediate subgrade subjected to cyclic loadings by reducing permanent deformations and rate of increase in the permanent deformation of the subgrade.
  • The GEOTERRA GTO mats was most effective in cases of larger permanent displacement.
  • The vertical interface stresses between the mat and the subgrade close to the center of the loading plate decreased with an increase of loading cycles. This result is different from that for the aggregate base over the subgrade, in which the vertical interface stresses close to the center increased with the number of loading cycles.
  • Both GEOTERRA mat systems performed similarly to the 12-inch (300 mm) crushed aggregate base over 2% and 4% CBR subgrades.

Test Conclusions:

  • Both GEOTERRA and GEOTERRA GTO mats decreased interface stresses at the load point, which reduces soil movement and ultimately leads to a significant reduction in rutting.
  • Although subjected to rigorous point load testing, the GEOTERRA mats received no significant damage.
  • The testing data proved that the GEOTERRA mat system performed similarly to 12 inches (300 mm) of crushed aggregate base in controlling permanent deformations over 2% and 4% CBR subgrades, with the GEOTERRA GTO mat system performing similarly, but slightly better.

Modular polyethylene construction access mats are lightweight, easy to place without the need for heavy construction equipment, and particularly useful when speed of placement and removal are a factor or when space is at a premium.

To get more information about GEOTERRA mats, go to www.prestogeo.com/products/construction-mats/geoterra-construction-mats/.

Porous Pavements Myth Busters: Cost

Written By: William G Handlos, P.E.

Does a porous pavement solution cost more?

Porous pavements are less expensive to install than impervious concrete or asphalt when you consider total project costs. When evaluating parking lot construction costs for porous pavements vs. impervious alternatives, you must consider the following cost “buckets.”

Traditional pavements such as bituminous asphalt or Portland cement concrete enjoy low cost and ubiquitous installation contractors. This information may lead one to think that choosing a porous pavement would lead to higher overall project costs, but that is a myth because almost everything else about traditional parking lot construction is far more expensive than the porous pavement alternative. Traditional hard-surface pavements require inlet structures, castings, and covers for inlets and manholes, underground pipes, outfall structures, and detention ponds.

Costs & Maintenance of Stormwater Ponds

Detention ponds have three major cost drivers. Land costs to locate a pond can vary wildly depending upon commercial real estate values, but it is not unusual for land to be upwards of $250,000/acre even in small markets. The impact of the land utilized for detention ponds does not end there.

Lost rental or income value is another cost consideration. Ponds take up valuable commercial or residential real estate, representing a continual annual and growing cost.

Finally, there is the detention pond construction cost and higher liability costs.

An additional consideration is safety and aesthetics. The word “pond” often calls to mind pleasant images of fish jumping and ducks paddling; however, ponds constructed for stormwater management purposes are rarely attractive from a safety perspective or aesthetics standpoint.

retention pond retains water as it percolates into the soil below. Retention ponds pose a safety concern to children and can be especially dangerous in wet conditions because the slopes make it very difficult in rain and snow to escape once a child slides down the pitch.

It is difficult to mow close to the edge, and, as a result, tall grass and weeds end up collecting blowing trash. Fences placed for safety create garbage traps too. Additionally, the cyclone fence does not make for a very appealing aesthetic.

detention pond’s primary purpose is to slow the water down from leaving the site, and these structures experience similar challenges. Both types of stormwater ponds are prone to collecting floating garbage and wildlife. This excess of organic matter causes sedimentation to build up at the bottom of the pond, reducing capacity and choking off infiltration.

A wealth of research proves that porous pavements contribute to an overall reduction in project cost and hazard mitigation while meeting aesthetic requirements. With porous pavements, stormwater detention is built right into the open-graded base course to a depth required for the site, so runoff is captured at the source.

The University of New Hampshire Stormwater Center put together a case study showing the economic advantage of porous pavements. The concepts in this case study are valid for a wide range of porous pavements, including modular pavers such as the GEOPAVE® Gravel Pavers and GEOBLOCK® Grass Pavers.

When comparing porous pavements to traditional pavements, make sure you consider all of the costs and safety implications that come with traditional pavements.

Choosing a green solution doesn’t have to cost more.

For more information on porous pavements, visit our web page: Porous Pavements.

    

 

Porous Pavements Myth Busters: Snow Removal

Written By: Samantha Justice, P.E.

What You Need to Know About Removing Snow from Porous Pavements

Vehicle and pedestrian use on porous pavements don’t stop because it’s winter. Roads need to be plowed, parking lots need to be cleared, and walking paths need to be snow and ice-free for safe use. This is true for all surface types: concrete, asphalt, and porous pavements—however, it is a common misconception that snow removal is more challenging with porous pavement systems.


Myth Busted: Snow removal on a Porous Pavement System (PPS) is easy!
Get the answers below to the frequently asked questions about removing snow from plastic, modular type porous pavers.

 

Can I Apply Salt to Porous Pavements?

Applying salt or ice melt chemicals to gravel-filled PPS surfaces encourages snow and ice to melt, the same as it would on a concrete road.

Most porous paver units are made with High Density Polyethylene (HDPE), a strong plastic that has a high resistance to environmental factors and is chemically inert. Cold temperatures and freezing and melting snow or ice will not cause damage or deformation to the paver material. Most importantly, HDPE is chemically stable, so it will not react to applied deicers, including road salt.

The added benefit to using a PPS is that the melting snow will infiltrate through the infill material and into the sub-base, minimizing the amount of surface water that could refreeze over time. With the ice at the surface removed or reduced, the insulating effect is gone, reducing the need for deicing salts by up to 70%. And you don’t need to worry about freeze-thaw issues in the base of the PPS either, because of how the open-graded aggregate’s high void space gives the water room to expand as it forms to ice. See More on Freeze-Thaw >>

Of course, deicers should only be used on aggregate infilled PPS as they would do damage to vegetated paver systems.

Can I Apply Sand to Porous Pavements?

Using sand, saw dust, kitty litter, or other abrasive materials on the surface of fallen snow can create traction to prevent slips, but doesn’t promote melting. More importantly, sand is only effective when it is on top–if it is buried or when the snow melts, the sand is ineffective.

Sand should not be used on PPS because it will eventually seep into the open-graded aggregate base underneath the paver units, causing it to clog. A clogged system will not work properly, leading to excessive maintenance requirements in the spring. Avoiding sand and other fine-grained materials will help keep the PPS in ready-mode for the next snowfall.

Can I Use a Snowplow on Porous Pavers?

When heavy snowfalls occur, you cannot rely on deicing alone. For residential or small porous pavement areas, using a hand shovel is perfect for clearing away the snow; but for larger areas, snowplows are the way to go. When plowing over any gravel areas—especially gravel-filled porous pavers–snow blade shoes are recommended. The snow blade shoes will protect the paver units, while avoiding excess wear or movement of the gravel material. When using the blade shoes, snowplows have no special requirements. Simply run the plow according to standard use.

If a blade shoe is not available, the plow’s blade should remain 1 to 2 inches above the paver system to avoid damaging the units or catching on the system. Typically, there isn’t a need for deicers as the warmth of the ground permeates through the open-graded base course and melts the thin layer of unplowed snow—but if desired, deicers can be applied to melt the remaining snow.

How Do I Remove Snow from Grass Pavers?

If the porous pavement system has topsoil infill and sprouts vegetation, then snow removal is typically not required. The grassed area should look and act like a regular lawn, so snow can accumulate and melt naturally. When the snow melts in the spring, maintain the vegetated porous pavement area in accordance with regular landscaping plans.

In the case where snow removal is required—such as an emergency lane—simply leave the blade up 2 inches and allow the remaining snow to melt off naturally. It may be necessary to have visibility poles marking the boundaries of the porous pavement area.

Making Winter Surfaces Safer

As you can see, snow removal on porous pavement systems is easy. Roads, parking lots and walking trails will not only be safer, but with a porous pavement system, drainage and runoff during the spring melt will not be an issue either.

Presto Geosystems offers the GEOBLOCK® grass and GEOPAVE® gravel porous pavement systems to help control stormwater, meet load requirements and suit landscape plans.

Watch this video to learn more about our PPS and start building green today.

For more information on porous pavements, visit our web page: Porous Pavements.

    

Porous Pavements Myth Buster: Clogging

Written By: Bill Handlos, P.E.

Not All Porous Pavements Clog

Well-designed porous pavement systems resist clogging

When designing porous pavement systems, it is important to consider the effects of silt, grit, sand, and other fine material that can slow or stop water from infiltrating. However, it is a common myth that all porous pavement systems eventually clog. A good PPS system design, simple but effective site design, and careful construction inspection and field guidance can all but eliminate the clogging threat.

System Design Do’s and Don’ts

Cross-sections will vary according to the porous pavement selected, but following some simple practices can ensure a successful system with long-lasting percolation.

 

 

Never place filter fabric immediately below the porous pavement surface. Whether you are using pervious concrete, porous asphalt, polyethylene injection-molded paving block (such as GEOBLOCK vegetated or GEOPAVE aggregate PPS), or concrete paving stone, your cross-section should allow free flow from the paving layer to the base and storage layers. The last thing you want is to trap water in your pavement layer. Surprisingly, at least one aggregate PPS manufacturer sells their product with a filter fabric attached to the bottom of the units.

Always use a filter fabric or other separator at the bottom of the base layer if the subbase contains fines that can move up into the open-graded base course when saturated.

Choose wisely when specifying choker course and base gradation. A choker course is not necessary for polyethylene molded block products since they ride on the surface of the open-graded base course but is necessary for brick pavers, pervious concrete, and porous asphalt. You should select choker course materials carefully to prevent them from migrating into the base and creating settlement problems. Choosing a material that is too fine may cause settlement, and choosing one that is too coarse will prevent your paving surface from placing properly.

 

Common Site Design Errors

 

Drainage is still important but for different reasons. For impervious surfaces, positive drainage to avoid puddling is standard. For pervious surfaces, one has to consider drainage below the surface. The design needs to consider water moving through the base to the low spot of the pavement area. Be cautious not to discharge from the base up through the surface of the pavement course. Consider a 50-foot long pervious pavement driveway at a 4% slope. There would be 2 feet of fall from the high-end to the low-end, and in a heavy rain event, water could become transient and flow out of the pavement at the low side. This horizontal transportation of water carries silt and sand that would become concentrated at the low-end of the pavement structure.

 

Another way that site design could create clogging is a lack of consideration for off-pavement sheet flow. Whether it’s leaves, grass clippings, or silt and topsoil, pavement-adjacent drainage can transport contaminants in heavy loading conditions. Cut-off swales and site contouring can prevent this from happening.

Common Installation Errors

 

Pervious concrete should be a very stiff and dry mix. Adding water to the mix for workability at the site leads to the paste being pulled down by gravity and settling at the bottom of the concrete lift. With that thin layer of paste hardening, the high-volume water flow gets caught like a perched water table within the pervious concrete. This is not only bad for volume flow, but cold-weather climates can create a standing water layer.

Gradations with a high degree of fines should be avoided for both aggregate polyethylene block style pavement as well as for open-graded base course material. While there is no need for washed material, delivering material with high fines content essentially pre-contaminates your porous pavement system.

In some areas, river rock or brownstone is plentiful and inexpensive. The specifier should fight the urge to accept such stone as a substitute for crushed aggregate base course. Good porous pavement locks up and carries load well.

Some resin-based block style products specify sand bases. While initially, coarse sand can drain adequately, it will quickly become clogged, water will saturate, pore pressures will rise, and saturated conditions will lead to running.

How to Guarantee Success

Intelligent design by experienced manufacturers and engineers and installation by seasoned contractors will ensure success.

For more information on porous pavements, visit our web page: Porous Pavements.

    

 

Porous Pavements Myth Buster: Winter Durability

Written By: Bill Handlos, P.E.

Properly designed porous pavement systems will not be damaged by the dynamics of freeze-thaw cycles.

For decades, civil engineering roadway designers have been trained to use positive drainage, crack sealing, and sealcoating to keep the area under pavement dry. The prevailing mentality was to use a well-graded, tightly compacted base under impervious concrete or asphalt wearing surfaces. When water gets between the well-graded base and the impervious surface, frost conditions would lift pavements, weaken the base structure, create potholes and, in general, wreak havoc with the life of the pavement.

  

So, it is not surprising that age-old tenets related to moisture, seepage, and freeze-thaw cycles get mistakenly applied to porous pavement systems.

What makes well-designed porous pavement cross-sections so resistant to the power of freezing and expanding water? The answer is space. Poorly graded crushed aggregate offers up to a 40% void ratio, which gives water a place to move and expand upon freezing, and a network of pathways to drain.

High void ratio systems allow the Earth’s natural warmth to move up from below the frost line into and through the open-air system just as water and ice-melt move through the system. If the water can’t permeate into the ground and becomes trapped in the open-graded base system, the voids allow expansion of the water as it forms into ice.

How Freeze-Thaw Affects Porous Pavement

There is more than one freeze type. There are dry freeze and hard dry freeze conditions that describe regions with low precipitation and multiple freeze-thaw cycles or only one or two freeze cycles, respectively. Neither of these freeze types challenges porous pavement systems because they lack moisture.

There are wet freeze regions having 15+ freeze-thaw cycles that require 6 to 12 inches of open-graded base course to safely allow expansion of the water that percolates and drains through the pavement and base throughout the cycles.

Then there is the more challenging hard wet freeze. This is the condition described by areas that have moderate to high precipitation combined with a frost depth that develops over several months. The National Ready Mixed Concrete Association offers a solid set of recommendations defining open-graded base course depth and the porous pavement depth, based on 65% of the maximum frost depth for the area. An area that gets 24 inches of frost depth should design for a 16-inch total pervious cross-section. The 16 inches includes the porous pavement, the open-graded base course, and any pervious subbase.

 

Concerns with freeze-thaw negatively affecting the performance of porous pavements are understandable but simply a myth. Because of their high void space and ability to allow expansion of water to ice, freeze-thaw cycles have little effect on porous pavements.

 

You can have all of the benefits of porous pavements with the comfort of knowing that freeze-thaw cycles will not damage your porous pavement.

For more information on porous pavements, visit our web page: Porous Pavements.

For more information on porous pavements, visit our web page: Porous Pavements.

    

 

Porous Pavements Myth Buster: Winter Maintenance

Written By: Bill Handlos, P.E.

Winter Maintenance for Porous & Pervious Pavements

Porous pavement systems are a great way to reduce the amount of stormwater runoff on your site and incorporate Low Impact Development (LID) practices. One of the simplest ways of creating a porous pavement area is to confine unbound aggregate in a rigid paving unit such as the GEOPAVE® Aggregate Porous Paver. The GEOPAVE system is similar to pervious concrete and porous asphalt solutions, but is usually both less expensive and easier to install.

Porous Pavements Are Difficult to Maintain in Winter Weather Conditions.

 

NOT TRUE! The GEOPAVE Aggregate Porous Paver system is easy to maintain, and requires no special equipment. GEOPAVE parking lots or low volume roadways can be maintained in much the same way as a regular concrete or asphalt surface.

An unbound aggregate system has many maintenance benefits over other porous pavement systems. Look at the table below and you’ll see how the GEOPAVE system beats pervious concrete and porous asphalt every time.

 

 


(Click Chart to Zoom)

 

The GEOPAVE rigid porous pavement system is comparable to standard paving materials, and a cut above other porous pavement systems. GEOPAVE systems have all of the benefits of hard surface porous pavements—fast infiltration, reduced runoff, no traffic restrictions—with a safer winter surface, much lower cost, and none of the maintenance hardships.

For more information on porous pavements, visit our web page: GEOPAVE Permeable Gravel Pavers

    

 

Railroad ballast performance improvement using GEOWEB® Geocells

Each year railroads must allocate a significant portion of their capital and maintenance budget toward the creation and upkeep of high-quality ballast layers. Enduring, well-designed ballast is quite literally the foundation on which a successful rail line operates. With ballooning rail traffic carrying heavier loads than ever, GEOWEB cellular confinement (geocell) effectively takes the pressure off critical ballast systems.

Oregon State University (OSU) recently performed state-of-the-art, three-dimensional dynamic Finite Element modeling to analyze the reinforcing benefit of GEOWEB geocells in railway applications. Completed in cooperation with the University of Kansas (KU), who simultaneously performed a testing program of Geocell-reinforced ballast placed over weak subgrade.

The digital modeling results were reinforced by the laboratory tests and showed a significant decrease in settlement of the railway ballast when GEOWEB confinement was used. Using the GEOWEB system not only decreased settlement but also reduced pressure on point-to-point aggregate load transfer contact. This resulted in less damage to ballast aggregate particles leading to less progressive deformation and longer maintenance frequencies of the entire ballast embankment. In short, more cycles mean less track down-time for maintenance.

The research results were clear. The benefits of applying GEOWEB Geocell confinement for reinforcement of real ballast over weak subgrades includes:

  • Significant decrease in settlement of the railway ballast. GEOWEB confinement influence reduced settlement by to up 50% under heavy freight loadings over weak sub grades.
  • Decrease in subgrade interface pressure by nearly 50% for weak subgrades. The decreased pressure in subgrade results in lower subgrade settlements.
  • Increase in ballast resiliency after many cycles—resulting in decreased rate of cyclic settlement.
  • Decrease in lateral heave and movement of the ballast material.
  • Redistribution of vertical stresses on the subgrade—resulting in higher shear strength and reduction in plastic deformation.
  • For the largest loading conditions used in the analysis, the strains in the GEOWEB geocell were low (less than 1%) and within the elastic range for typical geosynthetic materials. The maximum tensile strains were localized at the bottom corners of the GEOWEB cells, illustrating the importance of adequately durable seams.
  • Strains in the GEOWEB ballast layer were low (less than 1%) even under heavy, freight loadings over very soft sub grades. Stress concentrations were found at the seams, highlighting the importance of GEOWEB seam strength during loading condition.

A Better Built Ballast

The benefits of GEOWEB confined ballast are substantiated through rigorous testing. Conventional ballast reinforcing materials (eg geogrids, Hot Mix Asphalt (HMA)) do not have the strengthening attributes that GEOWEB geocells can provide, especially in soft subgrades. Building a more stable ballast layer with less settlement, higher shear strength, and less maintenance requirements is possible when built with GEOWEB geocells.

For more information, see https://www.prestogeo.com/applications/railroad/aar-ttci-performance-tested/.
Request an on-site technical presentation: https://www.prestogeo.com/lunch-and-learn/

Why Geocells Outperform Geogrids for Road Construction

Written By: Bill Handlos, PE, Director of Presto Geosystems

Geocells (cellular confinement) offer a more effective and practical 3D design solution to load support challenges than multilayered 2D geogrid efforts. Geocells transfer applied loads instantaneously, delivering practical soil stabilization in a product that is fast and easy to install.

Blog: Geogrids Product      Blog: GEOWEB Geocells Unpaved Roads

How do geogrids work?

Geogrids rely on rutting, displacement and lateral movement of the road material to activate the load support reaction of the product. As shown below, failure of the driving surface must occur before the geogrid reacts. As a result, rutting and soil displacement is a prerequisite reality to the system. Since the geogrid is two-dimensional, material not located directly within the plane occupied by the geogrid is free to move, shift and displace.

Blog: DiagramIt is essential that geogrids are placed in a flat or a pre-tensioned manner—but that is not practical in a construction environment. It is common to see geogrids unrolled over a prepared grade with an undulating surface. As aggregate is placed over the top of the geogrid, the material kinks and waves, further warping the 2D plane. The geogrid is rarely pulled tight during installation which does not allow full tension under load.

 

 

Geogrids are difficult to install in soft subgrades

In cases where subgrade is particularly poor, over-saturated, or already damaged by rutting, geogrids are even more difficult to place flat and tight as recommended. Soft subbase does not support medium or heavy construction equipment to place and spread the base layer over the geogrid without deforming the geogrid even further. The overall deformation creates an uneven geogrid layer that is poorly suited to function as intended.

Often, geogrid manufacturers recommend two, or even three layers of geogrids to create a stiffened aggregate cross-section. This approach improves load support performance of the geogrids, but is time-intensive, as each layer must be unfurled, covered and compacted separately. Cost of installation and materials double and triple with the additional layers.

How do geocells work?

Geocells are 3D structures that utilize the cell hoop strength, passive earth pressures, and particle confinement to create a stiff mattress layer that resists wheel loads immediately upon impact and without the partial driving surface failure required by geogrids. Load induced stresses are transferred from the infill particles to the cell wall and counteracted by hoop resistance and passive resistance of adjacent cells.

Blog: GEOWEB Geocell Load Support Diagram

Workers expand geocells over the subbase quickly and easily and it is not critical that the geocells be pre-tensioned or placed perfectly on-grade. Loaders, bulldozers and bobcats are employed to fill the geocells. Loaded dump trucks can back over ‘just-filled’ geocells with no damage to the product and no effect on the performance of the material.

Unlike geogrids, geocells are effective with a wide variety of infill, and are not limited to the high quality aggregate required for geogrids. Sand, fine aggregate, gravel or breaker run, all see their properties enhanced by the strength of high density polyethylene (HDPE) geocells. The ability to use on-site infill or locally available materials can yield increased savings to the project.

Geocells are ideal for installation over soft soils

No equipment is necessary to expand geocell sections, so they can be placed over the softest of subbases and low-pressure equipment is not required to infill the cells. Simply back up full-size loaded dump trucks, empty the payload and spread the granular material in and over the geocell.

Geocells Proven Performance

Geocells have been successfully improving road life of paved and unpaved highways, access roads and work platforms for 40 years. Since the United States Army Corps of Engineers (USACE) co-developed the technology in partnership with Presto Products, thousands of GEOWEB® geocell load support projects have saved millions of dollars in construction costs and provided three-dimensional stabilization simply not available with the use of traditional geogrids. Browse our project case studies, photos and videos here.

Request an on-site technical presentation to learn more about the GEOWEB® Geocell Confinement System.