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Understanding Hoop Stress in Geocells

Written By: Michael J. Dickey, P.E., Samantha Justice, P.E., Bryan Wedin, P.E.

When constructing roadways over soft soils and weak subgrades, geocells are one of the most powerful value engineering tools available to the civil engineering and construction industries today. Understandably, some engineers may be apprehensive about using a geosynthetic product for which they have an incomplete technical understanding. So, if you’ve ever wondered how geocells work in load support applications – and the relationship between lateral confinement and hoop stress – you’ve come to the right place.

Generally speaking, geocells can be used to alter the geometry of a soil pressure bulb beneath an applied load through a phenomenon known as the mattress effect. Key to the mattress effect is a physical mechanism unique to geocells known as lateral confinement. When a load is applied to a geocell-reinforced layer, lateral earth pressures develop within the infill material, which is confined laterally by the cell walls against movement, in turn developing upward shear resistance along wall interfaces throughout the interconnected network of cells. In essence, lateral confinement converts horizontal earth pressures into upward resisting shear forces.

 

Hoop Stress in Geocells

 

When combined with suitable base reinforcement (i.e., an enhanced woven geotextile), it becomes possible to construct over very weak subgrade materials, including those with standard penetration resistance (SPT-N) values less than 2 blows per foot (CBR < 0.5%), where most planar geosynthetic products, such as geogrids, would otherwise fail.

Now, where does hoop stress come into play, and how does it relate to lateral confinement?

Hoop stresses develop within the cell walls as earth pressures propagate radially in response to an applied load at ground surface. In other words, the same earth pressures responsible for developing interface friction between the geocell and the infill material also result in hoop stresses within the cell walls. Although not perfectly cylindrical, geocells can be envisioned to behave similarly to an interconnected network of pressurized cylinders, wherein hoop stresses are a function of the net pressure that develops due to the internal and external pressures acting within and around each cell.

In this manner, radial pressures that develop within each cell are resisted by those that develop in the adjacent cells, and hoop stresses may be estimated using the classic equation for hoop stress for a pressurized thin-wall cylindrical vessel:

σH = pnet*(D/2t)

Where,

σH = hoop stress

pnet = net pressure = pipe

pi = internal pressure

pe = external pressure

D = geocell diameter

t = wall thickness

The internal active earth pressure in a cell directly beneath a point load can be calculated using Boussinesq’s point load stress equation. Concerning external, or “passive”, earth pressures in adjacent cells, Emersleben (2009) investigated the interaction between hoop stresses and passive earth resistance in geocell systems and observed that lateral pressures in adjacent cells decrease exponentially with increasing distance from the actively loaded, or “source” cell(s) – in effect, defining a pressure gradient. Based on Emersleben’s findings, it is possible to evaluate the net earth pressure that develops between the interior and the exterior of a cell wall, using the thickness of the cell wall as the distance between two points along the defined pressure gradient line.

Not surprisingly, the largest net earth pressures, and largest hoop stresses, occur in cells directly beneath the perimeter of the load footprint, the wheel contact area in the case of vehicle loads. Based on this, it is possible to estimate the maximum hoop stresses that would be expected to develop in geocells in response to standard AASHTO load conditions.

Accordingly, the table below summarizes the estimated hoop stresses that would be expected to develop under standard AASHTO load conditions in a 6-inch geocell-reinforced layer overlain by 2 inches of aggregate wearing course. The calculations assume a 9.5-inch diameter geocell infilled with coarse sand having an internal friction angle of 32 degrees.

AASHTO Load Wheel Load (lbf) Tire Pressure (psi) Estimated Hoop Stress (psi) Tension in Cell Wall (lb)
AASHTO H/HS10 8,000 60 44 16
AASHTO H/HS15 12,000 85 63 23
AASHTO H/HS20 16,000 110 82 30
AASHTO H/HS25 20,000 125 96 34

As shown, the corresponding tensile forces that develop under working load conditions are relatively modest due to the lateral confinement effect of the adjacent cells. When compared to the typical yield strength for most high-quality HDPE geocells, the above-referenced tensile forces are well within the elastic region for the material, and would not be expected to undergo any permanent deformation or “creep” over time, even when subject to repeat traffic loads over many years.

With regard to strain, the elastic response of the geocell-reinforced layer will ultimately be governed by the elastic properties of the infill material and provided that suitable granular infill is used, the development of any significant strain in the cell walls will be heavily constrained by the effects of lateral confinement. Because of this, the actual strain that develops in the cell wall will be far less than the amount of strain represented on a typical stress-strain curve generated from laboratory tests such as ISO 10319 or ASTM D4595 where samples are subjected to tensile forces in an unconfined state.

This is not to say that hoop stress is not important. Development of hoop stress is essential for the proper engagement of the lateral confinement mechanism. Moreover, the ability to estimate hoop stresses under specific project circumstances can be useful as it allows designers to develop a preliminary (and very conservative) understanding that tensile forces in the cell wall will remain within the elastic region for the material (with the caveat that many laboratory test methods such as ISO 10319 ignore the effects of confinement, and therefore tend to overestimate strain levels).

In terms of long-term hoop integrity as it pertains to the cell wall (junctions are another matter altogether), dynamic mechanical analysis using a method such as ISO 6721 allows for more accurate characterization of expected material behavior under repeat dynamic loads at reduced strain levels. In general, provided the product is a high-quality HDPE geocell with a flexural storage modulus of at least 116 ksi (800 Mpa) and a 100-year durability rating (ISO 13438), the product can be expected to perform as intended throughout the life of the project.

References:

Emersleben A. et al (2009). Interaction Between Hoop Stresses and Passive Earth Resistance in Single and Multiple Geocell Structures. GIGSA GeoAfrica 2009 Conference, Cape Town 2 – 5 September 2009.

Building Climate-Resilient Infrastructure Using Geosynthetics

When extreme weather events occur, communities are often left to grapple with the devastating effects. An increase in extreme weather patterns, coupled with aging or inadequate infrastructure, amplifies the often dangerous and costly damage that ensues—especially for vulnerable communities living in low-lying areas.

According to a recent study, the United States could see a 26.4% increase in flood risk by 2050, which could cause significant damage to existing infrastructure. For this reason, it is vital to build resilience into infrastructure projects to mitigate climate risk and ensure the long-term reliability of critical infrastructure.

Incorporating geosynthetics into infrastructure can improve the ability of communities to withstand and recover from extreme weather events. For example, in hurricane-prone parts of the country, designing robust access roads along power transmission lines allows repair crews to safely and quickly restore power to communities that might otherwise be without electricity for days or even weeks. Geosynthetic products, such as geocells, can be used to construct reliable access roads along transmission infrastructure, which often traverse very remote areas with difficult terrain and very soft ground conditions. Through an interconnected honeycomb-like network, geocells confine and stabilize soils that would otherwise be unstable under loading.

When used in load support, slope stabilization, channel protection, and retaining wall applications, geocells are a powerful weapon against the long-term effects of climate change. This article discusses several examples where GEOWEB® geocells were successfully used to help communities adapt to, and recover from, extreme weather events.

GEOWEB Porous Pavements Used for Rebuilding Roads, Replacing Transmission Lines Damaged During Hurricane Michael in Florida’s Panhandle

Hurricane Michael caused extensive damage to Florida’s power grid network, leveling more than 100 transmission towers in a 34-mile right-of-way from Port St. Joe to Callaway. This right-of-way crosses swampy, remote, and hard-to-reach areas, making rebuilding the grid even more challenging. This extremely wet, muddy ground prevented repair vehicles from accessing the area. Helicopters were employed to transport the new steel towers installed on-site.

Accessing the lines for maintenance would require a stronger roadway to support heavy vehicles in the wettest areas. The GEOWEB Load Support System was used to make the roads operational and improve performance in saturated conditions.

The GEOWEB system was placed over an enhanced geotextile and filled with crushed aggregate to create access roads across critical wetlands and stabilize pole pads. The access roads and pads are permanent.

GEOWEB Utilities

GEOWEB Geocells Repair Storm-Ravaged Trail & Maintenance Road

In the spring of 2018, several storms violently swept through areas along southern Maine’s coastline, devastating the beaches and trails of Fort Foster—a town-owned park in Maine. Known as “nor’easters,” these destructive storms form along the east coast, bringing strong winds, rain, and flooding to the New England states. As the storms rolled past, the damage was visible to Fort Foster and Kittery Point’s 2.1-mile-long shoreline walking trail and maintenance road, as well as on the slopes leading down to the beach.

The park’s goal was to repair the damage and protect the slopes, maintenance road, and recreational trail from future storm damage. The GEOWEB® Soil Stabilization System was chosen to restore and protect two sections of the park’s shorelines and trails.

By using the GEOWEB System, the park was able to armor the maintenance road, recreational trail, and slopes from future storm events. Since being installed in 2018, the GEOWEB Load Support and Shoreline Protection Systems continue to perform as designed, allowing the community to once again enjoy the trail system and local beaches.

GEOWEB Trail

GEOWEB Hard-Armored Shoreline Protection System Protects Vulnerable Riverbank from Erosive Forces

The extreme El Niño event caused the western Pacific to warm, developing atmospheric convection and increased rainfall. The storm events caused catastrophic flooding and severe erosion in the eastern equatorial region of Ecuador and Northern Peru. A portion of the Zarumilla River, located in the remote Tumbes region in Northwestern Peru, was experiencing severe erosion and required a shoreline protection solution to prevent further deterioration of the riverbank.

The GEOWEB® Shoreline Protection System was selected to protect the Zarumilla riverbank against future storm events. The GEOWEB system with concrete infill provides economical, hard-armored protection of slopes and channels exposed to high flow velocities and high shear stresses. The system has been proven to withstand sustained flow velocities over 36 ft/s (11 m/s) and shear stresses of 20.9 psf (1.0 kPa), outperforming rip-rap, gabions, and other conventional hard armor strategies.

Zarumilla Shoreline GEOWEB

The product was shipped to the site in September 2020, and installation was complete by December 2020. The project was completed on schedule and within budget. The GEOWEB® Shoreline Protection System is performing to expectations and will provide much-needed protection to the Zarumilla River and the communities that depend on it when the next major storm hits.

GEOWEB Geocells Used for Erosion Protection of Canal Floodwall

Erosion of the 17th Street Canal’s flood protection system was a major concern for the Southwest Louisiana Flood Protection Authority-East. The Authority required a solution to protect the canal’s slope against erosive forces and prevent a floodwall breach in the event of a tropical storm event.

To mitigate channel slope erosion, engineers chose the GEOWEB® Confinement System to stabilize the slopes along the Metairie side of the drainage channel. By confining the infill material, the GEOWEB system prevents flow from causing scour and erosion on slope surfaces.

The construction company installed approximately 380,000 square feet of GW40 (mid-cell size, six-inch deep panels) over a woven geotextile along the canal’s slope and infilled the cells with crushed aggregate sized based on research and testing at Colorado State University hydraulics lab.

17th street canal

The GEOWEB System:

  • Allows the use of smaller, less expensive rock—even waste rock which decreases installation and transportation costs.
  • Creates a permeable, cover when drainage is desired but vegetation cannot be established.
  • Resists high velocities and tractive forces.

Design Support & Resources for the GEOWEB System Applications

The engineering team at Presto Geosystems works closely with engineers and project planners, offering free project evaluation services and on-site support. Our recommendations will deliver a technically sound, cost-effective solution based on four decades of accredited research and testing data. Please contact our knowledgeable staff and network of qualified distributors and representatives to discuss your project needs today.

Request Free Project Evaluation

Meet the Presto Geosystems Team: Get to Know Bryan

Bryan and NaomiHow long have you been with Presto Geosystems?

Time flies when you are having fun! I have been with Presto Geosystems going on 14 years. In that time, I got to work with some really great people and enjoyed speaking with Gary Bach on how geocells were invented back in the late 70s and early 80s.

Can you tell us a bit about your background?

I grew up in the Upper Peninsula of Michigan and enjoyed doing all things outdoors. My father was an Olympic ski jumper, so I had no choice but to strap on a pair of skis and follow in his footsteps. I became pretty good and was in three junior Olympics before a bad fall ended that part of my life. I grew up before video games, so we were always outside playing football, baseball or just riding bikes.

After a year at Michigan State University, I attended college at Michigan Tech University in Houghton, MI and graduated with a degree in Environmental Engineering. After graduation, I moved to Green Bay, WI, and worked for Foth & Van Dyke and then Robert E. Lee engineering consulting firms before joining Presto Geosystems.

What attracted you to the world of engineering and geosynthetics?

I was lucky enough to land a wonderful job out of college at Foth & Van Dyke in Green Bay, WI. Foth was a growing consulting firm at the time and the staff was always at the leading edge of technologies. When I started in consulting, geosynthetics were just becoming an option for roadway and earth retention projects. I got to see early on how engineers included geosynthetics in their projects and how the approval agencies accepted them. I guess I’m really showing my age…

What does your job entail? Can you take us through a day in the life as the Chief?

The best part of my job is that every day is different and it seems there are no “typical” days. Our products can solve so many soil stabilization problems that I am blessed to work with engineers all over the world on their challenging projects. It is rewarding to walk away from my computer at the end of the day knowing that the Geosystems Team and our worldwide distribution network work together to make a difference.

What do you like most about your job and/or what do you like most about this industry?

The people and relationship building through the years has been enjoyable. Our industry really works closely to ensure successful geosynthetic projects. I enjoy working on the AREMA, ASTM, and ISO committees and the discussions with the industry experts.

What is the most challenging part of your job?

How do you turn it off? When I first started consulting 35 years ago, we didn’t have the technology we have today. We didn’t even have AutoCAD or personal computers at the time! Everything was done by hand, and I think we understood the calculations better. When you left work, it allowed you to unwind. Today, it seem it is 24/7, especially with the advancements in technology. It can be a challenge to turn it off.

What do you enjoy doing when you aren’t out helping solve the world’s soil stabilization and erosion challenges?

My wife and I stay pretty active, especially in the summers. We live on a golf course, and you will always find us out playing or enjoying a cocktail on the 19th hole! Family is a big part of our life. We are lucky to have four wonderful kids who have moved out of the house and are employed! They have given us three beautiful grandchildren (one more on the way in December) that we love to spend time with and spoil which is what grandparents are supposed to do.

What is your favorite place in the world to visit?

I have been lucky to have traveled all over the world for leisure and work. A few of my favorites include Austria, Switzerland, Australia, and Banff in Canada. If had to pick one it would have to be Punta Cana since my wife and I have the best of times when we visit. We have so many great memories there. We both have stressful jobs, so it is nice to get away, relax on the beach, enjoy some cocktails and let someone else do the cooking.

If you could meet anyone, living or dead, who would you meet?

This is an easy one but hard to decide which person. I am a huge old western movie fan. It is to the point that if I am watching tv and scrolling through the channels and come across one, my wife just gets up and goes to another tv. I would have to pick my top 20, throw them in a hat, and just pick one and would be fine.

What would you name the autobiography of your life?

Never a Dull Moment.

Are material shortages delaying your road construction projects? Here is how to stay on schedule and within budget.

Written by: Bryan Wedin, P.E., Chief Design Engineer

sand filled GEOWEBRoad construction is booming, and this trend is expected to remain strong due to high demand and the Infrastructure Investment and Jobs Act (IIJA), which includes investments across many sectors, including public infrastructure.

Along with this boom, the road construction industry has been dealing with inflation-related cost increases and limited availability of construction materials. The industry has been impacted by supply-chain interruptions and shortages for many roadway materials including lime, cement, and even aggregate. These materials are typically used for roadway base construction, which means road construction projects that use these materials may be subject to delays. Due to these shortages and delays, on-site material or sand-filled GEOWEB® geocells can provide a cost-effective, readily available substitute for base materials–especially where native subgrade conditions consist of weak or soft soils.

GEOWEB® Geocells for Roadway Base Stabilization

The GEOWEB geocells have been used for load support and foundation applications worldwide for more than 40 years. Developed in collaboration with the U.S. Army Corps of Engineers (USACE) in the late 1970s, Presto co-invented the technology now known as geocells or a cellular confinement system (CCS). The early applications of geocells consisted primarily of stabilized, expedient sand roads for military vehicles. In the early 1990s, the U.S. Army deployed over 6 million square feet of the geocellular system to stabilize the shifting desert sands and provide mobility for troops and military vehicles. At the time, the system was dubbed Sandgrid due to its readily available sand infill.

Both the USACE and Desert Storm forces found a solution for building fast access roads across sand landscapes. By utilizing the principle of soil confinement to enhance soil strength, the GEOWEB System turns sand into a load-supporting composite structure that can support heavy-loaded vehicles under repeated load cycles. Since then, the GEOWEB System has also been adopted by State and Federal roadway authorities for domestic road construction across the United States.

Presto Geosystems has endeavored to improve and innovate geocell technology, creating the modern-day GEOWEB® Soil Stabilization System. The GEOWEB geocells are made of 100% high-density virgin polyethylene (HDPE) and do not contain any recycled material, fillers, or exotic polymers—all of which can negatively affect performance. Complete with a full line of accessories for ease of installation and long-term performance, the GEOWEB Soil Stabilization System is the most advanced geocell technology in the industry.

Sand-Filled GEOWEB Geocells for Soil Stabilization

sand filled geocellsGeocells are three-dimensional honeycomb-like structures made of ultrasonically welded strips of HDPE that confine infill material over a specified cell depth and diameter. Through confinement, the GEOWEB system distributes loads laterally and controls shearing, as well as lateral and vertical infill movement.

Compared to planar geosynthetic products such as geogrids—which commonly rely on expensive imported high-quality aggregate—geocells are highly versatile and can be filled with a variety of commonly available and economical infill materials, including sand.

In many cases, geocells allow for the beneficial reuse of on-site materials, eliminating the need to purchase expensive aggregate or imported structural fill. These advantages not only offer the potential for savings in overall construction costs but also contribute to a significant reduction in carbon emissions due to less aggregate/fill processing, transportation, and handling.

The illustration below provides a comparison of four structurally equivalent aggregate sections over a subgrade with a CBR of 0.5%.

GEOWEB Cost Benefit

As shown, the unreinforced aggregate option would require more than 36 inches of aggregate to achieve minimal stability, and the planar geosynthetic option (geogrid + geotextile) would require 26 inches of aggregate. In contrast, the GEOWEB geocells reduce the total section thickness to only 15 inches, and where suitable on-site material is available, it is possible to limit imported aggregate to just the wearing course.

GEOWEB Diagram

The GEOWEB geocells dramatically increase the shear resistance of the infill, which allows the use of lower-quality fill to carry concentrated loads that would otherwise require crushed aggregate to prevent localized, near-surface shear failure. The cellular structure also distributes concentrated loads to surrounding cells, thus reducing the stress on the subgrade directly beneath the load and the required total thickness of the structure.

 

Let Our Engineers Run Design Calculations on Your Next Project. See the Cost Savings For Yourself!

Presto Geosystems’ engineering team works closely with you to provide free project evaluations and on-site installation support. The team at Presto Geosystems is here to provide engineering support from the preliminary stages through construction. Use our free online tools to keep your projects moving forward. The project evaluation will deliver a technically sound, cost-effective solution based on four decades of accredited research and project experience. Please contact our knowledgeable staff and network of qualified distributors to discuss your project needs today.

Request Free Project Evaluation

Presto Geosystems Announces Launch of the ATRA® Wall Key

We are thrilled to announce our newest innovation at Presto Geosystems: the ATRA® Wall Key (patent pending) for the GEOWEB® Retaining Wall System.

The ATRA Wall Key is used to connect adjacent GEOWEB Retaining Wall sections through the GEOWEB material slots (I-slots). The ATRA Wall Key includes an integrated washer at the base of the handle for coverage of the I-slots when connecting adjacent wall sections, frictional barbs for an improved interlock with the GEOWEB sections, and an ergonomic handle with S-shaped contouring for ease of installation.

ATRA tan and green wall keys

The ATRA Wall Keys are the most effective way to connect the GEOWEB Retaining Wall sections, ensuring the long-term success of your project. Made of non-reactive, chemically inert high-density polyethylene, the ATRA Wall Keys provide a more secure and permanent mechanical connection over staples or zip ties, and they are the only geocell connector specifically designed for use in exposed wall face applications. Formulated to withstand weathering and ultraviolet radiation, the ATRA Wall Keys will not corrode or photodegrade, even when exposed to harsh environments. Securing sections with the Wall Keys is faster than using staples or zip ties, requires no tools, and can be completed by one installer with one easy turn.

The new ATRA Wall Keys offer a natural-looking aesthetic by blending seamlessly into our green or tan wall fascia options.

CONTACT FOR MORE INFORMATION
Presto Geosystems
Michael Dickey, PE, Director
E: michael.dickey@prestogeo.com
P: 904-910-1002

“Or Equal” Substitutions in Geosynthetics: Evaluating the Contractor’s Proposed Alternative Amidst Global Supply Chain Disruptions & Rising Costs

GEOWEB sand road

Written by: Michael J. Dickey, P.E., Director of Presto Geosystems

As supply chain issues and project delays continue to wreak havoc in the global geosynthetics industry, Presto Geosystems has prepared this “reboot” of our tips for evaluating “or equal” substitutions to help you navigate the decision-making process when confronted with a proposed alternative geosynthetic product. According to a recent special feature article from Geosynthetic News Alerts (GNA), more oversight and diligence is needed—now more than ever—as deceptive products and inferior raw materials continue to find their way into global markets. According to GNA “Distributors and installers that place orders in good faith—particularly with overseas vendors—may wind up with rolls of geosynthetics they can’t use, and no wriggle room in compressed delivery timelines to find alternatives or otherwise rectify errors.” To protect against this, GNA goes on to emphasize the importance of vetting geosynthetics suppliers to maintain quality metrics. In light of this, Presto offers this reboot of our five tips for evaluating “or equal” substitutions to help you keep your project on the path to success amidst the chaos.

Tip #1: Review Product Datasheets Closely (Be Wary of Disclaimers)

Many design professionals tend to focus on the numbers shown on a product datasheet and may even have an implicit trust in the information provided. Unfortunately, some geosynthetics manufacturers and distributors will use this to their advantage. After an initial review of the product data, you will have a sense of whether the product at least appears to meet the project specs on the surface. However, it is imperative to dig a little deeper. Pay close attention to any disclaimer language in the fine print at the bottom of the page. Disclaimers that include statements such as “…specifications may change without notice” are a red flag. Manufacturers who invest in quality assurance programs typically don’t need to provide this type of disclaimer, and are willing to stand behind their published product data.

geocell disclaimer warningTip #2: Learn More About the Product Manufacturer

Starting with a few simple questions, you can obtain a sense of whether or not the product is “tried-and-true,” relatively new, or entirely unproven. Below are a few questions that can help you learn more.

  • Who actually manufacturers the product? This is particularly important when working with organizations that claim to be both a distributor and manufacturer of geosynthetics products. It is important to understand specifically which products they make versus those they distribute or offer under private label agreements (or OEM license agreements). Most importantly, remember that just because a company’s logo is on a product datasheet does not mean they are the manufacturer. Only accept product datasheets with the manufacturer’s information on it—not the distributor!
  • Can the manufacturer provide project references or case studies demonstrating the proposed substitution has been successfully used on similar projects elsewhere?
  • Can the manufacturer provide calculations demonstrating the proposed alternative will meet design objectives?
  • Can the manufacturer provide technical assistance during installation and provide support if unexpected challenges should arise during construction?

Tip #3: Look for Markings of Product Quality & Manufacturer Integrity

Indications of product quality such as the CE marking and ISO certification are useful in establishing an increased level of confidence that the manufacturer holds product quality and data integrity in high regard.

  • CE Mark – The CE Mark is an EU-mandated regulatory mark declaring the manufacturer’s product data is trustworthy and must be carried on products sold in the European market. While not required for geosynthetic products sold outside of the EU, it can provide a quick “gut check” as less reputable manufacturers will have difficulty obtaining this mark. The CE mark should include the number of the certification body beneath it, and the manufacturer should be able to provide a valid Certificate of Conformity of Factory Production Control upon request. The CE certificate will identify which products are included, as well as the location where the products were manufactured.
  • ISO 9001 Certification – For a manufacturer, obtaining certification under the ISO 9001 standard requires a significant commitment (and investment) in establishing and maintaining a comprehensive quality management program. Comprised of quality management procedures (QMPs), the program must consider every step of the production process, from the receipt and handling of raw materials to the finished product. Manufacturers who are ISO-certified should be able to provide a valid Certificate of Registration upon request. The ISO certificate will identify the name of the manufacturer, certificate number, certifying body, and a statement indicating the manufacturer’s quality management system complies with the requirements of ISO 9001 for the specific products of interest.
  • Certificate of Analysis (COA) – Implementing a robust ISO-certified quality management program typically requires continuous quality assurance and quality control testing in order for produced goods to be approved for release from the manufacturing facility. As part of this testing, a Certificate of Analysis, or COA, should be available for all manufactured lot numbers. Accordingly, reputable geosynthetics manufacturers should be able to provide COAs for products that ship to your project site, thereby providing documentation that the goods received were tested and approved in accordance with their ISO-certified quality management program.

Tip #4: Get Third-Party Data

This typically begins with a request to the contractor or manufacturer to provide third-party data to confirm the results are consistent with the product datasheet, and that the proposed substitution will perform as advertised. With manufacturer-provided data, it is important to verify that the results are from an accredited third-party laboratory. If you are not comfortable with the data provided, or have lingering doubts, request that the contractor provide representative samples of the material for further inspection and testing. Provided the project budget allows, an ideal laboratory test program would include analysis of the samples of the proposed substitution as well as the originally-specified product. Including the originally-specified product as the baseline for comparison allows for a comprehensive evaluation of the results, and ultimately supports in making a well-informed decision.

Tip #5: Prepare a Summary of Your Evaluation

Before responding to project stakeholders, it can be helpful to prepare a summary of your evaluation laying out your findings and providing the rationale behind your assessment. We’ve prepared a checklist and product scoring sheet incorporating the considerations above that can be used as a starting point for completing your evaluation. You can download this form using the link below.

Download the Checklist >>


Read “The Significance of High-Quality Standards” >>

How Geosynthetics Are Uniquely Poised to Help Alleviate Congestion at U.S. Ports

Written by: Michael J. Dickey, PE, Director and Bryan Wedin, PE, Chief Design Engineer

On May 6, 2022, the Maritime Administration (MARAD) released an amended Notice of Funding Opportunity (NOFO), allocating over $234 million for port infrastructure development in 2022. Adding to the previously appropriated amount of $450 million from the Infrastructure Investment and Jobs Act (IIJA, or Bipartisan Infrastructure Law), this will bring the total amount available for port improvement projects to $684 million for FY2022.

The significance of this investment comes at a crucial time. According to the American Association of Port Authorities, the pandemic has laid bare the need for a transport system that is able to surge and stretch across all links—from sea, to land, to rail, to warehouse, to consumer. The question is, how can this funding be used to meet this need quickly and cost-effectively? The answer may lie in a strategy implemented in 2021 in the state of Georgia to alleviate congestion at the Port of Savannah. The Georgia Port Authority, in partnership with Norfolk Southern, implemented a solution that has caught the attention of other U.S. port authorities and Class I railroads using what is being referred to as “pop-up container yards”.

What Is a Pop-Up Container Yard?

In a recent article featured on Freightwaves.com, pop-up container yards are described as “mini-versions of inland ports where containers are brought to strategically located sites by intermodal rail, shortening the distance trucks have to travel to collect imports or drop off exports and reducing traffic in and around busy seaports. The concept essentially brings the seaport closer to manufacturing, agriculture and population centers.” While, on the surface, pop-up container yards may seem like a very pragmatic solution to a complex problem, developing one of these sites can come with its own set of unique challenges.

container yard

One such challenge relates to existing ground conditions. From a geotechnical perspective, the ground conditions may not be suitable for the heavy demands of container handling and storage operations. And unless an alternate location has been identified that is better suited, project engineers and designers must often evaluate the need for ground improvement options capable of supporting heavy vehicle loads over soft or unstable soils. The good news is that the GEOWEB® Soil Stabilization System was invented specifically for this purpose. The GEOWEB Cellular Confinement System (CCS) is an American-made geosynthetic product manufactured by Presto Geosystems that has been in use for over forty years.

GEOWEB Geocells Improve Bearing Capacity Over Soft or Unstable Soils 

Created through a collaboration between the U.S. Army Corps of Engineers (USACE) and Presto Products Co., the GEOWEB system was designed to address the needs of the U.S. military to build access roads capable of supporting heavy vehicle loads over soft or unstable soils. The system’s deep cellular network controls both the horizontal and vertical movement of unstable base soils. In load-support applications, when a static or dynamic load is applied to a geocell-reinforced layer, lateral earth pressures are mobilized and transferred across a three-dimensional network of interconnected cells. The layer essentially performs like a composite material, facilitating a phenomenon known as the mattress effect.

Success Story: CSX Intermodal Facility in Charleston

The CSX Charleston Intermodal Yard required base reinforcement due to poor and unstable subgrade conditions. Shallow surficial soils comprised very loose sandy soils that were inadequate to support the operation of reach stackers used in regular lifting and moving containers. In addition, a similar condition was prevalent in another area of the site designated for chassis parking. Both areas were prone to significant rutting due to the inherent instability of shallow surficial soils.

The Presto Geosystems’ design staff worked closely with CSX to provide design recommendations based on sub base strength, vehicle loadings, and frequency of traffic. After a thorough review of the geotechnical report, it was determined that on-site material could be beneficially reused as infill in the GEOWEB system.

Eliminating the need to import costly aggregate and structural fill led to significant cost savings, and yard downtime was substantially reduced. Minimizing downtime was especially important due to the high volume of tractor-trailers the facility handles daily. The reach stacker area used an enhanced woven geotextile, three-inch base, six-inch GEOWEB panels, and a three-inch wearing surface. The chassis parking area utilized a high-strength woven geotextile, six-inch GEOWEB panels, and a two-inch wearing surface. The GEOWEB system stabilized a total of 1.75 acres. Both areas have required minimal maintenance and continue to function as designed. Both areas have required minimal maintenance and continue to function as designed.

Protect Your Project Schedule and Reduce Costs with GEOWEB® Geocells

geoweb base reduction

As demonstrated by the success at the CSX intermodal facility, where a suitable source of clean sand is available, the GEOWEB cells can be infilled with on-site material in place of expensive aggregate, drastically reducing imported aggregate volumes altogether. Even at sites where a suitable source of clean sand is not readily available, geocells offer the potential to reduce the required thickness of the base layer in a load support application by as much as 50%. In both cases, project stakeholders can realize cost savings, as well as a potential reduction of schedule-related risks, particularly where the availability of suitable aggregate, or availability of truck drivers to transport said material, might otherwise be outside of the project decision-maker’s control.

Compared to planar geosynthetic products such as geogrids—which commonly rely on expensive, imported high-quality aggregate—geocells are highly versatile and can be filled with a variety of commonly available and economical infill options. Infill options include sand, crushed aggregate, recycled concrete, pulverized debris, recycled asphalt, or other locally sourced materials. The illustration below provides a comparison of four structurally equivalent aggregate sections over a subgrade with a CBR of 0.5%.

As illustrated, the unreinforced aggregate option would require more than 36 inches of aggregate to achieve minimal stability, and the planar geosynthetic option (geogrid + geotextile) would require 26 inches of aggregate. In contrast, the GEOWEB geocells reduce the total section thickness to only 15 inches, and where suitable on-site material (OSM) is available, it is possible to limit imported aggregate to just the wearing course.  

A Value-Engineered Solution for Your Pop-Up Container Yard Project

The GEOWEB geocells can be added to pop-up container yard projects to provide a value-engineered solution for both paved and unpaved areas. This not only reduces construction costs, but can also help keep your project on track when aggregate shortages and limited availability of truck drivers threaten your project schedule.

Project-specific recommendations are influenced by loading, subgrade soils, traffic frequency, and infill type. The engineering team at Presto Geosystems works closely with engineers and project planners, offering free project evaluation services and on-site installation support. Our recommendations will deliver a technically sound, cost-effective solution based on over four decades of accredited research and testing data. Please contact our knowledgeable staff and network of qualified distributors and representatives to discuss your project needs today.

Contact: Bryan Wedin, PE, Chief Design Engineer

Dam Structure Safety Installation and Repair Using Advanced Geosynthetic Technology

Written By: Samantha Justice, P.E.

damDams and Spillways Are a Critical Part of U.S. Infrastructure

With estimates of 84,000 structures nationwide, dams and spillways are essential for controlling flooding, water distribution and management, and providing hydroelectric power. Unfortunately, these structures cannot last forever. The average age of dams and spillways in the US is 57 years, seven years over the typical 50-year lifespan of these structures. Aging infrastructure can lead to serious consequences if safety precautions are not taken, or measures are not implemented to address identified problems in a timely manner. The most important measure that any dam manager can apply is continual inspection and upkeep.

The US Army Corps of Engineers Infrastructure Report Card rating for 2021 was a C-, and the health of dam structures was a significant part of that low rating. State and federal regulations provide a framework for the assessment and maintenance of dam and spillway structures-at a minimum yearly audit inspections that identify areas that need repair or replacement are required. Performing these repairs can help extend the lifetime of dams to help keep essential services in place without excessive cost or increased failure potential.

Understanding Areas of Concern for Existing Structures

The vast majority of America’s rivers and lakes have existing dams and spillways, and as such, very few new structures are being built. With new construction, safety measures can be incorporated during the design phase to extend the lifetime of the project and help prevent failures. The true threat is with existing structures that have gone past their intended lifetimes or have seen areas of potential failure.

A recent example of the potential for catastrophic damage due to a dam failure is the 2017 Oroville Dam crisis in Northern California. Extremely heavy rainfall over a number of days raised the level of Lake Oroville, increasing the flow over the main spillway to above-average levels.  Almost immediately, damage was observed in the lower half of the spillway, with a large section of the concrete path collapsing. The emergency spillway was utilized to help prevent further damage to the main spillway, however, excessive erosion occurred to the emergency spillway path, and emergency repairs were subsequently required to address damage in both spillway areas. Further damage occurred when more rainfall increased the lake level yet again, including blocking the downstream river and requiring the immediate shutdown of the Oroville hydroelectric power plant. Luckily, total collapse of the dam did not occur, but more than 180,000 residents of the Feather River Basin were required to evacuate for multiple days, and over the next year, more than 1,000 people worked more than 2 million hours to rebuild the spillways to ensure the safety of downstream communities.

With the passage of the 2021 Infrastructure Investment and Jobs Act, states will have access to funds to complete repairs and upgrades of aging dams and spillways before failure can occur. The failure at the Oroville Dam was preceded by rejection of a 2005 upgrade proposal to build a concrete emergency spillway that could have handled the high water flows seen in the 2017 event. Re-evaluating existing structures to ensure that they are still able to withstand 100-year and 500-year flood events is crucial to the longevity of the dam network within the US. Maintaining both upstream and downstream dam faces and spillways is an ongoing process, fighting against wave action and erosion, as well as any potential impact damage caused during storm events. Even simple maintenance of roads and work pads over dams can have a lasting effect on the health of these structures by allowing workers access to inspect and repair the structures quickly and easily.

GEOWEB® Geocells Are a Repair Solution for Dams and Spillway Sites

GEOWEB geocell technology is a versatile geosynthetic system that can be used to create long-term solutions for many of the common dam and spillway problem areas. Geocells function as the support structure for unpaved roadways, capable of supporting maintenance and repair vehicles. They also function as surface erosion control solutions, preventing the formation of rills or the collapse of unstable soils due to water flow, wave action, and storm events.

charleroi dam geocells

Charleroi Dam

 

GEOWEB geocells can be placed on the upstream face of a dam structure to mitigate the effects of wave action on the dam, supporting existing riprap areas, or replacing them entirely with vegetation, gravel or concrete. The flexibility of the GEOWEB system allows for the use of mixed infill materials, such as topsoil above normal water levels for grass growth and small aggregate below the water level for erosion prevention. Comprised of high-density polyethylene (HDPE), GEOWEB geocells are formulated for long term durability to resist weathering, chemical attack, and ultraviolet radiation, and are therefore suitable for use in applications where the material will be subjected to cyclic wetting and drying, permanently submerged, or full sun exposure. The material is not prone to degradation or corrosion due to environmental factors, and can be placed on the downstream face of, or within, a spillway structure. The system is also compatible with concrete infill to accommodate extremely high flow velocities. For comparison, Table 1 summarizes allowable velocities and shear stresses for various channel lining alternatives.

 Comparison of allowable velocity and shear stress for channel lining alternatives

In emergency spillway areas, topsoil infill with vegetation can be used to allow for a natural camouflaged look, while still preventing erosion and uncontrolled water flow, and outperforming traditional unreinforced channel lining alternatives.

Staging areas and maintenance roads are also integral parts of a dam site, and when necessary, these features provide vital access and adequate ground support for vehicles and heavy equipment to perform inspections, routine maintenance, and repairs. The GEOWEB system can be used in a variety of load support applications, including unpaved access roads, laydown areas, and parking lots. Reinforcing these roads means significantly reduced maintenance requirements, reduced rutting, and access to areas that might otherwise be unable to support heavy loads due to soft soil conditions. Minimizing stresses on top of dam structures is critically important to preventing the formation of cracks or slumps within the structure that could lead to failure. The GEOWEB road system can be integrated with the slope protection system on the upstream and downstream faces of the dam for a continuously protected berm from water, vehicle, and impact loads.

mud lake dam geocells

Mud Lake Dam

Design Support & Resources for the GEOWEB System Applications

The engineering team at Presto Geosystems works closely with engineers and project planners, offering free project evaluation services and on-site support. Our recommendations will deliver a technically sound, cost-effective solution based on four decades of accredited research and testing data. Please contact our knowledgeable staff and network of qualified distributors and representatives to discuss your project needs today.

Related Articles and Case Studies

Mud Lake Dam Rehabilitation
Olivenhain Dam Power Line Access

References

United States Department of Agriculture, Natural Resources Conservation Service, (2007) Part 654 Stream Restoration Design, National Engineering Handbook, Chapter 8, Threshold Channel Design, (viewed 23 March 2022 and available https://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=17784.wba as a link directly to Chapter 8). Table 8-11 “Allowable velocity and shear stress for selected lining materials” referenced from 8-37.

Colorado State University, Engineering Research Center (2009) Hydraulic Testing and Data Report for GEOWEB 30v with Concrete, research summary courtesy Presto Geosystems, (viewed 23 March 2022 and available Colorado State University Testing PDF)

Sustainable Vegetated Channels = The Death of Rip Rap

Rip rap is a common channel protection method because of its resistance to most flows with appropriate rock size; however, it does have significant drawbacks. Material can be expensive, not locally available, and placement requires heavy equipment. Additionally, rip rap channels are prone to regular maintenance, collection of debris and garbage, erosion at boundaries, undermining, and movement.

Naturally vegetated channels are grassed greenways that offer substantially lower maintenance and cost but are limited in their ability to resist moderate-high flows and shear forces even for short durations—unless the soils and vegetation can be stabilized.

High-Performing Vegetated Solution

The GEOWEB® Soil Confinement System offers protection to channels with continuous low flows—as well as moderate-to-high flow intermittent channels. The system’s honeycomb-like network creates check-dams that protect the soil layer from hydrological erosive forces and resulting erosion that impacts unconfined soils. Cell wall perforations lock up with the vegetative root for further stabilization.

The GEOWEB single-layer vegetated channels can withstand ~9 ft/s (2.7 m/s), more than doubling the resistance of typical unsupported vegetated channels (4 ft/s (1.2 m/s). The GEOWEB channels can withstand even higher velocities—as high as 30 ft/s (9m/s)—with an overlying Turf Reinforcement Mat (TRM) when fully vegetated. This is a significant improvement, essentially doubling performance resistance to shear stress and velocities for TRMs and Erosion Control Blankets (ECBs). Rigorous flume testing at Colorado State University (CSU) with varying shear stresses and flow rates substantiated resistance of high shear stresses up to 15.9 lbf/ft2 (77.6 kgf/m2).

Vegetated GEOWEB TRM System Compared to Rip Rap

The GEOWEB TRM System offers advantages over rip rap for vegetated channels:

  • Streamlined Transition with Boundaries: Smooth integration with boundaries reduces undermining and erosion at boundary points
  • Higher Permeability: Ideal for environmentally low-impact design
  • Easier Integration in Landscape Plan: Less obtrusive and can be incorporated as a “soft” solution (i.e., grassed conveyances) with capabilities of some hard-armored systems

Sustainable Solution for Vegetated Conveyances

Sustainable vegetation in channels can be achieved with the GEOWEB TRM system. Applications that benefit include roadside ditches, stormwater channels, shoreline embankments, dams, spillways, and pond overflow systems. The GEOWEB/TRM system is a more sustainable—and environmentally friendly solution than rip rap for these common applications.

 

 

 

Presto offers full design and specification tools and a free project evaluation service to determine applicability.

Meet the Presto Geosystems Team: Get to Know JP

meet JP imageWe have a great team here at Presto Geosystems, so we thought it would be fun to share a bit more about each member through a new blog series. For our inaugural Meet the Presto Geosystems Team blog post, we are thrilled to introduce José Pablo George—Presto Geosystem’s International Business Manager (BDM).

Let’s get to know JP…

JP

How long have you been with Presto Geosystems?

Time slides and blurs in a funny way. It seems so natural for me to be doing what I do with GEO, as if I’ve always been here and can draw deeply on decades of experiences, yet at the same time I still have the positive outlook and optimism of a freshly minted graduate. The year-over-year calendar and the bits of chrome in my hair suggest a compromise: this year marks my eighth year with GEO; call me a well-seasoned new-ish guy.

Can you tell us a bit about your background?

My specialty is in establishing, culturing, and maintaining business relationships, especially with our international clients. My former life and experiences pre-Presto support this well.

I was a Spanish teacher (secondary schools and technical colleges) for 17 years, and have the linguistic skills and cross-cultural skills thanks to that, as well as the “educating adults” part needed for onboarding new network agents for us. Presto initially hired me as a LATAM BDM, and I gradually took over most of the international world from there!

I´ve developed my chops with quality assurance and network training through the State of WI DOT, technical colleges, and Harley-Davidson corporate in their Quality Assurance programs and motorcycle training programs. I´ve studied Verbal Judo, am a legit Black Belt in Tae Kwon Do, and have negotiated labor-management bargaining contracts from both sides of the table. I don´t shy away from tough conversations, and although I´m usually the “quiet one,” my words have strength and I usually deliver them in a way to make them count.

Additional life experiences of growing up with my artist grandfather, working the family dairy farm, building houses from blueprints, solo motorcycle trips across the country, living and working abroad, and working the world´s most famous pottery kilns have all expanded my perspective, and make for interesting stories to share (another time).

What attracted you to the world of geosynthetics?

Initially it was softball and Spanish that attracted me to the world of geosynthetics. The former Geosystems Director and I played on a rec league softball team, and he kept trying to hire me for my Spanish skills. When two other Fortune 500 companies offered me positions (also due to my Spanish skills), I figured a career change merited a closer look. I decided to leave teaching for the corporate world, and am glad to have made the leap. Since starting with Presto, I have obtained my CPESC certification and have learned so much more about geosynthetics and engineered soil stabilization solutions. I´m even published and on patents now!

What does your job entail? Can you take us through a day in the life as an International Man of Myst…umm, I mean International Business Manager?

The day of an International Manager is always a mystery… yet also contains some comfortable stability. Every single day I am talking with contacts from around the globe. My mobile number is my WhatsApp, Viber, Signal, Teams, text, and Messenger number… and I use each of them to reach our agents and clients in the way that is most natural to them. Every day I get to use my Spanish language skills, and I have also learned a bit of Dutch, Setswana, Japanese, Portuguese, French, and German. Most days I am offering design and sales support, sourcing appropriate supporting resources for projects, and doing my part to keep our solutions present in the minds of engineers and clients. Most weeks I am presenting the details of one of our solution sets for a particular application, such as Infrastructure Resilience for Roads and Bridges, Channel Armoring, or Mine Slope Reclamation… sometimes in English, sometimes in Spanish.  Sometimes it means presentations… of whitepapers… to government entities… to International Erosion Control or Geosynthetics groups, and the like. Once upon a time, my job meant lots of travel to meet with clients IRL, not just virtually. I look forward to the travel again someday. Really, my job entails building relationships with the right connections. Sometimes I have to seek them out, sometimes connections find us. Either way, I must develop them into something.

What do you like most about your job and/or what do you like most about this industry?

What I like most about my job is the connection to people and places around the globe. The industry allows me to offer lasting, valuable solutions to real problems. We solve the most challenging soil stabilization problems, and give the world a strong foundation to build on. There is a bit of superhero stuff in that! What´s not to like?

Can you tell us a little about what it’s like working with international business partners?

Ha! Never before have I understood time zone differences and ultra-long project gestation times so well.  I organize my day to speak with different parts of the world at different times… Europe and the UK at the start of my day, LATAM and SADC throughout the day, Asia Pacific and MENA towards the end of the day… it is a lovely variety! Not always so clean cut, but that generalizes it some. I must exercise great patience… as anything international involves extra touches and tending. With all of our international projects and partners, it comes back to building and keeping strong relationships, as well as ease of use, reliability, and high performance. Our partners know we will do what it takes, and with integrity, to help them find success.

What do you enjoy doing when you aren’t out helping solve the world’s soil-stabilization and erosion challenges?

I love spending time in the forest, and am fortunate to live in a region that allows me to experience the changing seasons with unhindered access to the woods. My family and I love to camp, hunt, fish, ski, bike, hike, and enjoy time together outdoors. I hate ticks and mosquitoes, and most other things that try to bite me without my permission… but generally speaking will spend as much time as possible in the woods.

What is your favorite place in the world to visit?

There are so very many places I have yet to see!!! How can I pick just one?!

Tops on my list of having been: Cartagena, Colombia; Granada, Nicaragua; La Rioja, Spain; the Frankfurt area of Germany; and the Parque Manuel Antonio in Costa Rica.

Soon-to-be favorites include Paris and the wine country of France, and the Amsterdam area of the Netherlands.

An eventual favorite trip will be a summer camping trip to the Denali area of Alaska… and to Banff, Alberta, Canada. Maybe back to the Patagonia area of Argentina, this time to fish and not just for work… and to other parts of Japan beyond the Tokyo area, including Sapporo, Osaka, and Fukuoka.  So many adventures yet to be had!

If you could meet anyone, living or dead, who would you meet?

This is a tough one. At this juncture in time, if I had to pick just one person I´d like to meet, I would ask Keanu Reeves to accompany me for a long walk and talk at a dog park with our pets. He is also an International Man of Mystery, a “cool breeze over the mountains” that is aware of his celebrity status yet is generous and careful with his presence. I admire the way he sticks to his principles and manages to stay cool and look at the bright side, with kindness, humility, and gratitude. He models being a good human in a way the world needs right now. If Keanu turned me down, I would ask Steve Martin to share his mad banjo skills and a few jokes with my son, or Shakira to sing with my daughter.

What would you name the autobiography of your life?

The Next Adventure Awaits…

JP Book