Using Geosynthetics to Stabilize Soils in a Harsh Environment

Posted January 30, 2024 by Katie Bocskor

By Dhani Narejo, PE, Bruno Hay, and Bryan Wedin, PE

Mine Site Erosion Problems

One of the largest nickel mining sites in the world is located on the South Pacific island of New Caledonia. Due to the size of the mining project and the terrain of the site, significant cut-and-fill work for civil engineering structures was unavoidable.

FIGURE 1: A typical progression of erosion at one of the slopes.

Given the magnitude of the site, the challenge of safeguarding the structures against erosion is formidable. Inaction is not an option due to the sensitive nature of the structures, environmental concerns, and a keen desire by the owners to protect the environment. A typical example of the erosion at the site is the slope in Figure 1. Such slopes require continuous maintenance if the erosion problem is not addressed. In some cases, erosion can cause interruption in the mobility of materials and personnel at the site.

Several erosion-control measures had been successfully used at the site, including riprap and concrete. An alternate erosion control system was desired by the owner that would meet the following objectives:

Be cost-effective,
Require little or no maintenance,
Utilize local labor and materials,
Have a design life exceeding 50 years.

Soil, topography, weather

FIGURE 2: A simple representation of ultrabasic soil profile in the island.

Ultrabasic soils cover about one-third of New Caledonia, where large deposits of nickel are found. Peridotites and serpentines–the parent rocks of these soils–formed 1.5-65 million years ago during the Tertiary period.

The chemical weathering of these rocks over thousands of years and subsequent erosion have resulted in a soil formation of the general nature shown in Figure 2. Ultrabasic soils are rich in iron and magnesium, yet are deficient in nutrients to support vegetation. These soils are fragile in structure and easily erodible, especially when the dense vegetation at the surface is disturbed by fires, mining, or construction activities.

The topography of the site is generally hilly and mountainous. Slopes vary continuously from steep to gentle and from fully vegetated to barren. There are numerous water runoff features on the island. There are large areas of unstable soils and mass movement as shown in Figure 2. As a result, soil erosion is a challenging engineering problem in this region.

The weather pattern is cyclonic, with a single cyclone dumping up to 800mm (31 in.) of rain within 24 hours. Significant rainfall from at least three major events has affected the island during the past 50 years.

Tropical Cyclone Anne dropped 714mm (28 in.) of rain within 24 hours in 1988. In 1969, Tropical Cyclone Colleen recorded 214mm (8 in.) of rain in 4 hours. In January 2011, Tropical Cyclone Vania brought a rainfall of 50mm (2 in.) per hour for several hours. The rainfall intensity for a 6-hour, 100-year storm is on the order of 400mm (16 in.) in this region. The annual number of cyclones can range from 2-10.

Table 1 presents the 10 wettest storms recorded on the island (through 2010).

The unstable nature of the soils, together with the hilly terrain and cyclonic weather, presented unique engineering challenges for the soil erosion problems.

Sustainable Solutions

FIGURE 3: Gravel used as the infill in the geocell

The contractor, having installed liner systems at the site, maintained a long and successful relationship with the mining company and was well aware of the challenges associated with protecting the slopes from erosion in this environment.

The owner suggested the potential of geocell applications to develop a conceptual solution to the erosion problems. The solution involved covering the slopes with geocells, three-dimensional structures made of high-density polyethylene (HDPE), designed to contain and stabilize infill material.

The recommended infill material consisted of a byproduct waste aggregate from the mining operation. A nonwoven, needle-punched (NW-NP) geotextile separation layer was also recommended. Figures 3 and 4 present the proposed gravel infill and the geocell, respectively.

FIGURE 4: Expanded and connected geocell sections partially infilled

The owner accepted the contractor’s proposed solution as a more cost-effective answer than previous methods. The geosynthetic solution would require little to no maintenance during the effective design life and was visually appealing.

The proposed gravel infill was available as a waste material at no cost. The installation could be performed by local labor with little technical support and training by the manufacturer. However, the owner required that an independent design engineer prepare a design for the proposed solution.

The primary design considerations included:

Minimum thickness of the geocell,
Veneer stability,
Type of the separation geotextile,
Hydraulic response during a storm, and
Infill procedures.

Due to length constraints for this article, only the thickness and veneer stability are discussed here. Important design conditions for the site related to thickness and veneer stability included:

A maximum slope angle of 45 degrees,
A 6-hour probable maximum precipitation of 39mm (1.5 in.),
A Maximum slope length of 20m (65.5 ft), and
Presence of clay soils.

The geocell thickness was the most challenging factor during the design phase because of the long slope lengths and steep angles. As the thickness of the geocell increased, the driving force due to the infill weight increased, which led to higher anchorage requirements.

Alternatively, as the geocell thickness was decreased, more water could penetrate the clay soil, which could potentially jeopardize the effectiveness of the geocell system. After a detailed analysis, a geocell thickness of 100mm (4 in.) was selected to provide effective coverage and minimize anchorage requirements.

The anchorage requirements are explained with this veneer stability equation:

Where FS = factor of safety against veneer instability, C_r = required anchorage (kPa), h = thickness of the geocell (m), β = slope angle (degrees), δ = geotextile-subgrade friction angle (degrees).

A factor of safety of 1.4 was used, which is typical for slope stability analysis. The friction angle between the geotextile and underlaying site clay was base on GRI Report #30 (Koerner and Narejo, 2005). Figure 5 provides the relevant figure from this report.

A friction angle of 28 degrees was used in the calculations. Density of gravel, γ, was 20 kN/m³. Slope angle, β, varied from 26-45 degrees. The required anchorage, C_r, depends on the slope angle β for the known or assumed values of FS, h, δ, and γ. For the β value of 45 degrees, the required anchorage is 1.2 kN/m².

FIGURE 5: Historical data for geotextile-clay shear strength (Koerner & Narejo, 2005)

The concept is simple and is based on the soil containment function of the geocell and the separation function of the geotextile.

For geocell installations, two anchorage methods that include stakes and tendons are typically evaluated. In the design phase, galvanized No. 4 rebar provided the most cost-effective solution. The rebar spacing was determined based on actual site load tests. Fifteen locations were identified for the field load tests. The rebar intended for use was hammered into the slope and a downward pull load was applied parallel to the slope. The load was increased until either maximum load capacity was reached or the rebar broke or pulled out of the ground. Testing determined that a maximum anchorage of 100kg or 0.98kN could be used for a single rebar anchor. From this value, the spacing of the stakes was determined.

Installation

FIGURE 6: Installation of the geocell in progress

The contractor recontoured the slopes where there was significant damage caused by erosion. A 6oz. NW-NP geotextile was installed on the slope as a separation layer between the existing subgrade layer and the gravel infill material. Cellular confinement sections were installed over the geotextile.

Starting from the top of the slope, the sections were expanded down the slope and filled with waste aggregate (Figure 6). The installation was completed within the target time.

Performance

In 2011, just weeks after the completion of the first phase of the project, Tropical Cyclone Vania dropped a total of more than 600mm (24in.) of rain within a 24-hour period. The site was further affected when, within 24 hours of Vania’s impact, a magnitude-7 earthquake hit a nearby island. This was a real-life test for a geocell installation on steep slopes, some up to 45 degrees.

The slope coverage performed as designed, with little or no erosion even on the steepest of the slopes. These successes were in keeping with previous results experienced by the manufacturer’s customers around the Pacific Rim—that the cellular confinement performs consistently under wet and seismic conditions.

Project Summary

For difficult and complex site conditions, cellular confinement applications can provide powerful protection against soil erosion.

The concept is simple and is based on the soil-containment function of the geocell and the separation function of the geotextile. A thin layer of overburden soil contained within the cell is enough to protect unstable slopes.

This protection is possible even on steep slopes if proper engineering procedures are followed and, most critically, provided that engineering design solutions are used only for the specific material and manufacturing characteristics of a cellular confinement material.

The engineer’s experience with the proposed design solution, that of the contractor with the site, and that of the manufacturer with previous projects in the region all contributed to the project’s success. The decision to use waste material as the infill during the design phase was crucial and limited project costs.

The materials installed on the initial phases of the slopes have already experienced dozens of heavy rainfalls and at lease one earthquake. This case history shows how geosynthetics can be engineered to solve complex problems at a significantly lower cost when compared to traditional solutions.

References: George Koerner and Dhani Narejo, “Direct Shear Database of Geosynthetic-to-Geosynthetic and Geosynthetic-to-Soil Interfaces,” Geosynthetics Research Institute, GRI Report #30, June 14, 2005.

Dhani Narejo, P.E., Principal at Care Engineering LLC in Conroe, Texas is a member of Geosynthetics Magazine’s Editorial Advisory Committee.

Bruno Hay, is Business Manager at FLI Pacifique SNC in New Caledonia.

Bryan Wedin, P.E., is Chief Civil Engineer with Presto Geosystems in Appleton, Wisconsin.

The Dangers of Breaking Specs and Bid Shopping

Posted December 28, 2023 by Ashley Beyer

Written by Sam Justice, P.E.

Building roads, housing, and other critical infrastructure is a great responsibility taken on by engineers, architects and project owners. Ensuring that these structures are safe and reliable for years and decades is of the utmost importance at all stages of design and construction.

The Challenge of Maintaining Quality in Construction

The design team creates building plans and the associated specification that capture the essence of their vision as they work to write the guiding documents for their project. They make decisions about product types, grades, and take great pains to build into their documents citations of certifications and standards to assure only quality materials are allowed on the site.

However, product competition and budget demands are a concern seen in many projects that can challenge the specifications intended to produce the best possible structure. Substandard “or equal” substitutions can be encountered in the critical moments between design, bid awards, and construction. It is up to the specifying engineers and architects to hold their spec in all phases of the process to ensure the right materials and installation procedures are used.

The Bidding Process and Material Selection

Contractors often produce bids with the materials indicated by the project engineers, but with a critical eye on material and labor costs. Soon after the bid opening or notice of award, bid shopping for “or equal” materials is expected. Bid shopping on publicly-funded projects is disallowed by legislation in some localities, but even when formally disallowed, informally it occurs widely.

The Risks of Specification-Slide

It is common for professional engineers and architects to accept substitutions requested by contractors without full due diligence because of pressures from time constraints, cost overruns, and pressure from contractors to avoid unfamiliar products. This “specification-slide” is not intentional by the design team, but is often an explicit feature of knock-off providers who join the game with inferior products that do not exactly meet the specification, but are promoted as equals. Without intimate knowledge of a product that may be new to a professional, they may not know the factors that make difference between a genuine product and an inferior material specification.

The Importance of Accurate Material Specifications in Complex Projects

Close enough may be acceptable for some sites, but when you consider complex and critical civil works projects, the differences in design strength and performance could be the difference between success and failure. There may also be components of the complete “system” solution (e.g. connectors, load transfer devices or customized accessories) that contribute significantly to the design strength and speed of installation that all providers cannot provide. These copycat providers simply jury rig together their version or ignore appurtenances altogether yet still offer the cobbled together system as an equal.

Addressing Failures and Upholding Standards

When the “or equal” product fails during installation, or worse, during service, results can range from minor to catastrophic. Perhaps the fix is as simple as requiring the contractor to stay onsite longer to install the genuine specified material, or perhaps the consequence is as bad as roadway failing while being driven on or erosion impacting infrastructure downslope, with loss of service, repair or replacement of roads, rails, or building, or potentially direct impact to people. Contractors lose money and time, engineers or architects lose reputation, and project owners have the consequences of those failure on hand.

Pay attention to the materials and products specified, and ensure that they meet the necessary standards, with no concerning disclaimers or fine print. Deliver certainty and build with materials that can be trusted. Hold the specification to the right materials, through all stages, every time.

Why Geocells Outperform Geogrids for Road Construction

Posted November 13, 2023 by Katie Bocskor

Geocells (cellular confinement system CCS) 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.

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: Diagram It 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.

Geosynthetics and PFAS: Understanding the Role of Polymer Processing Aids in Geosynthetics

Posted November 8, 2023 by Katie Bocskor

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

Like many other industries, geosynthetics manufacturers are navigating the rapidly evolving landscape of new per- and polyfluoroalkyl substances (PFAS) regulations. However, in the case of geosynthetic products, an interesting and seemingly paradoxical question emerges: Is it possible that the same products that have been designed to solve complex environmental problems, and even contain pollutants, could also be a possible contributing source of PFAS?

In this article, we explore this question and discuss the historic role of polymer processing aids (PPAs) in the production of geosynthetics.

What Does Intentionally vs Unintentionally Added PFAS Mean?

Since the discovery of PFAS in the 1930s, these compounds have been widely used in manufacturing operations worldwide—both intentionally and unintentionally. In a recent article published by the American Bar Association, the concept of intentional versus unintentional use of PFAS is discussed, and in the case of the latter, the use of fluorinated PPAS used in thermoplastics processing is highlighted as a well-known unintentional PFAS source. How this concept relates to traditional geosynthetics manufacturing is discussed further below.

Eliminating Polymer Processing Aids (PPAs) from Geosynthetics

Production of geosynthetic products such as geogrids, geomembranes, and geocells commonly involves sheet extrusion of raw materials as an initial step in the manufacturing process. The raw materials typically comprise various pelletized thermoplastic materials (e.g., polyethylene, polypropylene, etc.) that have been engineered by resin suppliers and plastics compounders to incorporate ingredients for improved processability. To achieve this, additives known as polymer processing aids (PPAs) are incorporated into the raw materials. PPAs may be incorporated into the base resin materials, additives, or “master batches,” in different proprietary formulations intended to meet manufacturers’ needs. Up until recently, fluorinated PPAs, a potential source of PFAS, were the go-to standard for PPAs.

By incorporating PPAs into the raw materials, faster extrusion speeds can be achieved without increasing resin processing temperatures, thereby limiting energy consumption and reducing operating costs. Additionally, in the case of products where a smooth finish may be required, such as smooth geomembrane liners, PPAs eliminate “melt fracture,” a phenomenon caused by excessive shear stress on the molten resin that leads to undesirable roughness in the finished product.

Accordingly, with increased awareness of the potential presence of integral fluorinated PPAs in raw materials, many geosynthetics manufacturers are proactively conducting due diligence efforts of their own to identify and eliminate fluorinated PPAs from their products. This entails vetting of raw materials to ensure no product ingredients contain added PFAS from suppliers, and where necessary, adjusting product formulations to eliminate PFAS-containing ingredients.

Presto Geosystems, world-leading geocell manufacturer and inventor of the GEOWEB® Cellular Confinement System (CCS), recently conducted similar efforts, and confirms the product formulation for GEOWEB Geocells does not contain any intentionally added per- and polyfluoroalkyl substances (PFAS), and based on this understanding, GEOWEB Geocells are not expected to pose a risk of release of PFAS compounds into the environment.

Therefore, in returning to the original question, could geosynthetics be a possible contributing source of PFAS to the environment? The answer is yes…maybe. Engineers and project owners are encouraged to do their own due diligence when exploring different geosynthetics products, and when necessary, obtain a written statement from the manufacturer confirming they have conducted due diligence to confirm their products do not contain any intentionally added PFAS, and are therefore not expected to pose a risk of release of PFAS compounds into the environment.

Meet the Presto Geosystems Team: Get to Know Lauren

Posted October 30, 2023 by Ashley Beyer

Meet Lauren Armstrong, the newest member at Presto Geosystems, who joined the team in August 2023. Hailing from a small town near Chicago, Lauren has had quite the career journey. She began her career in IT in downtown Chicago, later transitioning to the Fiberglass Reinforced Plastic (FRP) industry, with her persistent passion for business development guiding her every step. Now at Presto Geosystems, she’s learning all about geosynthetics and facing new challenges head-on. Join Lauren as she shares insights from her past experiences, aspirations for the future, and the path that led her to Presto Geosystems.

How long have you been with Presto Geosystems?

I am pretty new to the crew—I started at Presto Geosystems in August 2023.

Can you tell us a bit about your background?

I have lived in a small town that is about 50 miles southwest of Chicago for my entire life. While it may not be the most exciting place in the world, I can’t imagine living anywhere else. I attended the University of Illinois at Urbana-Champaign and graduated with a degree in Marketing.

My first job out of college was in downtown Chicago at an IT company working as an Account Manager. The idea of working in the big city was very exciting as a newly college graduate; however, I failed to realize this would mean I would have to commute a total of four hours a day getting to and from downtown. Six months after I started, I got stuck on the highway for over five hours due to a bad ice storm while attempting to make it to work. Once I was finally able to loop around, I returned home feeling so defeated. About 10 minutes after I got home, an HR manager for a company I had interviewed with that prior summer called because they had a job opening (15 minutes from my house, might I add) and asked if I would be interested. The timing of this call could not have been more impeccable. I enthusiastically responded with a “YES!” and moved on to my next journey.

For the next six years, I worked for a company that manufactures Fiberglass Reinforced Plastic (FRP) wall paneling, as well as the siding and roofing for RVs and semi-trucks. For those of you that do not know what FRP is—it is the white wall panels with a bumpy texture that you typically see in restaurant kitchens, janitor closets, restrooms, etc. While here, I was able to gain experience in account management, customer service and inside sales; however, the most recent position I held while here was Lead Generation Coordinator. In this role, I would follow up on inbound leads, as well as utilize various sales tools and market research to identify potential projects where FRP could be installed. I worked with architects and contractors to get our products specified on projects, as well as assisted the sales team to help win opportunities. The role gave me great experience and helped me get to where I am today.

What led you to a career in business development and how did you come to join Presto Geosystems?

Earlier this year, I decided I was ready to embark on a new adventure in terms of my career, which is what eventually led me to joining the team at Presto Geosystems. My goal was to find a role that would allow me to use my existing skills, but would also be able to challenge me. My background in the manufacturing industry plus my prior experience with lead generation made the position at Presto very appealing to me.

There are many routes you can take with a degree in Marketing. One reason I gravitated towards a career in business development was the opportunity to work in all different aspects of the business, including sales, marketing and customer service. I enjoy the wide range of responsibilities when working in this role, as well as being able to build relationships with end-users, distributors and my fellow teammates.

Could you walk us through a typical day for you at Presto Geosystems?

Every day seems to entail something new here at Presto Geosystems, which keeps things interesting. For example, I never thought I’d be writing a blog post, but here I am!

One of my main responsibilities is managing leads and opportunities in our CRM system. Leads are generated when someone fills out one of our webforms, requests a complimentary project evaluation, attends a webinar and more. After I receive these leads, I then connect these customers with one of our distribution partners who will further assist with their project needs. It is also my job to respond to all general customer inquiries and technical questions, as well as assist with various administrative tasks.

What’s a skill you’d like to master?

I don’t know if this necessarily qualifies as a skill, but one thing I’d like to be better at is being more present and living in the moment. One of my New Years resolutions was to reduce screen time, which I have been successful at this year. However, if you are looking for an actual “skill”… I would have to say waterskiing. It is an inside joke between my family, as well as something my brothers enjoy making fun of me for. I attempt it every summer, but usually just end up ingesting way too much lake water.

What’s the most interesting thing you’ve learned so far during your time at the company?

The world of geosynthetics was completely foreign to me when I started at Presto a few months ago, so I feel like I am constantly learning something new every day. Overall, what I find to be the most interesting is the history of geocells. For those that do not know, in the 1970s, the U.S. Army Corps of Engineering needed a confinement system for load support, and thus, the geocell was born. It is very cool to see pictures of some of the first installations that took place decades ago, as well as see how the product has evolved since then. Aside from that, it is interesting to read about all the different projects from all over the world where GEOWEB® has successfully been utilized.

When you’re not working, what are some of your favorite hobbies or activities?

Nothing makes me happier than spending time with my loved ones. One major perk of residing in a small town is living within a two-mile radius of the majority of my friends and family. I love having my parents over for dinner, hosting game nights for my friends and being able to see my niece and nephew on a regular basis.

I consider myself to be quite crafty and enjoy DIY projects. I spend more time on Pinterest than I’d like to admit. In the past few years, I have started to enjoy reading. While I may be a few years late to the game, I recently started reading the entire Harry Potter series. In the summertime, my favorite place to be is the Lake of the Ozarks in Missouri. I have been going there my entire life and appreciate the quality relaxation time more and more the older I get.

Though it can be heartbreaking at times, my favorite sports teams to root for are the Chicago Cubs, Chicago Bears and Fighting Illini. I am well aware they are not always the best, but I am still loyal!

If you could meet anyone, past or present, who would it be?

Perhaps it’s just the times we are living in… or perhaps it is because I am a millennial… but I’m going to have to say Taylor Swift. While I may not know all her songs or be a die-hard “Swiftie” like some others, she truly just seems like the most captivating person in the world right now. Whether she is performing her sold-out international tour, attending NFL football games, or just grabbing a bite to eat, everything she does seems to be top news nowadays. Overall, she just seems like a normal girl, despite being mega famous, and I like to think we would be good friends if she got to know me. Oh—and during this meet-up, I would kindly ask if she could spare some tickets for the next round of the Eras tour for me and some friends.

What’s the most interesting place you’ve visited?

A few years ago, I visited Bryce Canyon National Park in Utah with one of my best friends. The bright orange hoodoos and rock formations are absolutely breathtaking and truly something out of this world. I love looking back at all the pictures I took from my day there because the scenery was just so incredible. If you haven’t been, I highly recommend adding it your bucket list.

I have never left the country, but am hoping to explore other continents and discover more interesting places within the next couple years.

What’s something you’re looking forward to either personally or professionally in the coming year?

Professionally – I am excited to continue learning about the world of geosynthetics and engineered soil stabilization solutions, as well as getting more familiar with all our products.

Personally – I am at the age where it seems like everyone in my life is getting married. I have weddings to attend in Utah, Florida, and Chicago all within the next year; however, I am most excited for my younger brother’s wedding in Cancun next May. I am looking forward to all the fun to come within the next year (though my bank account is not).

Addressing Microplastics: How GEOWEB® Geocells Contribute to Eco-friendly Soil Stabilization Practices

Posted September 19, 2023 by Ashley Beyer

geoweb channel with no microplastics symbol

Written by: José Pablo George, M.S., CPESC-IT, International Business Manager

Microplastics, tiny plastic particles smaller than five millimeters, present a potential hazard to both wildlife and marine organisms. As revealed by a global microplastics database provided by the National Centers for Environmental Information (NCEI) and published by the National Oceanic and Atmospheric Administration (NOAA), plastic is the dominant type of marine debris in the ocean and the Great Lakes. These microplastics, usually originating from single-use, disposable plastics on land, are transported via rivers and wind into global circulation systems where they accumulate.

International Measures and Guidelines: A Proactive Response to Plastic Pollution

The United Nations Environment Programme´s Intergovernmental Negotiating Committee and Environment Assembly have adopted an international legally binding instrument on plastic pollution to address plastic pollution throughout its life cycle. Given the array of different types of plastics, the Sea Studios Foundation, in conjunction with Earth911.org, the Institute of Agriculture and Trade Policy, the WHO International Programme on Chemical Safety, and the US EPA, has published a Smart Plastics Guide. This guide outlines seven commonly used plastic types and their potential health hazards.

There are some plastics (often used for disposable packaging) that are not easily recycled and may contain harmful chemicals posing health issues. Others, such as PET and HDPE, are easily recycled, pose no known health issues, and can be used beneficially in environmental applications. Given the potentially harmful effects of microplastics on human health and the environment, it’s crucial to consider the types of plastics we use and their complete life cycle.

Geocells: An Environmentally Safe Solution for Soil Stabilization

For over four decades, the GEOWEB® Geocells, which are manufactured from premium high-density polyethylene (HDPE) resin, have been used for soil stabilization. They interact directly with soil and water systems without posing significant environmental risks. This HDPE material, free of fillers, polymer alloys, and compatibilizers, is akin to those used in environmental applications like geomembranes to prevent the spread of harmful toxins.

Third-party geosynthetic laboratories have confirmed the GEOWEB Geocells’ long-term stability against environmental factors, including weathering and oxidation. According to EN ISO 13438 analysis, they are expected to last at least 100 years in natural soil. Furthermore, even under UV radiation and accelerated weathering conditions per EN 12224, GEOWEB specimens maintain their original tensile strength, appearance, and mass.

The Danger of Microplastics in Polymer Blends

This isn’t true for all geocells, however. Some manufacturers advocate for the use of polymeric alloys containing nylon and polyester particles “dispersed in a polyethylene matrix.” Essentially, this means blending materials typically incompatible with HDPE, requiring the use of specialized chemicals, or compatibilizers, to ensure compatibility. Research indicates that such polymer blends may be a significant source of microplastics in the environment, particularly as alloys age more rapidly due to weathering. This aging process can lead to the production of microplastics as the blended components break down.

Geosynthetic Soil Stabilization: A Response to Climate Change

Well-designed geosynthetic soil stabilization systems, using high-quality, HDPE-only geocells (a “good” plastic), can help mitigate the long-term impacts of climate change. With its durability parameters, structural integrity, and system performance, the GEOWEB Geocells are an environmentally safe choice for soil stabilization and water needs. Crafted from sturdy high-density polyethylene (HDPE) since its inception, GEOWEB geocells provide the highest, longest-lasting, and most proven performance in civil applications.

workers installing geocells on streambank

Presto Geosystems guarantees quality and offers more than 40 years of expertise. We ensure each shipment meets or exceeds our specifications, so you can build with materials you trust. No hidden terms or concerning fine print. Just strength, from the ground up, since 1979.

See Sustainable Environmental Contributions for the GEOWEB® System.

Ballast Stabilization Using Geocells

Posted July 27, 2023 by Katie Bocskor

The Often Overlooked Importance of Junction Efficiency as a Key Design Consideration

A significant number of research studies have been carried out to investigate the benefits of using geocells in railway track bed applications. Combined with an ever-expanding list of successful projects from around the world, the benefits of using geocells in rail ballast stabilization is well-documented. Rail operators understand that durable track geometry starts with a solid foundation, and geocells have emerged as a powerful value engineering tool for reinforcing ballast and sub-ballast layers while optimizing layer thicknesses.

Many practitioners may not be aware of the critical role that geocell junctions (both mechanical and internal) play in ensuring that the installed system performs in a uniform and consistent manner. In track bed stabilization applications, non-uniform junction performance can lead to differential settlement and localized subsidence—which in turn can lead to serviceability issues, damage to the overlying structure/pavement, and a reduction in overall design life. In essence, poor junction performance can nullify all the intended benefits of a geocell system.

This article will succinctly discuss the different types of junctions present in geocell systems, failure mechanisms and test methods, and the concept of junction efficiency as a performance parameter.

Types of Geocell Junctions

There are two types of junctions present in any geocell system: internal junctions, the factory-welded seams that create the interior cells of the panel, located within the body of a geocell panel; mechanical junctions located around the perimeter of an individual panel, formed during installation when adjacent panels are connected in the field, creating mechanically joined cells along panel joints. Since a primary mechanism by which geocells provide benefit is through lateral confinement of the infill, it is vital that both types of junctions remain intact during construction and throughout the design life of a project.

Junction Performance: Failure Mechanisms, Current Test Methods

Dating back to original research performed by the U.S. Army Corps of Engineers in early geocell development, much of the focus on junction performance was limited to peel strength of these internal junctions, with less consideration for mechanical junctions or other potential modes of junction failure. International Standard ISO 13426-1, “Strength of Internal Structural Junctions – Part 1: Geocells” presents standard test methods for evaluating several possible failure mechanisms for geocell junctions, including failure in shear, peeling, and cell splitting. What is lacking in ISO 13426-1 and similar standard test methods is a way to relate these failure mechanisms to the tensile characteristics of the cell wall itself.

Geocells are comprised of single strips of high-density polyethylene (HDPE) joined together. From a structural integrity perspective, these junctions should be expected to perform at a level that is equal to or better than that of the cell wall itself to ensure uniform and consistent performance. This is where the concept of junction efficiency comes in.

What is Junction Efficiency?

Junction Efficiency is a ratio (typically presented as a percentage) accounting for all three primary modes of potential junction failure (shear, peeling, splitting), and compares measured junction strength values to the tensile properties of the perforated cell wall. Separate values must be determined for internal and mechanical junctions.

In the case of mechanical junctions, the type of connection must be specified, with laboratory samples consistent with in-field installations. If the mechanical junctions will use staples, then representative laboratory tests must incorporate all relevant aspects of the stapling method, including material (stainless steel vs. aluminum), gauge, minimum number per junction, and vertical/horizontal spacing necessary to achieve junction performance requirements. Similarly, if cable ties or two-piece connectors are the recommended connection device, then their break strength, material composition, durability, length, and assembly instructions must be specified and tested.

In the case of GEOWEB® geocells, mechanical junctions utilize Presto Geosystems’ patented ATRA® Key. ATRA Keys are simple to use and provide consistent, reliable mechanical junction performance for the life of the project. As shown in the table below, GEOWEB geocells facilitate junction efficiencies in excess of 100% for both internal and mechanical junctions, offering robust protection against the primary modes of junction failure.

Introducing Presto Geo P³: Expanding the Universe of Value Engineering Solutions Available to the AEC Industry

Posted July 20, 2023 by Ashley Beyer

Project planning and design is a complex task, often demanding a strategic blend of professional judgement, cost considerations, risk, and sustainability. In response to these challenges, Presto Geosystems developed the Presto Geo P³Project Planning Portal, a free, web-based suite of geotechnical calculation tools. Designed with engineers, contractors, landscape architects, and project owners in mind, Presto Geo P³ streamlines your project planning process, allowing you to quickly perform calculations to evaluate a wide range of possible technical solutions for your project.

Presto Geo P<sup>3</sup> Unique Features & Benefits

With its pioneering support for geocells—a first in the industry—and integration of calculations for aggregate and vegetated porous pavements and site access, the Presto Geo P³ portal sets a new standard in value engineering evaluations.

Key offerings of the Presto Geo P<sup>3</sup> include:

Geotechnical Calculations:
- Soil Stabilization: Unpaved, Flexible Pavements, and Rigid Pavements
- Porous Pavements: Vegetated and Aggregate Surfaces (Rigid and Flexible)
- Site Access: Access Roads
Personalized Dashboard: Users can efficiently organize their projects and associated calculations for easy access and review.
Customizable Output: Detailed calculation output with customizable fields for your project/firm/client name, a summary of input parameters and calculation results, and a cross-sectional graphics illustrating user-selected layer thicknesses and material types.

Resource Library

Presto Geo P³ also serves as a comprehensive resource hub. With access to a vast library of technical documents and product resources, you can deepen your industry knowledge, stay up-to-date with the latest product advancements, and make more informed decisions when it comes to your projects.

Designed to revolutionize project planning and execution, Presto Geo P³ empowers you to build smarter, faster, and more sustainably. Start planning your next project today.

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

Posted June 9, 2023 by Ashley Beyer

truck driving over sand filled geoweb road

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.

Tip #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” >>

Conserving Natural Resources Using Geosynthetics

Posted March 1, 2023 by Katie Bocskor

Written By: Cory Schneider, Environmental Scientist, Presto Geosystems

Natural resources are finite, or at a minimum, can easily be consumed faster than they can be replaced. As such, the conservation of natural resources is a pragmatic endeavor. Geosynthetics—widely available materials used in construction, civil engineering, and environmental protection—can be useful in promoting the conservation of these resources. When used as intended, geosynthetics can enhance soil properties and reduce the demands placed on natural resources.

Types of Geosynthetics

Geosynthetics are typically made from synthetic polymers, such as polyethylene, polypropylene, and/or polyester, and are designed to be durable and resistant to weathering and other environmental factors.

General groupings of geosynthetics include:

geotextiles,
geogrids,
geomembranes,
geocells,
erosion control blankets (ECBs),
and turf reinforcement mats (TRMs).

Geotextiles (permeable) and geomembranes (impermeable) provide separation, while geogrids and geocells provide varying degrees of stabilization and confinement. ECBs and TRMs, made with a combination of natural and synthetic fibers, resist surficial erosion by preventing seed washout prior to germination.

Application areas where these geosynthetic materials are used typically include:

load support,
slope, shoreline, and channel protection,
and earth retention.

Using Geosynthetics in Load Support Applications to Conserve Natural Resources

In load support applications, geogrids, geotextiles, and geocells can all be used to reduce structural cross-section depths, thereby conserving natural resources. The figure below illustrates this benefit and provides a comparison of four structurally equivalent unpaved road sections over a very weak subgrade with a CBR of 0.5%.

As shown, the conventional cross-section in this case would require more than 36 inches of aggregate to achieve minimal stability, while the planar geosynthetic option (geogrid + geotextile) would require 26 inches of aggregate. Most notably in this case is that geocells—specifically the GEOWEB® Geocells—can be used to achieve an optimal section thickness of only 15 inches, and where suitable on-site material (OSM) is available, it is possible to limit imported aggregate to just the wearing course.

How Geocells Conserve Natural Resources

Through full-depth confinement, geocells allow for the use of lower-quality, non-cohesive soils and recycled materials (concrete, asphalt), further conserving resources through beneficial reuse. Beneficial reuse of any of the aforementioned reduces imported material requirements, thereby conserving aggregate, and with the additional benefit of less truck traffic to the site, conserves oil and gas and puts less stress on local roadways. Properly designed geosynthetics can also increase your roadway´s useful life and reduce or eliminate maintenance needs.

In slope, shoreline, and channel applications, ECBs, TRMs—and to a further extent—geocells, help prevent surficial soil erosion—a process that can cause significant damage to natural ecosystems and lead to the loss of valuable topsoil. While ECBs and TRMs are suitable to protect the surface, adding geocells to the cross-section can prevent supersaturated soils below these products from washing downslope or downstream, and can improve the hydraulic performance of the materials used in the geocells.

Finally, geosynthetics can be used in constructing retaining walls and embankments, which can help conserve resources by reducing the need for land excavation and fill. In retaining wall construction, geogrids—and occasionally geotextiles—are used as tiebacks in Mechanically Stabilized Earth (MSE) structures, while geocells and TRM wraps are just a few of the many different geosynthetic facing options available. Geocells can not only be used to create living green walls to help stormwater infiltrate naturally and add an aesthetically pleasing finish to a structurally sound engineering solution, but research has also shown that geocells can withstand high levels of seismic shaking and may be a suitable option in many earthquake-prone parts of the world.

Let Our Engineers Run Design Calculations on Your Next Geocell Project.

See the Cost and Material Savings for Yourself!

Presto Geosystems’ engineering team works closely with you to provide free project evaluations, with engineering support from the preliminary stages through construction. The project evaluation will deliver a technically sound, cost-effective solution based on four decades of accredited research and project experience.

Contact our knowledgeable staff and network of qualified distributors to discuss your project needs today and see how we can help you save money while conserving natural resources. Responsible use of engineered materials designed for long-term performance in the environment can help you achieve a more sustainable approach to construction.

Use our free online tools to keep your projects moving forward.

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