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Green Retaining Walls Protect an Advanced Wastewater Treatment Plant from a 500-Year Flood Event

GEOWEB Green Retaining Wall

Flood Protection Plan

To meet federal requirements for flood mapping of levee-protected areas, a levee reconstruction project for the Indianapolis Southport Advanced Wastewater Treatment (AWT) plant along Little Buck Creek was part of a more extensive Deep Rock Tunnel Connector project—one of the largest combined sewer overflow projects for the City of Indianapolis.

The project included plans to protect the Southport ATW plant and wastewater-processing pond from a 500-year flood event from an adjacent creek and river. To accomplish this, a wall system designed on the creek side of the levee would have to maintain a narrow profile to increase the water capacity of the creek.

A Natural Erosion Protection Solution

Flood events and high water flow from the adjacent creek caused significant toe erosion of the levee embankment along the north side of the wastewater treatment plant. The AWT required a long-term soil stabilization solution to combat erosive forces from Little Buck Creek’s varying depths and flows. The creek flows as low as a 1-foot depth with velocities of 3 feet per second (fps) to as high as 8 fps with a depth of 12 to 15 feet during a flooding event.

The project engineer preferred a wall system with native vegetation along the levee that would be robust enough to withstand erosive forces from the creek. They chose the GEOWEB® Vegetated Retaining Wall System to reduce the environmental impact, protect the levee from scour and erosion, and satisfy regulatory requirements.

Construction of the Levee Wall

levee wall being constructed with geocells

Working within a limited footprint to maintain a narrow profile, the engineer designed the GEOWEB Retaining Wall as a gravity structure. Installers filled the back cells of the GEOWEB System with aggregate to promote drainage and placed a mixture of topsoil and #2 stone in the front outer cells to support vegetation and provide stability and resistance to soil loss during larger storm events.

Wall Dimensions & GEOWEB Green Wall Attributes

  • Wall length: 1,500 feet; Wall height: 5 to 12 feet
  • Open fascia cells allow infiltration of stormwater.
  • Green fascia panels blend with natural environment.
  • Flexible wall performs well in soft soil environments; conforms well to a waterway’s geometry.
  • The GEOWEB HDPE material is unaffected by water contact.

Performance Update

Since its installation in 2012, the GEOWEB green wall continues to provide vital protection to the Southport ATW plant and wastewater-processing pond from major storm events. Significantly more economical than the U.S. Army Corps of Engineers’ (USACE) conventional riprap solution, the GEOWEB walls are a practical alternative for levee applications.

With native vegetation, the GEOWEB levee wall proved to be an attractive solution that effectively minimized environmental and permitting impacts.

Living Green Walls + Low Impact Development

An attractive alternative to MSE block walls or riprap, walls built with the GEOWEB geocells offer a green aesthetic and low-environmental impact approach to designing retaining walls. The GEOWEB Retaining Walls conform well to landscape contours, are resistant to environmental degradation, and install 25-30% faster than MSE block walls. The GEOWEB System also offers design flexibility for a variety of wall configurations, including gravity, reinforced, and steeped slopes.

Create Strong, Long-Lasting Mechanical Connections Using the New ATRA® Wall Key The new ATRA Wall Key is the most effective device for connecting 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 Key provides 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.

The innovative ATRA Wall Key includes an integrated washer at the base of the handle to provide coverage of the I-slots, frictional barbs for an improved interlock with the GEOWEB sections, and an ergonomic handle with S-shaped contouring for ease of installation.

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 ATRA Wall Keys is faster than using staples or zip ties, requires no tools, and can be completed by one installer with one easy turn.

Design Support for Retaining Walls

Presto Geosystems offers fast and easy-to-use resources and tools for designing GEOWEB Retaining Walls. Let our Design Engineering Team prepare a complimentary project evaluation for your next project. We also offer free licenses for our GEOWEB® MSE Design software for retaining wall applications.

 

Creep is not a factor for geocell load support

Written by: Bryan Wedin, Chief Engineer

An accurate understanding of creep resistance is essential to proper material selection when using polymers, and in the case of geocells, this science is being misapplied.

The definition of creep deformation is “the tendency of a solid material to move slowly or deform permanently under the influence of mechanical stress.”

This potential failure mode creates fear and uncertainty among designers wherever the possibility of creep factors exists. Yes, creep can occur in almost all materials including plastics, metals, and concrete. In cases such as bridge and building design, it is important to properly understand creep factors and account for creep in engineering calculations. However, in the case of designing with geocells for load support, creep factors have no relevance.

What causes creep?

In order for creep to occur, two factors must be present:

1) A constant load applied to the area and

2) A sustained deformation of the geocells.

Creep only applies when there is a sustained load on a material for an extended period. In a case of repeated on- and off-loading, this type of deformation would be governed by fatigue, not by creep, because it is not a constant applied load.

The second required factor for creep to occur is an ability to undergo sustained deformation of the material. When a polymer has a load applied, the molecules of the material start to pull apart and stretch. This leads to elongation of the material in one direction and typically results in a thinning of the material’s thickness.

Creep not a factor in load support

Now, consider a geocell load support application. The geocell material is expanded to cover the project area on-site and then an infill material is placed into the cells. At this point, there is not an applied load or deformation occurring in the material.

Next, the infill material is compacted. This compaction applies a load to the cells, but this load is removed as soon as the compaction equipment is no longer positioned over the cells.

As an individual cell is loaded, it exerts an outward force while each of the adjacent cells pushes back on it (passive resistance) and prevents any sustained deformation. Therefore, at the time of compaction, there is neither a constant load nor is there a sustained deformation. Thus far, the material is successfully installed without any creep effects.

 

After the geocell load support system has been installed, the two types of loads that will affect the system are driving (live) and stationary (parked) loads. When a vehicle drives over a geocell system, the load is applied vertically. As the geocell distributes the load laterally, there is a temporary load applied to the geocell material. The load is not a sustained load, and therefore, would not have a creep effect.

In the case of stationary loads, the load is continually applied to the geocell, so it meets the first criteria for creep. Due to the pressure from all adjacent cells surrounding the loaded cell(s), there is no ability for the cells to move enough to have any appreciable sustained deformation. Therefore, creep cannot affect this scenario.

ASTM D6992 creep test is not applicable

Those who make claims about creep potential in geocell load support applications have cited ASTM standard methodology as the reasoning for concern.

ASTM standards provide an accepted means for standardizing testing to be able to directly compare products. It is important to review the intention and scope of a test to ensure that it is appropriate and will give relevant results. The Stepped Isothermal Method (SIM) is used to accelerate creep testing. ASTM D6992 uses SIM to predict the expected deformation of geosynthetics over time when used for reinforcement applications. This method can be effective; however, it is not suitable for a polyethylene geocell evaluation.

ASTM D6992 5.3 Note 1 states, “Currently, SIM testing has focused mainly on woven and knitted geogrids and woven geotextiles made from polyester, aramid, polyaramid, poly-vinyl alcohol (PVA), and polypropylene yarn and narrow strips.”

Additionally, the note continues with a warning against expanded scope of the test saying, “Additional correlation studies on other materials are needed.” While this test has applicability for geogrids and geotextiles, the test is not intended for evaluating geocells and correlations for polyethylene have not yet been established.

Further, D6992 cannot be considered in isolation.

D6992 states, “Results of this method are to be used to augment results of Test Method D5262 and may not be used as the sole basis for determination of long-term creep and creep-rupture behavior of geosynthetic material.”

This reinforces the importance of reviewing each test standard to ensure that the product is within the scope of the test and that the results are relevant and complete. In the case of geocell evaluation, using ASTM D6992 is inappropriate as it has not been properly correlated to provide accurate evaluation of polyethylene and without ASTM D5262, it provides an incomplete overall evaluation of the product.

HDPE’s long history of success and repeatability

High Density Polyethylene (HDPE) has been used as the industry standard material for geocells since it was invented over 40 years ago. HDPE has been extensively researched by independent scientists across multiple industries, allowing for a comprehensive understanding of its performance capabilities. Using a virgin HDPE material allows for direct verification of resin consistency through laboratory testing to ensure that each manufacturing location and production lot have consistent material performance. This laboratory verification also allows for the comparison of the material to independent scientific results and does not rely solely on manufacturer’s claims.

Challenges with Fabricated Inelastic Blend (FIB)

A few geocell manufacturers are promoting a Fabricated Inelastic Blend (FIB) to cut manufacturing costs and increase material stiffness utilizing recycled and other unpublished polymer materials. These FIB-based materials can vary widely, even for the same product. Due to the vast number of combinations possible with FIB materials, they pose two key problems when included as a material choice: validation and consistency.

Because of the unpublished nature of the blending mixture there is no way to validate this material in comparison with published testing. Any testing of FIB materials must start from the beginning without any experience to rely on for long-term performance.

The second concern with FIB materials is controlling consistency of the blend. Because each FIB blend is so variable, there is no way for a third-party tester to fully determine consistency of the blend between different manufacturing plants or even between different production lots. This inability to determine consistency creates uncertainty because there is no way to determine if there has been improper blending or changes to material blend.

Manufacturers using FIB materials promote the advantages of increased material stiffness. This stiffness is often a function of multiple generations of recycling. It is important to review the differences between elastic and inelastic materials and how they affect geocell performance. An elastic material is able to undergo a deformation (strain) and then spring back to its original state without permanent (plastic) deformation.

Conversely, an inelastic material does not undergo immediate deformation, but rather ends in catastrophic (complete) failure. Many of engineering’s worst failures have resulted from catastrophic failures of inelastic materials that were subjected to unexpected loads. This absolute nature of inelastic failure puts projects at great risk because it does not give indication prior to collapse. With elastic materials, as material limits are reached, the material will stretch and yield prior to complete material failure. This yield zone allows for changes to loadings prior to catastrophic failure.

The mobilization of soil strain and geocell strain occurs from not only deformation of infill, but deformation of subgrade materials. For reasonable ranges of geocell stiffness, subgrade deformations will cause the strain to occur in the geocell system. For a given strain stemming from subgrade deformation, a stiffer geocell will realize larger tensile stresses, both in its wall and especially at the seam, which will result in seam rupture and system failure.

The material stiffness is not the most critical point in geocell performance. It is a combination of stiffness, tensile strength, seam strength, and passive resistance of adjacent cells. Published data shows that strain in geocell cell walls is on the order of less than 0.5 to 1.0%. At such low strains, the effect of creep should be ignored for all practical purposes. Properties such as seam strength, strip flexibility, environmental stress cracking resistance, and passive resistance from adjacent cells play a much larger role than stiffness of the material. Also, at these strain rates, HDPE (including virgin mixes, most recycled and other polymer alloy geocell) stress-strain behaviors are similar.

In load support applications, loadings are transient and quite small due to the stress-distributing behavior of the pavement material and geocell mattress effect, which further compounds the irrelevance of creep in reinforcement applications. Thus, overall system strength is not related to any performance factors that are tied to creep. Therefore, the focus should be on how much strain is mobilized in geocells.

Some manufacturers have examined theoretical 2% to 5% strain rates, both of which are far above actual field conditions, and therefore, not applicable. Five percent strains in load support applications are not applicable since compacted granular materials fail at much lower strain rates. At 2% strain, granular materials would fail within a geocell, as well as outside of the confined system, due to significant rutting and deformation. The geocell material would not be the failure point, and a stiffer geocell would not affect the failure of granular materials at 2% strain.

Geocells used in load support applications prevent high strains from occurring due to the very nature of the geometry, its confining behavior, and passive resistance of adjacent cells. Evaluating geocell material strength beyond reasonable strain values is not relevant for subgrade reinforcement as it contradicts actual measured data and represents conditions outside of practical design and application. The basis of comparison should focus on stress-strain behavior at very low strains – less than 1.0%. This information is readily available from large-scale laboratory tests, field tests, and numerical modeling.

True HDPE Performance vs FIB Results

FIB materials bring a new uncertainty to the geocell market. These materials are of unverifiable composition so connecting material to performance is nearly impossible. Ultimately, these FIB materials beg your trust in their performance touting their unnecessary creep resistance. They hide the truth that creep resistance comes at a cost – inelastic material that can fail catastrophically at the seam. FIB material prioritizes a single material property of the geocell at the expense of a uniformly designed system with measurable material consistency and applied field testing.

After 40 years, HDPE continues to be the industry standard material for geocells. Presto Geosystems proudly pioneered the use of HDPE material in its GEOWEB® Geocell products due to proven performance and reliability of that material.

Over these four decades, GEOWEB Geocells have been used in load support projects worldwide without a single failure due to creep effects. Although this consistent performance is impressive, it is not surprising given that creep forces are irrelevant in these applications.

Advancing Rail Resilience: How Geosynthetics Help Achieve CRISI Objectives for Robust and Stable Infrastructure

train along track stabilized with geoweb geocells

Discover the Latest CRISI Rail Infrastructure Funding Opportunities: Apply Before the May 2024 Deadline

 

The U.S. Department of Transportation is bolstering rail infrastructure advancements through the Consolidated Rail Infrastructure and Safety Improvements (CRISI) program. With a recent allocation of $2.47 billion, the CRISI program is set to significantly impact rail safety, efficiency, sustainability, and reliability across the United States.

This funding initiative is designed to support a variety of projects that are pivotal to enhancing the nation’s passenger and freight rail systems. It represents a call to action for rail industry professionals, including engineers, planners, and project managers, to leverage this opportunity to advance their rail infrastructure projects.

The deadline for application submissions is 11:59 p.m. ET, May 28, 2024. Professionals in the rail sector are urged to prepare their proposals that align with CRISI’s mission to improve the rail infrastructure’s overall landscape.

For a comprehensive overview of the application process and to assess project eligibility, stakeholders are encouraged to review the Fiscal Years 2023-2024 Notice of Funding Opportunity (NOFO) available through the CRISI program. This funding presents a pivotal chance for those involved in rail infrastructure to gain the support and resources needed to propel their projects forward.

The GEOWEB® Soil Stabilization System (Geocells): A Proven Solution for Rail Infrastructure

Mainline Ballast Reinforcement

geoweb geocells installed for mainline ballast reinforcement

The GEOWEB Rail Ballast Stabilization System stands out as an innovative solution for addressing ballast stabilization challenges, creating a more resilient and stable layer underneath the track. The 3D geocellular system yields unparalleled performance and construction benefits, surpassing the capabilities of 2D methods like planar geogrids or Hot Mix Asphalt (HMA), especially in areas with soft subgrades.

The performance of the GEOWEB system is backed by extensive research and rigorous field testing at renowned institutions such as TTCI and Oregon State University. It has demonstrated its ability to reduce settlement and track displacement under the strain of heavy freight loads on soft subgrades, and has already been adopted for use in railway track beds by international authorities in other advanced nations, such as Network Rail in the United Kingdom, with their recent published guidance on “The Use of Geocells in the UK Railway Track Bed”. Additionally, SmartRock testing by the University of Kansas revealed significant reductions in ballast abrasion, movement, and rotation, as further evidence the life of the ballast can be extended when the right geosynthetic product is incorporated into the project design.

Bridge Approaches, Crossings, Diamonds: Ballast Reinforcement in High-Stress Areas

Areas like bridge approaches, diamonds, turn-outs, and crossings face immense stress and usually require a lot of upkeep. The GEOWEB Soil Confinement System helps lower the need for maintenance in these challenging spots. It strengthens the ballast layer, reduces movement and deflection, and cuts down on maintenance in these crucial transition zones.

GEOWEB Geocells: BABA-Approved

Last year, the White House provided guidance on the Build America, Buy America (BABA) initiative. BABA specifies certain products must be manufactured in the United States to qualify for federal funding under the IIJA.

Selecting the GEOWEB System for enhanced track stabilization allows projects to achieve improved resilience and longevity, ensuring compliance with the standards set by the CRISI program, the Infrastructure Investment and Jobs Act, and Build America, Buy America. Presto Geosystems is ISO 9001 certified, and the GEOWEB Soil Stabilization System is 100% U.S. made. (A copy of our Certificate of Registration can be provided upon request.)

Need Assistance with Your Rail Projects?

Presto Geosystems offers free project planning support for all GEOWEB Geocells applications in rail projects. Our experienced engineers are ready to assist with project evaluations to ensure your project’s success from start to finish. If you’re dealing with challenges related to soil stabilization or looking for innovative track stabilization solutions, please reach out to us.

Request Free Project Evaluation

White House Provides Clarification on Build America, Buy America (BABA)

truck on partially infilled geoweb geocellsThe White House released guidance on the Build America, Buy America (BABA) initiative, an important component within the $1.2 trillion Infrastructure Investment and Jobs Act (IIJA) from 2021. BABA stipulates that certain products must be manufactured in the U.S. to qualify for federal funding in infrastructure projects and emphasizes the use of domestically produced construction materials.

As the faucet opens for IIJA projects, make sure your project has certainty and you are building with quality materials you can trust, 100% made in the USA.

BABA Highlights:

  • Scope: The BABA guidelines apply to federally funded infrastructure projects, including those under the IIJA.
  • Material Categories: BABA focuses on three primary categories: iron and steel products, manufactured products, and construction materials. Notably, the list has been expanded to include engineered wood but excludes coatings, paint, and bricks based on feedback.
  • Made in America Criteria: To wear the “Made in America” badge, a product must be produced in the U.S., with at least 65% of the cost of its components sourced domestically. This will further increase to 75% in the calendar year 2029.
  • Included Materials: The guidance specifically lists plastic and polymer-based products, non-ferrous materials, glass, fiber-optic cable, engineered wood, drywall and lumber.

Implications for Infrastructure Development

For manufacturers involved in infrastructure projects, these guidelines carry weight. The inclusion of polymer-based products, in particular, sheds light on the growing importance of innovative geosynthetic solutions in federal projects.

With BABA’s focus on polymer-based products, the GEOWEB® Soil Stabilization System offers a reliable solution for project stakeholders looking to utilize proven, U.S.-made geosynthetic products that align with federal directives.

Ascertaining Whether a Manufacturer Meets BABA Requirements

As the industry begins navigating this new terrain, project stakeholders can conduct their own screening-level due diligence to confirm if a specific product is manufactured in the U.S.

For example, one approach would be to determine if the manufacturer holds an ISO 9001 Certification, and if so, request a copy of their Certificate of Registration. The Certificate of Registration will list the address of the manufacturer’s production facility, and it will also identify which specific products are manufactured at that location.

We are pleased to share that Presto Geosystems is ISO 9001 certified, and that the GEOWEB® Soil Stabilization System is 100% U.S. made! (A copy of our Certificate of Registration can be provided upon request.)

 

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Geocell Technology Proves Effective in Solving Soil Stabilization Challenges for Solar Farms on Underutilized Lands

photo of solar panels on solar farm with blue sky and clouds background

With the increasing demand for clean energy, there is a growing interest in repurposing underutilized lands for solar farm developments, particularly abandoned mines, capped landfills, brownfields, and other unused areas. These locations offer a unique opportunity to transform unused spaces into sources of renewable energy, and can be particularly enticing because they are often situated near established transmission infrastructure. This makes the interconnection process simpler and more cost-effective than connecting to remote greenfield sites. In addition to contributing to the shift toward sustainable energy sources, the development of solar farms on underutilized lands can create jobs, generate revenue, and bring new life to areas that have been neglected or forgotten.

However, poor soil conditions can pose significant challenges for solar farm developers. To ensure the long-term success of solar projects, factors such as erosion control, stormwater management, and site access must be carefully considered during the design and construction phases, especially when repurposing underutilized lands for solar farm developments where the site conditions may be less than ideal.

GEOWEB® Geocells: A Versatile Site Development Solution for Solar Projects

Geosynthetics, specifically geocells, can be highly effective in mitigating the challenges posed by poor soil conditions during the development of solar farms. By reinforcing the soil and providing a stable base for access roads and balance of system (BOS) components, geocells can help distribute loads evenly and prevent soil erosion. Geocells can also be used to improve stormwater management, drainage, and filtration, ensuring that the solar farm site remains stable and functional in wet conditions.

Proper planning and execution, including the use of geosynthetics, can contribute to the long-term success of solar projects, reducing maintenance costs over time and minimizing environmental impact. In this article, we will discuss two projects that utilized the GEOWEB geocells in the development of solar farms.

Building a Solar Farm Site Access Road Using GEOWEB Geocells

installing geotextile and geocells for solar site access road

Residents of Brandywine, Maryland, recognized the benefits of redeveloping a closed quarry site into a community solar farm. However, poor soil conditions made it extremely challenging for crews and machinery to access the site for construction and future maintenance.

The EPC contractor for the project contacted Presto Geosystems and local material supplier Colonial Construction Materials to devise a solution that would meet their needs. To support heavy equipment during the construction phase and to ensure the required bearing capacity for emergency vehicles in accordance with local and state regulations in the long term, they opted for the GEOWEB® Load Support System with a vegetated infill to construct a permeable access road leading to the solar farm.

With the on-site support of Colonial Construction Materials, crews deployed the GEOWEB geocells over a non-woven geotextile to construct a geosynthetic-reinforced foundation layer for the unpaved road. The geocells were then infilled with a mixture of on-site material, imported stone, and topsoil to build a vegetated roadway capable of supporting heavy vehicle loads.

The GEOWEB geocells afforded the EPC contractor and project owners the ability to beneficially reuse on-site material to reduce imported material volumes, thereby offering a significant savings to the overall project construction costs. Moreover, using a permeable access road instead of a paved road provided the added advantage of decreasing the overall impermeable surface area at the site, in turn reducing runoff and associated stormwater management requirements, and bringing even more savings in terms of both up-front and long-term operations and maintenenance costs.

GEOWEB Slope Protection System: Protecting Solar Developments Against Major Storm Events

The Spotsylvania Solar Farm, a massive 617 megawatt utility scale solar farm covering 6,350 acres, posed unique erosion protection challenges that required a permanent stabilization solution. A sloped area leading into one of the larger detention ponds on the site was experiencing severe erosion due to concentrated stormwater flows.

Following multiple unsuccessful attempts to stabilize the surface using conventional erosion and sediment control practices (including hydroseeding, sod/staples, turf reinforcement mats (TRMs), etc.), the contractor opted for the GEOWEB Slope Protection System, citing cost and performance as the major determining factors. The GEOWEB system cell walls allow water to flow throughout the system while holding the soil in place, preventing soil loss and gullies.

The GEOWEB system (mid-size cells, 6-inch depth) was successfully secured over the 2:1 slope utilizing TP-225 tendons (woven polyester, 5100 lb. break strength) anchored to a buried deadman pipe and fastened to the cell walls using the patented ATRA® Tendon Clips – which provide twice the pull-through strength of any other tendon-based load transfer device. The ATRA Tendon Clips lock into the GEOWEB cell wall for the most secure connection on the market, and together with the tendons, can be preassembled at the top of slope prior to expanding for fast and easy installation.

After installation, the slope was hydroseeded and covered with a straw-coconut erosion control blanket. The GEOWEB® 3D Slope Protection System provides a structurally stable environment for topsoil and sustainable vegetation through a structured network of interconnected cells. The 3D GEOWEB system confines and reinforces the vegetated upper soil layer, and over time, will facilitate root mat entanglement with cell wall perforations, even further increasing system resistance to erosive and sliding forces.

first photo shows geocells installed on slope leading down to pond. second photo shows the same area vegetated with grass

The 3D GEOWEB system at the Spotsylvania Solar farm has held up to multiple high-intensity rain events, including the remnants of Hurricane Ian, which impacted the region with heavy rain and storms in September of 2022. The system will continue to provide robust erosion protection against similar major storm events in the future, allowing the Spotsylvania Solar Farm to generate reliable power for the local community.

Design Support & Resources for the GEOWEB System Applications

The engineering team at Presto Geosystems works closely with engineers and project planners, offering free project planning tools and on-site support. Our recommendations will deliver a technically sound, cost-effective solution based on four decades of accredited research and testing data.

 

 

A Week of Celebration and Inspiration: Engineers Week 2024

engineers week image

“Welcome to the Future!”: Engineers Week 2024

From February 18 to 24, 2024, the engineering community will come together to celebrate Engineers Week. This year’s theme, “Welcome to the Future!”, is a nod to the incredible advancements that have been made and a look forward to the innovations yet to come. It’s a week to celebrate, reflect, and inspire the next generation of engineers.

The Roots and Relevance of Engineers Week

Initiated in 1951 by the National Society of Professional Engineers (NSPE), Engineers Week has grown into a global celebration. It acknowledges the vital role engineers play in progressing our society. The week aligns with the birthday of one of history’s great engineers, George Washington, who was also a surveyor. This connection underscores the deep roots and enduring impact of engineering in our world.

Why “Welcome to the Future!” Matters

This year’s theme emphasizes the forward-looking essence of engineering. It’s not just about honoring past achievements; it’s about shaping the future. Engineers are instrumental in developing innovative solutions to some of the world’s most complex challenges, from climate change to advancing technology in renewable energy and communications. This week is an opportunity to showcase how engineering keeps us moving forward, turning today’s dreams into tomorrow’s reality.

Inspiring the Next Generation

A core aspect of Engineers Week is inspiring young people to explore engineering. With activities like Introduce a Girl to Engineering Day and various educational outreach programs, Engineers Week aims to spark curiosity and passion in the minds of potential future engineers. By showcasing the diverse and impactful careers in engineering, the week helps to cultivate a more inclusive and innovative future for the profession.

Innovating for the Future: The Role of Tools in Engineering Progress

During Engineers Week 2024, with its forward-looking theme “Welcome to the Future!”, we’re reminded of the importance of innovative tools in shaping the engineering landscape. The Presto Geo P3 Project Planning Portal is one such tool, designed to support engineers in navigating the complexities of modern project planning. It reflects our commitment to facilitating collaboration and enhancing efficiency in geosynthetic engineering projects. As we celebrate this week, our gratitude goes out to the engineering community worldwide, whose dedication inspires us to develop resources like the Presto Geo P3 Portal. It’s through collective efforts and shared tools that we can look forward to a future where engineering continues to achieve new heights.

Using Geosynthetics to Stabilize Soils in a Harsh Environment

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.

Mine Site Erosion

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, Cr = 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, Cr, 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

Written by Sam Justice, P.E.

engineers looking at specs

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.

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Why Geocells Outperform Geogrids for Road Construction

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.

Blog: Geogrids Product      Blog: GEOWEB Geocells Unpaved Roads

How do geogrids work?

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

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

 

 

Geogrids are difficult to install in soft subgrades

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

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

How do geocells work?

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

Blog: GEOWEB Geocell Load Support Diagram

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

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

Geocells are ideal for installation over soft soils

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

Geocells Proven Performance

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

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

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

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.

geoweb geocells

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.