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… Read more »
Posts Categorized: Geocell Confinement System
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. 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 Ultrabasic soils cover about one-third… Read more »
The Dangers of Breaking Specs and Bid Shopping
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… Read more »
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. 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. 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… Read more »
Addressing Microplastics: How GEOWEB® Geocells Contribute to Eco-friendly Soil Stabilization Practices
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… Read more »
“Or Equal” Substitutions in Geosynthetics: Evaluating the Contractor’s Proposed Alternative Amidst Global Supply Chain Disruptions & Rising Costs
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… Read more »
7 Key Factors to Choosing the Right Geocell
Choosing the Right Geocell Does excellent quality and support matter to you? Of course it does. But, you are smart enough to know that there is no free lunch. Low cost alternatives are less expensive for a reason. So, what do you need to look for to recognize the right geocell for your project? Quality Feedstock Insist upon verifiable proof that your geocell is manufactured only with virgin high density polyethylene. While it is possible to achieve poor weld strength with virgin materials, it is impossible to achieve consistently excellent weld strength unless only virgin high density polyethylene is used. Integral Components Choose a geocell that offers connection components, tendons, stakes, load transfer clips and installation tools that are specifically tailored for the system. Using rope, staples, bent rebars (J hooks) and zip ties that are not specifically designed for use with a geocell engineered solution is unwise and potentially catastrophic. Use only designs that recognize the critical nature of these components to the overall success of the project. Experience and Warranty Choose a manufacturer who has thousands of projects and decades of experience. It is shocking how little some manufacturers understand about the principles and practices of engineering and… Read more »
Protecting Environmental Geomembrane Covers With Suspended GEOWEB Geocells
Economic pressure, the desire for green solutions, and the intensification of climate extremes have converged to create a need for better methods to effect soil stabilization. Fortunately, a proven technology exists that addresses issues associated with these conditions and provides a more stable cover solution for landfill covers, lagoons, stormwater containment basins, and other geomembrane-covered systems. Soil, aggregate, and concrete protective covers over geomembranes can be secured against known gravitational, hydrodynamic, and seismic forces using the GEOWEB® Soil Confinement System. Soil and aggregate are commonly used as a protective cover over liners on slopes of 3H:1V or less. However, when slope gradients are greater, unconfined soil and aggregate covers are typically unstable and not used. In arid areas, cover depth may range from 75 mm (3 in) to 150 mm (6 in). Where conditions support vegetation, cover depth may range from 100 (4) to 600 mm (24 in) or greater where the final depth is a function of the characteristics of the desired vegetation. Regardless of cover depth, if an extreme rainfall event occurs that is 10%, or greater than what would typically be expected, soil mass increases, assumed friction angles decrease, and factors of safety for soil stability drop to… Read more »
GEOWEB Geocells Combined with a Turf Reinforcement Mat (TRM)
GEOWEB® System – Research Synopsis Research Objective Measure the performance of the GEOWEB (GW) material combined with a turf reinforcement mat (TRM) (integrated system) with topsoil infill and vegetation under varying shear stresses and flow rates to quantify both hydraulic forces and corresponding soil loss. The test consisted of a series of continuous one-hour flows over the GW-TRM system at incrementally increasing discharges. The performance threshold was defined as the point at which 0.5 inches (13 mm) of soil loss occurred. Research Scenario The Research Facility Steep-Gradient Overtopping Facility (SGOF) at the Hydraulics Laboratory of the Engineering Research Center (ERCD) at Colorado State University (CSU), Ft. Collins, Colorado Test Timeframe April 2005-August 2006 Test Materials GEOWEB Soil Stabilization System North American Green C350 Turf Reinforcement Mat Scope of Test Hydraulic performance testing was conducted on an integrated system comprising the GW30V textured/perforated GEOWEB System and the North American Green C350 composite turf reinforcement mat. The C350 TRM was chosen for its known performance in the test apparatus. Six tests were conducted under the research program to measure the performance of the integrated system, identify stability threshold conditions, and quantify both hydraulic forces and soil loss. Assembling the Test Components The… Read more »
Solar Installations on Closed Landfills: Using Geosynthetics to Overcome Redevelopment Challenges
Written by: Michael Dickey, P.E. (WI, FL, GA, NC), Director Redevelopment of closed landfills and capped solid waste sites represent a unique opportunity for landfill owners, solar developers, and communities to work together to put underutilized properties back into productive use. Moreover, many such sites are conveniently located near existing transmission infrastructure and may be easier and more economical from an interconnection standpoint than rural greenfield sites. However, building over a closed landfill poses unique challenges because most landfills are covered by an engineered cap not typically designed to support loads from permanent foundations or heavy equipment. Additionally, state and federal regulations generally prohibit any activity that could potentially breach or damage the cap. Therefore, retrofitting a closed landfill for utility-scale or community solar projects requires careful planning. Ultimately, the project must not jeopardize the intent of the original cap design; that is, to protect human health and the environment. Selecting a Suitable Foundation Concrete slabs and pre-cast ballast footings are both foundation options for solar system installations on landfill caps. In general, concrete slab foundations are heavier than ballast footings and pose a higher risk of creating landfill settlement and side-slope stability issues. Ballasted footings are a lighter-weight option… Read more »
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