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… Read more »
Posts Tagged: Geocell
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 »
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 »
Railroad ballast performance improvement using GEOWEB® Geocells
Each year railroads must allocate a significant portion of their capital and maintenance budget toward the creation and upkeep of high-quality ballast layers. Enduring, well-designed ballast is quite literally the foundation on which a successful rail line operates. With ballooning rail traffic carrying heavier loads than ever, GEOWEB cellular confinement (geocell) effectively takes the pressure off critical ballast systems. Oregon State University (OSU) recently performed state-of-the-art, three-dimensional dynamic Finite Element modeling to analyze the reinforcing benefit of GEOWEB geocells in railway applications. Completed in cooperation with the University of Kansas (KU), who simultaneously performed a testing program of Geocell-reinforced ballast placed over weak subgrade. The digital modeling results were reinforced by the laboratory tests and showed a significant decrease in settlement of the railway ballast when GEOWEB confinement was used. Using the GEOWEB system not only decreased settlement but also reduced pressure on point-to-point aggregate load transfer contact. This resulted in less damage to ballast aggregate particles leading to less progressive deformation and longer maintenance frequencies of the entire ballast embankment. In short, more cycles mean less track down-time for maintenance. The research results were clear. The benefits of applying GEOWEB Geocell confinement for reinforcement of real ballast over weak… Read more »
Choosing the Right Geocell
Written By: Bryan Wedin P.E., Chief Design Engineer, Presto Geosystems Not all geocells are created equal. While most manufacturers can provide similar-looking written specifications, you need assurances that the material delivered for your project is of the high quality that you expect. Important factors in the success of your geocell project include: Quality The geocell material is proven, strong, and will last Require only the highest quality virgin High Density Polyethylene (HDPE) resin Low quality or recycled resin can lead to weak and/or inconsistent seam strength, putting the success of your project at risk. Non-HDPE materials cannot match the nearly 40 years of in-ground experience of HDPE geocells and plastic alloy proprietary blends can mask cheap stiff filler materials. ISO Certification Important, but the manufacturer sets the testing protocol for the certification. Require a Certificate of Analysis (COA) for the material that is shipped to your project. An ISO certification that does not require continuous testing is lacking. Integral Components The complete solution includes proper components Non-corrosive, high-strength panel connection method (ATRA® Keys vs. weak staples or zip ties) Anchors that provide secure connections to the geocell (ATRA® stakes vs. J-hooks) Load Transfer Devices for tendon applications that are non-corrosive and… Read more »
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