# Geosynthetic Reinforced Steep Slopes: Current Technology in the United States
## 2 Geosynthetic Materials  
Geosynthetics are planar products manufactured from a polymeric material used with soil, rock, earth, or other geotechnical-related material as an integral part of a civil engineering project, structure, or system [14]. They are identified by the type of polymer, type of fiber or yarn, type of geosynthetic, mass per unit area or thickness, and any additional clarification needed to describe the geosynthetic. Geotextiles are defined as any permeable textile used with foundation soil, rock, earth, or any other geotechnical engineering-related material as an integral part of a manmade project, structure, or system. Woven geotextiles are cloth-like fabrics that are formed by uniform and regular interweaving of threads or yarns in two directions. They have regular visible construction patterns and, where present, have distinct and measurable openings. Geogrids are open grid-like materials of integrally connected polymers and are stronger than most geotextiles. Their primary use is soil reinforcement, because they can withstand heavy tension loads without much deformation and have low strain compared to geotextiles. Even though different geosynthetics may be manufactured with the same base polymer, their tensile strengths can vary widely. The tensile properties of geosynthetics are affected by factors such as creep, installation damage, aging, temperature, and confining stress. Some may also be more susceptible to environmental damage, including exposure to chemicals, heat, and ultraviolet light [15; 16]. The effect of long-term stress should be determined from laboratory creep tests in accordance with ASTM D5262 and extrapolated to the desired design life or carried out to rupture when possible [10; 17]. In ascending order, the most creep susceptible polymers are polyester, polypropylene, and polyethylene. An increase in temperature significantly accelerates creep for polypropylene [18]. Confinement may also change the creep properties of nonwoven geotextiles; however, for woven geotextiles and geogrids, the effect of confinement on creep is negligible [19]. For soil slope applications, Alabama Department of Transportation (DOT) specifies that the geosynthetic reinforcement (either geogrid or geotextile) shall be constructed of polyester, polypropylene, or polyethylene, resistant to all naturally occurring alkaline and acidic soil conditions, and resistant to heat, ultraviolet light, and to attack by bacteria and fungi in the soil [20]. Reinforcement for soil slopes shall be any geosynthetic whose strength in the machine direction equals or exceeds the values provided in the specification. California DOT requires for the percentage of the open area for geogrids to range from 50 percent to 90 percent of the total projection of a section of the material, and geotextiles shall have an irregular or regular open area with the spacing of open areas being less than 1 cm in any direction [21]. West Virginia DOT also requires the geosynthetics to be capable of withstanding 150 hours of testing as per ASTM D4355 with no measurable reduction in the ultimate tensile strength or deterioration of the coating [22; 23]. Table 1 provides additional recommendations for geosynthetic material based on soil environment [10]. Table 2 displays various geosynthetic types, properties, and test methods [1]. \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Soil Environment** & **PET** & **PE** & **PP** \\ \hline Acid Sulphate Soils & NE & ETR & ETR \\ \hline Organic Soils & NE & NE & NE \\ \hline Saline Soils (pH \(<\) 9) & NE & NE & NE \\ \hline Ferruiginous Soils & NE & ETR & ETR \\ \hline Calcereous Soils & ETR & NE & NE \\ \hline Modified Soils (Lime, Cement, etc.) & ETR & NE & NE \\ \hline Sodic Soils (pH \(>\) 9) & ETR & NE & NE \\ \hline Soils with Transition Metals & NE & ETR & ETR \\ \hline PP = Polypropylene, PET = Polyester, PE = Polyethylene & & \\ NE = No Effect, ETR = Exposure Tests Required & & \\ \hline \hline \end{tabular}
\end{table}