Geosynthetic Material and Its Functions
Geosynthetic material is a permeable textile material used with foundation, soil, rock or earth as an integral part of civil engineering projects, structures and systems. Geotextiles are generally classified as woven or nonwoven and perform at least one of the conventional functions of separation, filtration, drainage and reinforcement.
Woven and nonwoven geotextiles can be further subdivided into a variety of forms as shown in Fig. 7.2. Geogrids represent a growing segment within the geosynthetics industry.
Reinforcement
A geosynthetic material is a man-made textile made to enhance the performance of civil engineering structures by separation, filtration, drainage, reinforcement and soil stabilization. The material can be a solid or perforated sheet, a pipe, a range of textile structures such as woven and non-woven, or a combination of these to form a geocomposite.
A comprehensive design methodology for geosynthetic materials must consider the effects of both their index and performance properties. This is particularly important when considering the application of geosynthetics in unusual circumstances, such as clogging by fine cohesionless silts, highly turbid liquids and microorganism laden soils.
When using a Geosynthetic as a reinforcement in the construction of slopes, it is often necessary to consider vertical stress. The calculation of vertical stresses must Geosynthetic material geotextile account for the force generated at the geosynthetic interface with the slope and the shear strength of the Geosynthetic itself.
It is also possible to elect to consider the additional failure mode of a slip surface sliding along the Geosynthetic interface, (via the Pullout and Stripping tab > Consider sliding along interface). When this option is toggled, the computations will also consider the Geosynthetic as a weak layer which clips the slip surfaces that intersect it.
Filtration
Filtration in geosynthetic material is an important function as it protects the underlying soil from being degraded or contaminated by external forces. In this way, it reduces the cost of maintenance of the underlying ground structure. This is achieved by allowing liquid flow across the plane of the geotextile whilst retaining soil particles. Geotextiles can also be designed to have specific filtering properties based on the intended soil conditions.
The permeability of a geotextile is designed to be much higher than that of the surrounding soil. This allows the water to move through the geotextile at a rate that is more than 1,000 times faster than that of a typical soil. This feature is especially important when used as a geocell in hydraulic embankments, or for critical applications such as below riprap protection of river and coastal works.
Geosynthetic materials are often combined with other geotechnical products to form geocomposites. This is done to increase the functionality of the product, and to better suit project requirements. Examples of this include composite geotextiles which provide two or more conventional functions in one material, and smart geosynthetics which can provide critical management information.
Whether used for erosion control, separation, reinforcement, drainage or filtration, polymeric geosynthetics are an integral part of many civil engineering projects. This is because they offer high performance, durable solutions for difficult ground conditions and challenging environmental projects. This paper explores four select case studies of transportation infrastructure projects that have used geosynthetics to enhance the performance of infrastructure. Each case study details the type of geosynthetics used, design methods employed and performance results.
Drainage
A geotextile acts as a drainage system by carrying fluid flows through less permeable soils. It also dissipates pore water pressure in roadway embankments, protects against localized shear failure in soft soils, and allows construction over wet soils. It can also prevent clogging of drainage pipes and increase the capacity of the existing drainage system.
Geosynthetic materials are one of the most revolutionary product groups within civil engineering, allowing infrastructure works to be constructed more economically, sustainably and with greater resilience. The Tensar guide offers a comprehensive introduction to the range of geosynthetic products, describes how they are manufactured and presents four infrastructure case studies demonstrating how the use of multifunctional geosynthetics can significantly enhance the performance of transportation and civil engineering projects.
There are two major groups of geotextiles: woven and non-woven. Woven geotextiles are planar textiles produced by interlacing sets of strands at right angles to each other. They are available in two forms: slit film and monofilaments, which can be either flat or round. They are porous to liquid flow across their manufactured plane and within their thickness, but to a different extent for each type of fabric. They are used in separation, reinforcement, filtration and drainage applications. Non-woven geotextiles are matted together in a random non woven manner or knitted and are also porous to varying degrees, depending on the type of fabric.
Separation
When placed between dissimilar materials like paved or unpaved roads, railroad bases and soils, geotextiles provide a barrier to ensure that both materials’ integrity and function remain intact or improved. This is the primary separation function of geotextiles.
Geotextiles used for stabilization and filtration often incorporate drainage functions, allowing water to pass through the fabric into a drain or other open space. This function is especially important for roadways as the presence of excess water under a road’s surface can lead to softening of the basement layer, reducing the strength of the entire structure. Drainage geotextiles are typically found under retaining walls and behind embankments, among other places.
Geosynthetic materials are manufactured in a controlled factory environment, allowing for quality control and consistency in properties and design. Most are characterized by a variety of material properties that are dependent on their function, with reinforcement and filtration functions depending primarily on mechanical properties, and drainage and permeability functioning depending largely on hydraulic properties. These dependencies impose certain restrictions on how geosynthetics are tested, resulting in the need for geotextile membrane manufacturers test methods to be developed, standardized and refined. This requires collaboration between researchers and engineers to achieve long-term performance in various conditions of use.
