The application of geosynthetics in civil engineering is becoming more and more recognized nowadays because of its special advantages. Geosynthetics have proven to be among the most versatile and cost-effective ground modification materials. Their usages have expanded rapidly into nearly all areas of civil, geotechnical, environmental, coastal, and hydraulic engineering. Each of the applications is discussed below.
Geosynthetics in Roadways
Geosynthetics is a planar product manufactured from polymeric material used with soil, rock, earth, or other geotechnical engineering-related material as an essential part of a man-made project, structure, or system. These products or materials can be used, often in conjunction with natural materials, for an enormous variety of purposes, including all surfaces of the transportation industry, including roadways, airports, railroads, and waterways. The main functions performed by geosynthetics are filtration, drainage, separation, reinforcement, provision of a fluid barrier, and environmental protection. Some geosynthetics are used to separate distinct materials, such as different types of soil, so that both can remain completely intact.
Geomembranes are essentially impermeable polymeric sheets used as barriers for liquid or solid waste containment. Geogrids are stiff or flexible polymer grid-like sheets with large openings used primarily as reinforcement of unstable soil and waste masses. Geonets are stiff polymer net-like sheets with in-plane openings used primarily as a drainage material within landfills. Geosynthetic clay liners are manufactured bentonite clay layers merged between geotextiles and/or geomembranes and used as a barrier for liquid or solid waste containment. Geo pipes are perforated or solid wall polymeric pipes used for the drainage of various liquids. Geocomposites are hybrid systems of any, or all, of the above geosynthetic types, which can function as specifically designed for use in soil, rock, waste, and liquid related problems. Geofoams are lightweight blocks, which act as void filling materials in certain construction applications.
The geosynthetic products most commonly used in roadway systems include geotextiles (woven and non-woven) and geogrids (biaxial and multiaxial), although erosion-control products, geocells, geonets (or geocomposite drainage products), and geomembranes have also been incorporated in several applications. These various types of geosynthetics can be used to fulfill one or more specific functions in a variety of roadway applications. For example, geosynthetics have been in use since the 1970s to improve the performance of unpaved roads on soft subgrade soils. Beginning in the 1980s, geosynthetics were utilized to minimize reflective cracking in asphalt overlays as well as to improve the performance of base aggregate layers
Geosynthetics in the Drainage system
Geosynthetics can be effectively used as drains and filters in civil and environmental works in addition to or in substitution to traditional granular materials. Geosynthetics are easier to install in the field and often cost-effective in situations were granular materials available do not meet design specifications, are scarce, or have their use restricted by environmental legislation. Conventional graded granular materials are used for filtration and drainage purpose in various projects of civil engineering. Various types of aggregate drains are available. The most common form of aggregate filled drains is the French drain which comprises a trench filled with free-draining aggregates.
Satisfying the drainage criterion for conventional graded filter design is extremely expensive. The conditions can easily and cheaply be achieved using a geosynthetic drainage system. It can perform both drainage and filtration. Geosynthetic allows water to pass along its plane. Transmissivity. Filtration: Geosynthetic also allows water to pass across its plane, but retain the soil particles
Geosynthetics in Sandy and Muddy Coastal Management
Geotextile tube is one of the geosynthetics structures that are increasingly used in coastal protection. Geotextile tubes are made from high-strength geosynthetic fabrics that allow the water to flow through pores while retaining the filling materials. They are widely used for dewatering, flood control, and coastal protection. Geotextile tubes can be used in various conditions as a result of the low consumption of construction cost and time, the requirement of simple equipment, and low-skilled workers. Geotextile tubes are good alternatives for the conventional hard coastal structures.
However, they have lower resistance to wave attacks. Also, the design code is insufficient for geotextile tube applications. Sandy beaches and mudflats are two types of the geotechnical stratum of the coasts. The morphological characteristics of sandy coasts and mudflats vary due to the variation in wave propagation towards the beach. For example, sandy beaches are continually reshaped by higher intensity waves and tides. Fine sand will be washed away and leave coarse sand to withstand the wave forces. On the other hand, mudflats that are composed of sand, clay, or fine silt occur at the coastlines which are protected from strong waves. Finally, lower wave energy allows the deposition of fine particles which further leads to the formation of the mudflat. In many tropical countries, mangroves grow along the muddy coast. Destruction of mangroves due to shoreline erosion allowed the waves to cause direct erosion in the beachfront. Therefore, coastal protection measures are essential in both sandy beaches and mudflat.
Geosynthetics in slope stabilization
Geotextile has been used successfully on numerous occasions to stabilize steep slope in residual soil and weathered rock. Geotextile was used as tensile reinforcement and filter to stabilize slopes or embankments. The geotextile is usually placed in horizontal layers within the slope. It is placed along with the slope cutting across potential sliding surfaces in the soil. The geotextile will reduce the pore water pressure within the slopes during the rainy season, thereby increasing the shear strength. The geotextile also acts as a filter that prevents the migration of soil or sometimes called the internal erosion within the slope. Last but not least, the geotextile reinforces the soil along potential sliding zones or planes. All these will increase the stability of the slope.
Many factors are attributing to the selection of geotextile in geotechnical engineering. The first fundamental reason is that there is a need for membrane-like materials because geotechnical structures are built with granular materials; the integrity of layers of granular soils can be disrupted by erosion, settlements and earthquakes while a geotextile layer remains continuous. Besides, geotextile is bi-dimensional and flexible materials and is well-suited to geotechnical structures subjected to different movements. Geotextiles are also useful, either as an interface between layers or as a liner or protection at the surface of the mass geotechnical structures. In addition to the factors mentioned above, geotextiles have been successful because manufacturers have aggressively developed and marketed them, and because contractors, designers and owners have elected to use them. Reasons attributing to the selection of geotextile application in geotechnical engineering by contractors, designers and owners.
Geosynthetics in Landfills
The cover system of the landfill illustrated in the figure contains a composite geomembrane/GCL barrier layer. The drainage layer overlying the geomembrane is a geocomposite sheet drain (composite geotextile/geonet). Besides, the soil cover system includes geogrid, geotextile, or geocell reinforcements below the infiltration barrier system. This layer of reinforcements may be used to minimize the strains that could be induced in the barrier layers by differential settlements of the refuse or by future vertical expansion of the landfill. Also, the cover system could include a geogrid or geotextile reinforcement above the infiltration barrier to provide stability to the vegetative cover soil. Fiber reinforcement may also be used for stabilization of the steep portion of the vegetative cover soil. A geocomposite erosion control system above the vegetative cover soil is indicated in the figure and protects against sheet and gully erosion.
Geosynthetics used in landfills provide technical and economic advantages over traditional clay liners. It may create stability issues and even lead to landfill failure due to its low interface or internal shear strength if improperly designed and/or constructed. The most common failure mechanism in geosynthetic-lined landfills is transitional failure involving waste and bottom liner (deep-seated failure) or only final cover system (shallow failure). Shear strengths of geosynthetic-geosynthetic and geosynthetic-soil have a wide range of variations.
Geosynthetics in water management
Geosynthetics also are used to line holding ponds for shrimp and fish in large aquaculture farms. The lined ponds have many advantages over standard soil or clay-lined ponds including decreased permeability and ease of cleaning and harvesting. The low permeability membranes ensure that more water stays in the ponds. It also assures that disease, should it occur, is not allowed to migrate through the subsurface soils and contaminate other ponds.
There is a wide range of applications in which geosynthetics are being used successfully to improve the process of storing and treating water and wastewater. The applications include decorative ponds, potable water storage, and wastewater treatment lagoons. Geosynthetics have lower permeability and generally are less expensive and easier to install than alternative liners.
Geosynthetics in Erosion and Sediment Control
Geosynthetics replace traditional materials such as soil and stone in performing important engineering functions and thus can be selected via a “design-by-function” methodology as prescribed by Koerner (2012). While traditional applications of geosynthetics perform more common in-ground functions such as separation and filtration, geosynthetics used in erosion and sediment controls are used on the soil surface. As such, they introduce the following unique functions according to ASTM D5819:
There are two categories of erosion control systems: The first is termed temporary or degradable and the second is termed long-term or nondegradable. There are numerous types of materials within these categories according to Zoghi, et al, (2000). Temporary degradable systems include conventional loose mulches, as well as, hydraulic mulch geofibers (HMG), erosion control netting (ECN), open weave meshes (ECM), erosion control blankets (ECB), and fiber roving systems (FRS). The long-term systems include conventional sod and riprap, as well as, turf reinforcement mats (TRM), fabric formed revetments (FFR), geocellular confinement systems (GCS), gabions (G), and articulating concrete blocks (ACB). ECNs, ECMs, ECBs, and TRMs commonly contain geosynthetic components and are classified as rolled erosion control products, or RECPs. Other geosynthetic systems include FFRs and GCSs.
Source – innovation textiles.com, sciencedirectassets.com, nptel.ac.in, ejge.com, geosyntheticssociety.org, erosiontest.com/