Long ago, when difficult sites were settled for construction purposes, traditional practice was limited to either the replacement of unsuitable soil or the adoption of suitable foundations, which sometimes increased the cost of the foundation. Innovative soil amendment approaches have been developed to solve soil related problems. One of them is the use of geosynthetics. They have the following advantages when used to increase the strength of soil.
- They are space saving
- Better material quality control,
- Better build quality control,
- cost savings,
- technical superiority,
- saving construction time,
- content deployment,
- material availability,
- environmental sensitivity.
Different types of geosynthetics
10 different types of geosynthetics are given below.
Geo-textile is actually cloth in a traditional sense, but it consists of synthetic fibers instead of natural fibers such as cotton, wool and silk. So biodegradation is not a problem. The key point is that they are porous to water flow in their built plane and also within their plane, but to widely varying degrees. Geotextile is manufactured from polymer polyester or polypropylene. Polypropylene is a lighter material than water (its specific gravity is 0.9). It is considered strong and very durable. The polyester used is heavier than water and gives it excellent strength and creep properties. There are two types of geotextiles. They are woven and non-woven geotextiles. Woven threads and non-woven geotextiles are manufactured using polypropylene filaments and staple fibers. Non-woven types are manufactured from staple fiber. They are typically 1 to 4 inches in length or a continuous filament that is randomly distributed in layers on a moving belt to create a “web”-like feel. It is mainly used as a surface drainage. Woven geotextiles are made by weaving monofilament, multifilament or slit film yarns. Slit film yarns are further classified into flat tape and fibrillated yarns. There are two steps in the process of making woven garments. They are manufacturing filaments and weaves. Slit films are used in sediment control and road stabilization works, but are a poor choice for sub-surface drainage and erosion control works because of their low permeability. Optically fabrics made from fibrillated tape yarns have better uniform openings and permeability than flat tapes.
Geo-grids are plastics formed into a very open mesh-like configuration. Single or multi-layer materials are usually made by extruding and stretching high density polyethylene or by weaving or weaving polypropylene. The resulting grid structure has large openings called apertures. These pores enhance the interaction with soil and aggregates. It is a good soil and composite reinforcement due to its good tensile strength and hardness.
Geonets are stacked criss-crossing polymer strands that provide in-plane drainage. Geonets are all made of polyethylene. The molten polymer is extruded through slits in the counter-rotating die that form a matrix or a mesh of closely spaced “stacked” strands. When the strand has two layers it is called “biplanar” and when the strand has three layers it is called “triplanar”.
Geocomposites are geotextile filters surrounding the geonet. Some of the functions of geocomposites are as blanket drain, panel drain, edge drain and wick drain. Blanket drains are commonly used as leachate, infiltration collection, removal layers within landfills. Panel drains are placed adjacent to the structure to reduce hydrostatic pressure. Side drains are used adjacent to pavement structures which helps to collect and remove lateral seepage from the base of the road.
Geomembranes are impermeable thin sheets of rubber or plastic material used primarily for the lining and covering of liquid- or solid-storage barriers. Thus the primary function is always as a liquid or vapor barrier. They are relatively impermeable when compared to clay or geotextiles. They are divided into two general categories, they are calendered and extruded. For the calendered type, the materials used are polyvinylchloride, chlorosulfonated polyethylene, chlorinated polyethylene, and polypropylene. For the extruded type, the material used is high dense polyethylene.
6. Geosynthetic Clay Liners
Geosynthetic Clay Liners (GCL) consist of a thin layer of finely ground bentonite clay. Soil swells when wet and becomes a very effective hydraulic barrier. GCL is manufactured by sandwiching bentonite inside or by layering it over geotextiles and/or geomembrane. The bonding of the layers is done with sewing, needling and/or chemical adhesives.
Geo-foam is a new category of geosynthetic product. It is a generic name for any foam material used for geotechnical applications. Geofoam is manufactured in large blocks that are stacked to form a lightweight and thermally insulating mass buried within a soil or pavement structure. The most common type of polymer used in the manufacture of geofoam materials is polystyrene. The applications of geofoam are
- It is used within clay embankments built on soft, weak soils
- Used under roads, airspace sidewalks and railway track systems that are subject to extreme freeze-thaw conditions
- Used under on-grade storage tanks containing cold liquids.
Another important product that has been adopted as geosynthetic is plastic pipe. Typical polymer resins used in the manufacture of plastic pipes are high-density polyethylene (HDPE), polyvinyl chloride (PVC), polypropylene (PP), polybutylene (PB), acrylonitrile butadiene styrene (ABS), and cellulose acetate butyrate. Cab). These products are used for a wide variety of civil engineering applications. These include leachate removal system, interceptor drain and highway and railway edge drain.
9. Turf Reinforcement Mats
Turf reinforcement mats (TRMs) are three-dimensional structures composed of fused polymer netting, randomly placed monofilaments, or yarns woven or knotted into an open and dimensionally stable mat. Planting these mats can enhance erosion protection, which can provide more protection than normally grown plants. The proven performance has resulted in widespread use and has ensured the acceptance of TRM as a sustainable, cost-effective and environmentally friendly alternative to hard shell erosion protection solutions such as concrete and riprap.
3-D honeycomb-like structures filled with mud, rock and concrete. They are made of polymer sheets/strips of geotextiles, which are joined at staggered points to form a large honeycomb when its strips are separated. The ground cells were made from a novel polymer alloy called Neoalloy. Geocell with high elastic modulus has the rigidity of reinforced base and high bearing capacity. Geocells made from NPA have been found to be significantly better in rigidity, ultimate bearing capacity and strength relative to HDPE geocells. NPA geocells show better creep resistance and better retention of creep resistance and stiffness, especially at elevated temperatures, as verified by plate load testing and numerical modeling. A full scale research has shown that NPA geocells have a low thermal expansion coefficient and creep reduction factor. It showed a higher tensile stiffness and strength than HDPE geocells and NPA geocells showed increased bearing capacity and significantly reduced settlement of compacted sand base course compared to geocells manufactured from HDPE.