Geogrid

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Geogrids1.jpg
Geogrids are used to prevent sliding on long and steep slopes during installation and use of a landfill capping system. Geogrid on a slope.jpg
Geogrids are used to prevent sliding on long and steep slopes during installation and use of a landfill capping system.

A geogrid is geosynthetic material used to reinforce soils and similar materials. Soils pull apart under tension. Compared to soil, geogrids are strong in tension. This fact allows them to transfer forces to a larger area of soil than would otherwise be the case.[ citation needed ]

Contents

Geogrids are commonly made of polymer materials, such as polyester, polyvinyl alcohol, polyethylene or polypropylene. They may be woven or knitted from yarns, heat-welded from strips of material, or produced by punching a regular pattern of holes in sheets of material, then stretched into a grid.

The development of methods of preparing relatively rigid polymeric materials by tensile drawing, [2] in a sense "cold working," raised the possibility that such materials could be used in the reinforcement of soils for walls, steep slopes, roadway bases and foundation soils. The principal function of geogrids is for reinforcement. This area, as with many other geosynthetics, is very active, with a number of different products, materials, configurations, etc., making up today's geogrid market. The key feature of all geogrids is that the openings between the adjacent sets of longitudinal and transverse ribs, called “apertures,” are large enough to allow for soil strike-through from one side of the geogrid to the other. The ribs of some geogrids are often quite stiff compared to the fibers of geotextiles. As discussed later, not only is rib strength important, but junction strength is also important. The reason for this is that in anchorage situations the soil strike-through within the apertures bears against the transverse ribs, which transmits the load to the longitudinal ribs via the junctions. The junctions are, of course, where the longitudinal and transverse ribs meet and are connected. They are sometimes called “nodes”.

Currently there are three categories of geogrids. The first, and original, geogrids (called unitized or homogeneous types, or more commonly referred to as 'punched and drawn geogrids') were invented by Dr Frank Brian Mercer [3] in the United Kingdom at Netlon, Ltd., and were brought in 1982 to North America by the Tensar Corporation. A conference in 1984 was helpful in bringing geogrids to the engineering design community. [4] A similar type of drawn geogrid which originated in Italy by Tenax is also available, as are products by new manufacturers in Asia.

The second category of geogrids are more flexible, textile-like geogrids using bundles of polyethylene-coated polyester fibres as the reinforcing component. They were first developed by ICI Linear Composites LTD in the United Kingdom around 1980. This led to the development of polyester yarn geogrids made on textile weaving machinery. In this process hundreds of continuous fibers are gathered together to form yarns which are woven into longitudinal and transverse ribs with large open spaces between. The cross-overs are joined by knitting or intertwining before the entire unit is protected by a subsequent coating. Bitumen, latex, or PVC are the usual coating materials. Geosynthetics within this group are manufactured by many companies having various trademarked products. There are possibly as many as 25 companies manufacturing coated yarn-type polyester geogrids on a worldwide basis.

The third category of geogrids are made by laser or ultrasonically bonding together polyester or polypropylene rods or straps in a gridlike pattern. Two manufacturers currently make such geogrids.

The geogrid sector is extremely active not only in manufacturing new products, but also in providing significant technical information to aid the design engineer.

Ecological balance

Usually retaining walls are constructed of reinforced concrete, if an impermeable surface is not desired, it would be a sensible solution to create a filling area (but not for dam constructions). Choosing the ground reinforced with geogrid reinforcements instead of reinforced concrete retaining wall will also contribute to the ecological balance. While reinforced concrete wall surfaces cannot be vegetated, the surfaces of filled areas reinforced with geogrid reinforcements can be vegetated. [5]

Applications of Geogrids

Geogrids are extensively utilised across a diverse range of civil engineering projects, spanning from power generation and soil stabilisation to erosion control and roadway improvement. In addressing the challenges inherent in land construction, geogrids emerge as a natural and cost-effective solution for subgrade development. Civil engineers must consider various factors depending on the land being developed. At Strata Geosystems, we are committed to providing assistance throughout the planning and consultation process. Some common applications of geogrids are:

1. Pavements: Geogrids have been effectively employed in pavement and roadway construction for the past two decades. Their applications include sub-grade improvement, reinforcing the base course, sub-base, and surface courses. By reinforcing pavements with geogrids, the outward displacement of railway ballast is arrested, and settlement is significantly reduced. This reinforcement is particularly beneficial in clayey compressive soils, as it enhances the California Bearing Ratio (CBR) of sub-grade soil composites. Stiffer geogrids demonstrate superior performance in soft sub-grade conditions compared to flexible geogrids, which tend to react quickly to applied loads.

2. Retaining walls: In retaining wall applications, geogrids are utilised to stabilise the backfill material. The stability of earth-retaining walls is influenced by the friction angle, and the performance of geogrids is affected by their creep and stress relaxation properties. It is essential to ensure that the working stress does not exceed 40% of the geogrid's strength. High-strength geogrids should be placed in the middle of the retaining wall, or the spacing of the geogrid reinforcement should be reduced to enhance stability. This reinforcement helps increase the bearing and energy absorption capacities of the wall, particularly when dealing with marginal backfills.

3. Foundations in soft soil: Geogrids are crucial in foundation applications, particularly in soft soil conditions, where they provide the necessary stiffness and stability to act as reinforcement. Both uniaxial and biaxial geogrids are commonly used in foundation works. The effectiveness of geogrids in enhancing stability is largely dependent on their interlocking capacity with aggregates. Studies have shown that the bearing capacity of circular rigid foundations increases significantly with the use of geogrid reinforcement, especially when multiple layers are employed.

4. Slope stability: Geogrids play a vital role in enhancing slope stability by influencing slope deformation and overall stability. Research indicates that the addition of geogrid reinforcement can improve load-settlement behavior and bearing capacity at selected locations within the slope. The effectiveness of geogrids in slopes is contingent upon factors such as length, edge distance, and particle size. While longer geogrids can increase costs, they also enhance the safety factor of earthen embankments by reducing displacement under loading conditions.

5. Concrete structures: In structural applications, geogrids serve as additional reinforcement and shear reinforcement, significantly improving the load-bearing capacity of concrete components. The use of fibers such as polypropylene and steel in conjunction with geogrids enhances strength and energy absorption while reducing slippage, shear, and bond strength. Geogrids are particularly effective in thin concrete layers and prefabricated structures, providing resistance to chemicals, corrosion, and temperature variations. Their incorporation into structural elements leads to improved overall performance and durability. [6]

Related Research Articles

<span class="mw-page-title-main">Geotechnical engineering</span> Scientific study of earth materials in engineering problems

Geotechnical engineering, also known as geotechnics, is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles of soil mechanics and rock mechanics to solve its engineering problems. It also relies on knowledge of geology, hydrology, geophysics, and other related sciences.

<span class="mw-page-title-main">Masonry</span> Building of structures from individual units of stone, bricks, or blocks

Masonry is the craft of building a structure with brick, stone, or similar material, including mortar plastering which are often laid in, bound, and pasted together by mortar. The term masonry can also refer to the building units themselves.

<span class="mw-page-title-main">Retaining wall</span> Artificial wall used for supporting soil between two different elevations

Retaining walls are relatively rigid walls used for supporting soil laterally so that it can be retained at different levels on the two sides. Retaining walls are structures designed to restrain soil to a slope that it would not naturally keep to. They are used to bound soils between two different elevations often in areas of inconveniently steep terrain in areas where the landscape needs to be shaped severely and engineered for more specific purposes like hillside farming or roadway overpasses. A retaining wall that retains soil on the backside and water on the frontside is called a seawall or a bulkhead.

Fibre-reinforced plastic is a composite material made of a polymer matrix reinforced with fibres. The fibres are usually glass, carbon, aramid, or basalt. Rarely, other fibres such as paper, wood, boron, or asbestos have been used. The polymer is usually an epoxy, vinyl ester, or polyester thermosetting plastic, though phenol formaldehyde resins are still in use.

Basalt fibers are produced from basalt rocks by melting them and converting the melt into fibers. Basalts are rocks of igneous origin. The main energy consumption for the preparation of basalt raw materials to produce of fibers is made in natural conditions. Basalt fibers are classified into 3 types: Basalt continuous fibers (BCF), used for the production of reinforcing materials and composite products, fabrics, and non-woven materials; Basalt staple fibers, for the production of thermal insulation materials; and Basalt superthin fibers (BSTF), for the production of high quality heat- and sound-insulating and fireproof materials.

<span class="mw-page-title-main">Geosynthetics</span> Synthetic material used to stabilize terrain

Geosynthetics are synthetic products used to stabilize terrain. They are generally polymeric products used to solve civil engineering problems. This includes eight main product categories: geotextiles, geogrids, geonets, geomembranes, geosynthetic clay liners, geofoam, geocells and geocomposites. The polymeric nature of the products makes them suitable for use in the ground where high levels of durability are required. They can also be used in exposed applications. Geosynthetics are available in a wide range of forms and materials. These products have a wide range of applications and are currently used in many civil, geotechnical, transportation, geoenvironmental, hydraulic, and private development applications including roads, airfields, railroads, embankments, retaining structures, reservoirs, canals, dams, erosion control, sediment control, landfill liners, landfill covers, mining, aquaculture and agriculture.

<span class="mw-page-title-main">Concrete slab</span> Flat, horizontal concrete element of modern buildings

A concrete slab is a common structural element of modern buildings, consisting of a flat, horizontal surface made of cast concrete. Steel-reinforced slabs, typically between 100 and 500 mm thick, are most often used to construct floors and ceilings, while thinner mud slabs may be used for exterior paving.

<span class="mw-page-title-main">Geotextile</span> Textile material used in ground stabilization and construction

Geotextiles are versatile permeable fabrics that, when used in conjunction with soil, can effectively perform multiple functions, including separation, filtration, reinforcement, protection, and drainage. Typically crafted from polypropylene or polyester, geotextile fabrics are available in two primary forms: woven, which resembles traditional mail bag sacking, and nonwoven, which resembles felt.

Landscape products are a group of building industry products used by garden designers and landscape architects and exhibited at trade fairs devoted to these industries. They include: walls, fences, paving, gardening tools, outdoor lighting, water features, fountains, garden furniture, garden ornaments, gazebos, garden buildings, and pond liners.

<span class="mw-page-title-main">Geocomposite</span> Composite material made up of multiple geosynthetic components.

Geocomposites are combinations of two or more geosynthetic materials for civil engineering applications that perform multiple geosynthetic functions; the five basic functions are: separation, reinforcement, filtration, drainage, and containment. Such composite materials may enhance technical properties of the soil or the geotechnical structure and minimize application costs.

Olefin fiber is a synthetic fiber made from a polyolefin, such as polypropylene or polyethylene. It is used in wallpaper, carpeting, ropes, and vehicle interiors.

Fiber-reinforced concrete or fibre-reinforced concrete (FRC) is concrete containing fibrous material which increases its structural integrity. It contains short discrete fibers that are uniformly distributed and randomly oriented. Fibers include steel fibers, glass fibers, synthetic fibers and natural fibers – each of which lend varying properties to the concrete. In addition, the character of fiber-reinforced concrete changes with varying concretes, fiber materials, geometries, distribution, orientation, and densities.

<span class="mw-page-title-main">Technical textile</span> Textile product valued for its functional characteristics

"Technical textile" refers to a category of textiles specifically engineered and manufactured to serve functional purposes beyond traditional apparel and home furnishing applications. These textiles are designed with specific performance characteristics and properties, making them suitable for various industrial, medical, automotive, aerospace, and other technical applications. Unlike conventional textiles used for clothing or decoration, technical textiles are optimized to offer qualities such as strength, durability, flame resistance, chemical resistance, moisture management, and other specialized functionalities to meet the specific needs of diverse industries and sectors.

<span class="mw-page-title-main">Soil nailing</span> Remedial construction measure

Soil nailing is a remedial construction measure to treat unstable natural soil slopes or unstable man-made (fill) slopes as a construction technique that allows the safe over-steepening of new or existing soil slopes. The technique involves the insertion of relatively slender reinforcing elements into the slope – often general purpose reinforcing bars (rebar) although proprietary solid or hollow-system bars are also available. Solid bars are usually installed into pre-drilled holes and then grouted into place using a separate grout line, whereas hollow bars may be drilled and grouted simultaneously by the use of a sacrificial drill bit and by pumping grout down the hollow bar as drilling progresses. Kinetic methods of firing relatively short bars into soil slopes have also been developed.

<span class="mw-page-title-main">Mechanically stabilized earth</span> Soil constructed with artificial reinforcing

Mechanically stabilized earth is soil constructed with artificial reinforcing. It can be used for retaining walls, bridge abutments, seawalls, and dikes. Although the basic principles of MSE have been used throughout history, MSE was developed in its current form in the 1960s. The reinforcing elements used can vary but include steel and geosynthetics.

Landslide mitigation refers to several human-made activities on slopes with the goal of lessening the effect of landslides. Landslides can be triggered by many, sometimes concomitant causes. In addition to shallow erosion or reduction of shear strength caused by seasonal rainfall, landslides may be triggered by anthropic activities, such as adding excessive weight above the slope, digging at mid-slope or at the foot of the slope. Often, individual phenomena join to generate instability over time, which often does not allow a reconstruction of the evolution of a particular landslide. Therefore, landslide hazard mitigation measures are not generally classified according to the phenomenon that might cause a landslide. Instead, they are classified by the sort of slope stabilization method used:

<span class="mw-page-title-main">Cellular confinement</span> Confinement system used in construction and geotechnical engineering

Cellular confinement systems (CCS)—also known as geocells—are widely used in construction for erosion control, soil stabilization on flat ground and steep slopes, channel protection, and structural reinforcement for load support and earth retention. Typical cellular confinement systems are geosynthetics made with ultrasonically welded high-density polyethylene (HDPE) strips or novel polymeric alloy (NPA)—and expanded on-site to form a honeycomb-like structure—and filled with sand, soil, rock, gravel or concrete.

A geonet is a geosynthetic material similar in structure to a geogrid, consisting of integrally connected parallel sets of ribs overlying similar sets at various angles for in-plane drainage of liquids or gases. Geonets are often laminated with geotextiles on one or both surfaces and are then referred to as drainage geocomposites. They are competitive with other drainage geocomposites having different core configurations.

Novel polymeric alloy (NPA) is a polymeric alloy composed of polyolefin and thermoplastic engineering polymer with enhanced engineering properties. NPA was developed for use in geosynthetics. One of the first commercial NPA applications was in the manufacturer of polymeric strips used to form Neoloy® cellular confinement systems (geocells).

The Neoloy Geocell is a Cellular Confinement System (geocell) developed and manufactured by PRS Geo-Technologies Ltd. Geocells are extruded in ultrasonically welded strips. The folded strips are opened on-site to form a 3D honeycomb matrix, which is then filled with granular material. The 3D confinement system is used to stabilize soft subgrade soil and reinforce the subbase and base layers in flexible pavements. Cellular confinement is also used for soil protection and erosion control for slopes, including channels, retention walls, reservoirs and landfills.

References

  1. ↑ Müller, W. W.; Saathoff, F. (2015). "Geosynthetics in geoenvironmental engineering". Science and Technology of Advanced Materials. 16 (3): 034605. Bibcode:2015STAdM..16c4605M. doi:10.1088/1468-6996/16/3/034605. PMC   5099829 . PMID   27877792.
  2. ↑ Capaccio, G.; Ward, I. M. (1973). "Properties of Ultra-high Modulus Linear Polyethylenes". Nature Physical Science. 243 (130): 143. Bibcode:1973NPhS..243..143C. doi: 10.1038/physci243143a0 .
  3. ↑ Mercer, F.B. (1987) "Critical Aspects of Industrial and Academic Collaboration," The Philips Lecture, The Royal Society.
  4. ↑ Ward, I. M. (1984) “The Orientation of Polymers to Produce High Performance Materials” Proceedings of the Symposium on Polymer Grid Reinforcement in Civil Engineering, Institution of Civil Engineers, UK.
  5. ↑ Kırmızı, M. (2020). Stability of filling areas: example of The Çamlica mosque (Doctoral thesis, Istanbul Aydın University, Turkey).
  6. ↑ Applications_and_Performance_of_Geogrids_in_Structures
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