Geosynthetics used to be called geotextiles and geomembranes. With the need of engineering, new varieties of this kind of materials appear constantly, such as geogrid, geotextile and geotextile bag, geotextile pad, geotextile belt, composite geomembrane, bentonite waterproof blanket, composite drainage network and so on. The original name cannot accurately cover all products, so in the following period, they are called "geotextiles, geomembranes and related pus pipes". Obviously, such a name should not be used as a technical term or academic term. Therefore, at the 5th international symposium on geosynthetics held in Singapore in 1994, the name of this material was officially defined as "geosynthetics".
The raw material of geosynthetics is polymer. They are made of chemicals extracted from coal, oil, natural gas or limestone, and then further processed into fiber or synthetic material sheets, and finally made into various products. The polymers used to make geosynthetics mainly include polyethylene (PE), polyester (PET), polyamide (PER), polypropylene (PP), polyvinyl chloride (PVC), chlorinated polyethylene (CPE) and polystyrene (EPS). Geotextile is another name for geotextile. Early products were few, which meant cloth materials used in geotechnical engineering.
In the process of geotextile manufacturing, polymer raw materials are first processed into silk, short fiber, yarn or strip, and then geotextile with plane structure is made. Geotextiles can be divided into woven geotextiles and nonwoven geotextiles according to their manufacturing methods. Woven geotextile is composed of two groups of parallel orthogonal or oblique warp and weft interwoven. Nonwoven geotextile is made by orienting or randomly arranging fibers and then processing them. According to different fiber bonding methods, it can be divided into three bonding methods: chemical bonding, thermal bonding and mechanical bonding.
The outstanding advantages of geotextile are light weight, good overall continuity (large area can be made), convenient construction, high tensile strength, good corrosion resistance and microbial erosion resistance. The disadvantage is that it has not been specially treated and its anti-ultraviolet ability is low. If it is exposed to the sun, direct ultraviolet radiation is easy to age, but if it is not exposed to the sun directly, the anti-aging and durability are still very high. Geomembrane can be generally divided into asphalt and polymer (synthetic polymer). Geomembrane containing asphalt is mainly composite (including woven or nonwoven geotextile), and asphalt is used as wetting binder. Polymer geomembrane can be divided into plastic geomembrane, elastic geomembrane and composite geomembrane according to different main materials.
A large number of engineering practices show that geomembrane has good impermeability, strong elasticity and deformation adaptability, can adapt to different construction conditions and working stresses, and has good aging resistance, especially its durability in underwater and soil. Geomembrane has outstanding anti-seepage and waterproof properties. 1. density: the density depends on the materials that make it up. Even if the polymers used to make geomembrane belong to the same class, there are often obvious differences. For example, polyethylene can be divided into different categories such as ultra-low density, low density, medium density and high density, so the density of PE geomembrane made of it is different. The density of geomembrane polymer ranges from 0.85 mg/l to 1.50 mg/l, and the density commonly used in engineering is generally above 0.94 mg/l. ..
2. Thickness: Thickness refers to the distance from the top surface to the bottom surface of the membrane under the normal pressure of 20kPa. For smooth geomembrane (no embossing or pattern on the surface), the thickness measurement method is similar to that of geotextile, but it should be measured with a higher precision dial indicator. Each sample is measured at least at three different positions, and the average value is taken as the thickness of PE composite geomembrane. Geogrid is a main geosynthetics, which has unique performance and efficacy compared with other geosynthetics. Geogrids are usually used as reinforcing materials for reinforced earth structures or composite materials. Geogrids are divided into glass fiber and polyester fiber.
(1) plastic
This kind of geogrid is a square or rectangular polymer net formed by stretching, which can be divided into uniaxial stretching and biaxial stretching according to the different stretching directions during manufacturing. It is made by punching holes in the extruded polymer sheet (mostly made of polypropylene or high-density polyethylene) and then directionally stretching it under heating conditions. The unidirectional tensile mesh is only manufactured along the length direction of the board, while the bidirectional tensile mesh is manufactured by continuously stretching the unidirectional tensile mesh in the direction perpendicular to its length.
In the manufacturing process of geogrids, polymers will be rearranged and oriented with the heating and stretching process, which will strengthen the binding force between molecular chains and achieve the purpose of improving their strength. Its elongation is only 10% ~ 15% of the original board. If anti-aging materials such as carbon black are added to the geogrid, it will have better durability such as acid resistance, alkali resistance, corrosion resistance and aging resistance.
(2) Glass fiber
This kind of geogrid is made of high-strength glass fiber, and sometimes it is impregnated with self-adhesive pressure glue and surface asphalt, so that the geogrid is closely combined with asphalt pavement. Because the interlocking force between soil and stone in geogrid grid increases, the friction coefficient between them increases significantly (up to 0.8 ~ 1.0), and because of the strong frictional engagement between geogrid and soil, the pull-out force of geogrid buried in soil increases significantly, so it is a good reinforcement material.
At the same time, geogrid is a kind of light and flexible plane net material, which is easy to cut and connect on site, and can also be overlapped. The construction is simple, and special construction machinery and professional technicians are not needed. 1 geomembrane bag
Geomembrane bag is a kind of continuous (or separated) bag-like material made of double-layer polymeric chemical fiber fabric. Concrete or mortar is poured into the membrane bag with a high-pressure pump to form a plate-shaped or other-shaped structure, which is often used for slope protection or other foundation treatment projects. According to the different materials and processing technology, thin film bags can be divided into two categories: mechanical and simple. Machine-made membrane bags can be divided into filtration drainage point membrane bags, non-filtration drainage point membrane bags, non-drainage point concrete membrane bags and hinge block membrane bags according to whether there is filtration drainage point or not and the inflated shape.
2 Earthwork network
Geotextiles are made of synthetic material strips, thick strands woven or synthetic resin pressed, with large holes and high rigidity. Plan 12? Schematic structure of geocell or three-dimensional network geosynthetics. Used for soft foundation reinforcement cushion, slope protection, grass planting and as a base material for manufacturing composite geotechnical materials.
3 Geonet Pad and Geocell
Geonet mat and geocell are three-dimensional structures made of synthetic materials. The former is mostly a three-dimensional permeable polymer mesh pad made of filaments, while the latter (Figure 12? 2) It is a honeycomb or grid-like three-dimensional structure composed of geotextile, geogrid or geomembrane and strip polymer, which is often used in erosion prevention and soil and water conservation projects. Geocell has high rigidity and lateral restraint capacity, and is mainly used for foundation reinforced cushion, foundation bed or ballast bed.
4 polystyrene foam (EPS)
Styrofoam (EPS) is an ultra-light geosynthetic material. It is made by adding foaming agent into polystyrene, pre-foaming according to the specified density, and then drying the foamed particles in a silo and putting them into a mold for heating. EPS has the advantages of light weight, heat resistance, good compression resistance, low water absorption and good self-reliance, and is often used as a filler for railway subgrade. Geotextiles, geomembranes, geogrids and some special geosynthetics are combined with each other to become geosynthetics. Geotechnical composites can combine the properties of different materials to better meet the needs of specific projects and can play a multi-functional role. For example, composite geomembrane is a geotextile composition made of geomembrane and geotextile according to certain requirements. Among them, geomembrane is mainly used for seepage control, and geotextile plays the role of reinforcement, drainage and increasing the friction between geomembrane and soil surface. Another example is geotechnical composite drainage material, which is composed of nonwoven geotextiles and geotextiles, geomembranes or geosynthetics with different shapes. It is used for drainage and consolidation treatment of soft foundation, vertical and horizontal drainage of subgrade, underground drainage pipes of buildings, collecting wells, drainage behind walls of enclosure buildings, tunnel drainage, dam drainage facilities, etc. The plastic drainage board commonly used in subgrade engineering is a kind of geotechnical composite drainage material.
The geotechnical composite materials widely used in foreign roads are glass fiber polyester anti-crack cloth and warp-knitted composite reinforced anti-crack cloth. It can prolong the service life of roads, thus greatly reducing the maintenance and maintenance costs. Considering the long-term economic benefits, China should actively adopt and advocate geosynthetics. Geosynthetics, different products have different characteristics and can be used in many engineering fields.
It has been applied to geotechnical engineering, civil engineering, water conservancy engineering, environmental engineering, traffic engineering, municipal engineering and land reclamation engineering.
Protection:
Soil erosion is a natural process caused by water power and wind power, which is influenced by many factors such as soil, vegetation and landform. Under certain conditions, human life activities will also accelerate this process. If this kind of erosion is not treated properly, it may cause great damage to existing buildings and environment.
In terms of soil erosion control, geosynthetics can be applied to slope protection, water conveyance channel protection, coastline protection, beach reclamation, vegetation restoration, rockfall protection net and flood control dam construction. According to the engineering characteristics and site conditions, the erosion control project may involve one or more geosynthetics products.
In slope protection engineering, in addition to some geosynthetics, soil nails and even rock anchors are needed to ensure the stability of the protection system. In some cases, geotextile bags filled with mortar will be used to fix the protective surface, and grass seeds will be inserted into the gaps of the protective structure to cultivate vegetation to prevent soil erosion.