1. Geotextile Properties
Geotextile is a kind of chemical fibre product. Its raw materials include polypropylene (polypropylene), polyester (polyester), polylaurylamine (cotton) and so on. It can be divided into two categories: textile (spinning) fabric and non-textile fabric in terms of product clocks. The so-called textile fabrics are also made from polymers to obtain fibers, which are then woven into planned fabric on looms. The so-called non-woven industrial fabric raw material is polypropylene and other fiber products, so it has the advantages of strong chemical resistance, high melting point, high strength, and so on. Compared with non-woven fabric, non-woven fabric has lower cost, simple process, high output, and no significant direction of its tensile strength. Therefore, non-woven fabric is widely used in the world at present. Geotextiles have different specifications according to their different uses.
2. Function and application of Geotextiles
The functions of geotextiles as building materials are various. The following basic functions and applications have been recognized by experts, designers and manufacturers.
(1) Separation. Geotextiles can effectively prevent the mixing of two different sizes of soil materials, so as to avoid mixing with each other or soil erosion. This function is very important for the construction of road or railway subgrade on soft soil. Experience shows that, in some cases, without geotextiles, it is virtually impossible to build projects on their foundations, because the filling materials will sink directly into the subsoil.
(2) Filtration. Using geotextile as filter layer and graded gravel filter layer can make the same effect. Geotextile can make water flow freely without pressure, but also can prevent the loss of soil fine particles, so as to avoid the instability and erosion of some projects.
A: When geotextile is laid under river blocks or in hydraulic structures, rivers and lake banks are impacted by waves or changes in wave water level. When soil erosion reduces stability, geotextile filter layer is laid between riverbanks and embankments to prevent soil erosion and river bank collapse.
B: Using geotextiles as drainage ditches. Geotextile prevents fine particles from mixing into graded sand-gravel filter layer, so as to avoid blocking and losing the function of graded sand-gravel filter layer and ensure the quality of filter layer.
(3) Drainage. The geotextiles themselves form drainage channels, which collect the water in the soil into the fabric and slowly remove the soil along the fabric.
A: In some tunnel buildings, a waterproof system must be laid between shotcrete shells. The system is composed of impermeable synthetic membranes and geotextiles which act as puncture protection and drainage. Ground water seeping out of rock flows in Geotextiles to drain pipes at the bottom of tunnels, thus preventing water pressure from accumulating behind the water barrier.
B: Highway construction in soft soil areas with large water content can use special machinery to insert geotextiles into the soil. Groundwater flows out of the ground along geotextile columns and into permeable sand or geotextile layers to drain the roadbed.
(4) Reinforcement effect
A: Geotextiles are sandwiched in aggregate-geotextile-soil foundation system, which can disperse vehicle loads to a larger area and reduce the pressure of load on soil foundation. Under the action of load, the deformation of soft soil foundation is embedded in the soil foundation because of the toughness and elongation of geotextiles. Make the whole system form a connection structure, improve the stability of the structure and improve the bearing capacity of the soil foundation.
B: Geotextile is used as retaining wall. Usually concrete is used as retaining wall with high cost and geotextile is used as retaining wall. Its function is to improve the shear strength of soil layer. At the same time, because of the permeability of geotextile, the water seepage from the structure will not accumulate water pressure and enhance the stability of the slope.
Because geotextiles have good physical and mechanical properties, such as isolation, drainage and reinforcement, filter geotextiles also have good hydraulic characteristics, which can not only ensure the free flow of pore water, but also intercept fine particles. Although the application of geotextiles on highways started late, it has achieved good results. Chongqing Highway, Ministry of Communications The Academy of Sciences has preliminarily drawn the following conclusions through calculation, analysis and experimental comparison:
A: Geotextiles are influenced by materials, weaving methods and testing methods. Their strength and properties vary greatly. The application of geotextiles should be analyzed according to the actual situation and selected properly.
B: The main function of Geotextiles in Reinforcing Soft Foundation Embankment is to restrict the lateral displacement of soft foundation and embankment, increase the lateral restraint, thus reducing the stress level and strengthening the stability of embankment. However, the reinforcing effect is affected by such factors as fabric modulus, soft foundation modulus and soft foundation thickness.
C: The reinforcement effect of geotextiles is related to the construction speed. Generally speaking, the construction speed is fast, the reinforcement effect is good, the construction speed is slow, and the reinforcement effect is not significant.
D: Using Duncan model to couple consolidation theory to carry out finite element analysis of practical engineering can basically simulate the actual construction situation and provide a better scheme for the design and construction of major embankments.
E: Geotextiles are simple and easy to use in practical applications. No special equipment is needed. They can be used in any construction site.
3. Treatment of Soft Soil Foundation
After analysis and theoretical calculation, the following treatment methods are adopted for soft soil foundation:
Overload Preloading + Gravel Cushion + Geotextile + Plastic Drainage Plate
Requirements for geotextiles: Tensile stress of e < 10% should be determined according to E-delta curve. Tensile strength of the geotextiles should be greater than 5T/M required by design. Permeable geotextiles should be used.
The plastic drainage board goes deep into the gravel cushion layer of 30 cm. After construction, a layer of geotextiles is laid. The width of geotextiles exceeds 1 m at the foot of the roadbed slope. The geotextiles are covered with 20 cm gravel layer. The geotextiles at both ends are rolled back 1 m inward and compacted with gravel. The lap width of geotextiles shall be no less than 30 cm.