The aperture of geotextiles is an important technical indicator for engineering applications. This article introduces the basic principles of geotextile aperture test
ing and testing standards at home and abroad, and compares and analyzes the methods and related standards. Geotextile is a coiled material for civil engineering made of synthetic fiber weaving or non-woven technology such as cementing, hot pressing and needle punching. It is also called geotextile or geomembrane. Geotextiles can be divided into woven geotextiles, knitted geotextiles, and non-woven geotextiles according to different processing methods . The most commonly used is non-woven geotextile, which is a fibrous structural material formed by consolidating the fiber web by mechanical, chemical, thermal or other methods . The unique fiber three-dimensional network structure of non-woven geotextile makes it have good drainage performance and sand-retaining soil performance, which can replace the traditional sand gravel infiltration layer, which can not only save investment but also shorten the construction period. The important basis for the design and selection of geotextile percolation layer is its water permeability and soil retention performance, and the important characteristic index of these two properties is its pore size. Accurately measuring the hole diameter of the geotextile is conducive to a more reasonable selection of geomaterials in engineering. In this paper, combined with actual work experience, the test methods of geotextile aperture are summarized as follows. One, pore size parameter pore size parameters mainly include effective pore size, characteristic pore size, average pore size, maximum pore size, minimum pore size, bubble point pore size, pore size distribution, porosity, etc. . 1.1 The effective pore diameter (Oe) JTG E50-2006 'Highway Engineering Geosynthetics Test Regulations' is defined as follows: the approximate maximum particle diameter that can effectively pass through the geotextile, for example, O90 means that 90% of the pore diameter in the geotextile is below this value [ 4]. The definition in GB/T 14799-2005 'Determination of the effective pore diameter of geotextiles and related products' is as follows: The effective pore diameter is the approximate maximum particle diameter that can effectively pass through the geotextile. For example, O90 means that 90% of the pore diameters in the geotextile are below this Value . 1.2 The equivalent aperture EOS (or AOS) is defined in the SL/T 235-1999 'Geosynthetics Test Regulations' as follows: Use geotextiles as a sieve cloth to screen and analyze granular materials. When a granular material is passed through When the sieving rate (the ratio of the weight of the particulate material passing through the fabric to the total weight of the particulate material) is 5%, the particle size is determined as the equivalent pore size of the geotextile . GB 50290-1998 'Technical Specification for Geosynthetics Application' and SL/T 225-1998 'Technical Specification for Geosynthetics Application in Water Conservancy and Hydropower Engineering' are defined as follows: the maximum apparent aperture of geotextile [7-8]. JTJ/T 019-1998 'Technical Specifications for the Application of Geosynthetics for Highways' is defined as follows: It is used to indicate the index of the pore size of fabric-type geosynthetics. Using different sieve residue ratio standards, different equivalent pore diameter values u200bu200bcan be obtained . 1.3 Characteristic aperture The hole size of the geotextile is equivalent to the maximum particle size when 90% of the soil particles pass through the geotextile . This definition is suitable for the wet sieve method in the determination of the effective aperture of geotextiles and related products. 1.4 Bubble Point Aperture The gas on one side of the filter cloth passes through the filter cloth to the water on the other side and generates bubbles. This method is used to calculate the filter cloth pore size . 1.5 Maximum bubble point pore size The bubble point pore size when the gas passes through the filter cloth and reaches the water to produce the first series of bubbles . 1.6 Pore size distribution For a given sample, according to the pore diameter distribution, calculate the percentage of pores corresponding to a certain pore size , which can be used to characterize the proportion of different pore sizes in the entire pore size distribution. 1.7 Porosity The ratio of the pore volume of the material to the total volume reflects the index of the degree of geotextile voids, and it is an important factor affecting the hydraulic properties of geotextile permeability . At present, in various standards, the definition of equivalent pore diameter and characteristic pore diameter is basically the same, and the size of the pore is expressed by the size of the particle. The bubble point aperture needs to calculate the equivalent aperture based on the pressure difference when the bubble appears. 2. Pore size test method Geotextile pore size test method is divided into direct method and indirect method, direct method includes microscope method, image analysis method, etc.; indirect method mainly includes dry sieving method, wet sieving method, bubble point method, hydrodynamic method and mercury Pressing method and so on . The principle and evaluation of each method are shown in Table 1. Direct methods such as microscopy. This method is direct, intuitive and reliable. It can directly obtain the number and size of the pores, without changing the original state of the sample, and does not pollute or damage the sample. It is especially suitable for thin fabrics, but the pore distribution on the projection surface cannot reflect the pores inside the fabric Structure, so this method is only suitable for regular fabrics, and the test results have a certain degree of randomness and are not representative.
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