Nonwoven Geotextile Testing

Nonwoven geotextile testing mainly conducts scientific testing and analysis on mass per unit area, thickness, tensile properties, hydraulic properties, durability and friction characteristics, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Mass per unit area: Refers to the mass of the geotextile per unit area, and is a basic indicator for evaluating the uniformity and economy of the material. During testing, the specimen is cut to a specified size and weighed with a balance with an accuracy of 0.01 g for calculation. This parameter directly affects the physical and mechanical properties of the material, and is an important basis for product classification and engineering design.

Thickness: Refers to the thickness of the geotextile under a specified pressure, reflecting its bulkiness and compression characteristics. It is usually measured with a thickness tester under a standard pressure of 2 kPa. The thickness is closely related to the hydraulic and mechanical properties of the material, and is the basis for calculating parameters such as the porosity and permeability coefficient.

Tensile properties: Including breaking strength, elongation at break, trapezoid tearing strength and CBR puncture strength. These indicators comprehensively evaluate the ability of the material to resist damage by external forces during construction and service. The tests are completed on a tensile testing machine in accordance with the wide-width strip method or grab method, simulating the stress states in different directions.

Hydraulic properties: Mainly including the vertical permeability coefficient and the apparent opening size (O90/O95). The vertical permeability coefficient characterizes the water permeability of the material under normal water flow; the apparent opening size reflects its soil retention performance, i.e., the ability to prevent the loss of the protected soil particles. Both are key parameters for filtration and drainage design.

Durability: Evaluates the performance retention rate of the material under long-term environmental action, including resistance to ultraviolet aging, oxidation, acid and alkali. Usually, after artificial accelerated aging tests (such as xenon lamp exposure), the retention rate of its tensile strength is tested to predict its service life.

Friction characteristics: Mainly referring to the interface friction coefficient between the geotextile and the soil (or between the geotextile and the geotextile). Determined by direct shear tests, this parameter is crucial for slope stability and reinforced structure design, directly affecting the safety factor of the project.

Testing Scope

Needle-punched nonwoven geotextiles: Made by interlocking and reinforcing the fibre web through the needle-punching process. Testing needs to focus on its anisotropy, i.e., the difference between the longitudinal and transverse mechanical properties. Its apparent opening size range is wide, and it is widely used in engineering such as filtration, separation and protection.

Thermally bonded nonwoven geotextiles: Made by bonding heat-fusible fibres through heating. During testing, attention needs to be paid to the fact that its thickness is sensitive to temperature. This type of product usually has a smooth surface and uniform mechanical properties, but its performance may decay in high-temperature environments, so durability testing needs to be strengthened.

Chemically bonded nonwoven geotextiles: Made by bonding the fibre web with adhesives. The test items need to add the evaluation of the durability of the adhesive (such as resistance to washing and hydrolysis). Its performance is significantly affected by the type and dosage of the adhesive, and it may involve the testing of environmentally harmful substances.

Products of different grammages and thicknesses: The testing scope covers the full series of products from light types (such as 100 g/m²) to heavy types (such as above 1000 g/m²). For different specifications, the test methods and fixture sizes may need to be adjusted accordingly, to ensure the accuracy and comparability of the data.

Products of different raw material compositions: Mainly including synthetic fibre products such as polyester (PET) and polypropylene (PP). Testing needs to be distinguished according to the raw material characteristics, such as the antioxidant aging performance of polypropylene and the hydrolysis resistance of polyester, which are the respective focuses of durability testing.

Composite nonwoven geotextiles: Such as nonwoven/woven composite geotextiles. The testing scope needs to be extended to the performance of the whole composite material and each of its single components, and to evaluate the interfacial bonding strength, to comprehensively reflect the comprehensive functions of the composite product.

Testing Methods

Mass per unit area determination (weighing method): In accordance with standards such as GB/T 13762 or ISO 9864. Not less than 10 specimens of a specified area (usually 100 cm² or larger) are cut from the full roll sample, conditioned under standard atmospheric conditions, weighed one by one and the average value is calculated, expressed in grams per square metre (g/m²).

Thickness determination (pressure method): In accordance with standards such as GB/T 13761 or ISO 9863. A thickness gauge with a circular base plate and a presser foot that can apply constant pressure is used. The specimen is placed flat on the base plate without tension, the presser foot is lowered to apply a standard pressure of 2 kPa±0.1 kPa, the thickness value is read after a specified time, and multiple points are measured and averaged.

Wide-width tensile test: In accordance with standards such as GB/T 15788 or ISO 10319. The specimen width is 200 mm and the initial distance between the grips is 100 mm. The testing machine stretches the specimen at a constant elongation rate until breakage, and the maximum force and the corresponding elongation are recorded. This method can effectively reduce the "necking" phenomenon, and the results are closer to the actual engineering conditions.

Trapezoid tearing strength test: In accordance with standards such as GB/T 13763 or ISO 9073-4. The specimen is cut into a rectangle, and a cut of a specified length is pre-cut in the center of the short side to form trapezoid wings. The two wings are respectively clamped in the fixtures, and the force required to tear along the cut direction is tested, evaluating the ability of the material to resist the propagation of tearing.

Vertical permeability coefficient test (constant head method): In accordance with standards such as GB/T 15789 or ASTM D4491. The specimen is clamped in a permeameter so that its plane is perpendicular to the water flow direction. A constant head difference is applied, and after the water flow stabilizes, the amount of water permeated within a certain time is measured, and the permeability coefficient is calculated in combination with the area and thickness of the specimen.

Apparent opening size test (dry sieving method): In accordance with standards such as GB/T 14799 or ISO 12956. The specimen is used as a "sieve cloth", placed on a standard sieve frame, and glass beads or standard sand with a known particle size distribution are added, and the sieving is carried out at a specified time and amplitude. By analyzing the particle distribution passed through and retained on the specimen, characteristic opening sizes such as O90 or O95 are determined.

Testing Standards

Domestic Standards:

1. GB/T 15788-2017, Geosynthetics — Wide-width tensile test

2. GB/T 15789-2016, Geotextiles and geotextile-related products — Determination of water flow normal to the surface without load

3. GB/T 14799-2005, Geotextiles and geotextile-related products — Determination of the apparent opening size — Dry sieving method

4. GB/T 13762-2009, Geosynthetics — Test method for mass per unit area of geotextiles and geotextile-related products

5. GB/T 13761-2022, Geosynthetics — Test method for determination of thickness at specified pressures

6. GB/T 13763-2010, Geosynthetics — Test method for trapezoid tearing strength

International Standards:

1. ISO 10319, Geosynthetics — Wide-width tensile test

2. ISO 12956, Geotextiles and geotextile-related products — Determination of the characteristic opening size

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Electronic universal material testing machine: The core equipment for testing mechanical properties such as tension, puncture and tearing. It needs to be equipped with various accessories such as wide-width strip fixtures, grab fixtures, a CBR puncture device and trapezoid tearing fixtures. The equipment should have a high-precision load sensor and displacement measurement system, and the software can automatically calculate and output various strength and elongation data.

Standard pressure thickness gauge: Used to precisely measure the thickness. The presser foot area of the instrument is usually 25 cm² (diameter of about 56.4 mm), and can automatically or manually apply and maintain the standard 2 kPa pressure. The digital display resolution should reach 0.01 mm, and it should have a peak-hold or timed reading function to ensure measurement consistency.

Permeability testing instrument: Used to determine the vertical permeability coefficient and transmissivity. It mainly includes a constant head water supply system, a precision permeation clamping device, water volume measuring devices (such as measuring cylinders and electronic balances) and water level measuring rulers. The clamping device needs to ensure that the edge of the specimen is well sealed to prevent water flow short-circuiting.

Vibrating sieve machine and standard sieves: Used for determining the apparent opening size by the dry sieving method. The vibrating sieve machine should be able to provide a stable and repeatable vibration frequency and amplitude. It needs to be equipped with a complete set of standard test sieves and precisely graded standard granular materials (glass beads or standard sand), as well as an analytical balance with an accuracy of 0.01 g for particle weighing.

Xenon lamp aging test chamber: Used to simulate comprehensive climatic conditions such as outdoor ultraviolet light, temperature and humidity, for artificial accelerated aging tests. The equipment needs to be able to precisely control the irradiance, black panel temperature, chamber temperature and relative humidity, and follow the cycle conditions specified in the relevant standards (such as GB/T 16422.2).

Direct shear friction testing machine: Used to determine the interface friction characteristics between the geotextile and the soil or between geotextiles. The equipment includes upper and lower shear boxes, a normal loading system, a horizontal shear drive system and stress/displacement sensors. The lower shear box is filled with standard soil samples, and the upper shear box fixes the specimen. The friction coefficient and cohesion are obtained through shear tests.