In major projects such as water conservancy, highways, railways, and environmental protection, geotextiles serve as “invisible guardians.” Their core functions—separation, filtration, reinforcement, and drainage—directly determine soil structural stability and long-term engineering safety. Whether for dam seepage control, roadbed reinforcement, slope protection, or underground drainage, the performance of geotextiles is critical. Precise and comprehensive testing is the core process to ensure they perform optimally and mitigate project risks.

I. Functions of Geotextiles

Geotextiles are permeable geosynthetic materials made from synthetic fibers through processes like needle-punching or weaving. They are categorized into woven, nonwoven, and composite geotextiles, with their functions directly addressing core engineering needs:

1. Filtration and Counter-filtration

Filtration is one of geotextiles' primary missions. When water permeates from fine-grained to coarse-grained soil layers, geotextiles act as “intelligent screens,” allowing water to pass while firmly retaining fine soil particles. This prevents soil erosion-induced hazards like piping and soil flow. The reverse filtration function prevents the loss of fill material within drainage structures during reverse water flow, maintaining the integrity of surrounding soil. This capability is particularly critical in plastic blind drains and dam drainage systems. Substandard filtration performance not only clogs drainage channels but also disrupts soil structure, ultimately causing project settlement and collapse.

2. Reinforcement and Separation

In roadbeds, slopes, and similar projects, geotextiles enhance soil tensile strength and deformation resistance through reinforcement, dispersing concentrated stresses to prevent soil failure under external forces. Simultaneously, their separation function segregates construction materials with differing physical properties (particle size, density, consistency), preventing mixing of soil with aggregates, concrete, etc. This maintains the overall structural integrity and load-bearing capacity of materials, laying the foundation for project stability. Additionally, geotextiles provide auxiliary functions such as protection, drainage, and puncture resistance, forming a comprehensive engineering protection system.

II. Key Test Items

The performance of geotextiles must be validated through multidimensional testing covering four major categories: physical properties, mechanical properties, hydraulic properties, and durability. Each test directly corresponds to the material's ability to ensure soil stability and filtration efficiency.

1. Physical Properties Testing

Physical properties form the foundation for geotextile functionality. Core tests include:

1.1Basis Weight: Determined by weighing (per GB/T 13762 standard), this metric directly relates to geotextile thickness, strength, and cost control. Deviations must be within ±8% (slight variations exist for different specifications). Insufficient basis weight compromises strength, while excess may impair permeability.

1.2Thickness Measurement: Measured using a geotextile thickness gauge under specified pressure (GB/T 13761 standard). Thickness directly impacts porosity and drainage capacity. For example, 100g/m² short-fiber geotextile must be no less than 0.9mm thick, while 600g/m² specifications require a minimum thickness of 4.1mm.

1.3Visual Quality: Visually inspect for surface uniformity, creases, tears, impurities, or other defects. Any cosmetic flaw may become a stress concentration point, compromising tear resistance and puncture resistance during use.

2. Mechanical Property Testing

Mechanical properties determine geotextile reinforcement and protection effectiveness, serving as the key defense against external damage. Core test items include:

2.1Tensile Strength and Elongation at Break: Conducted via wide-strip tensile testing (GB/T 15788) using a universal testing machine to determine maximum longitudinal/transverse tensile stress and strain rates. This ensures sufficient strength and elongation in both dry and wet conditions. For example, 200g/m² short-fiber geotextile must exhibit a longitudinal breaking strength of no less than 6.5kN/m.

2.2Tear Strength and Puncture Resistance: Tear strength is tested using the trapezoidal tear method per GB/T 13763, while puncture resistance is evaluated via the CBR puncture test (GB/T 14800). These assess the geotextile's ability to withstand punctures and tears during construction and use, preventing catastrophic failure from localized damage.

2.3 Abrasion Resistance: Tested using the sandpaper/slider method (GB/T 17636) to simulate friction with soil and gravel in engineering applications. This ensures long-term durability against abrasive wear, particularly suitable for high-friction environments like roadbeds and slopes.

3. Hydraulic Performance Testing

Hydraulic properties directly determine filtration efficiency and drainage effectiveness, constituting the core verification for geotextile functionality:

3.1Vertical Permeability Coefficient: Measured using a geosynthetic vertical permeability tester (per GB/T 17633 standard) to assess water flow penetration through the fabric. Values must be controlled between 1.0×10⁻¹⁰ and 9.9×10⁻¹⁰ cm/s to ensure smooth water passage 3.2Effective Pore Size: Determined using dry or wet sieving methods (GB/T 14799), with the core metric being O₉₅ (95% of pores smaller than this value). Typically controlled between 0.07–0.2 mm, this size retains fine soil particles without causing blockage due to excessive smallness, achieving a balance between “soil retention and drainage.”

4. Durability Testing

Engineering applications often span decades, requiring geotextiles to withstand complex environmental erosion. Core testing includes:

4.1Aging Resistance and Corrosion Resistance: Simulating UV exposure and temperature fluctuations via high-temperature aging chambers (GB/T 17631), and verifying stability in acidic/alkaline soils and water bodies using acid-alkali resistance testers (GB/T 17632). This ensures tensile strength retention meets project requirements—e.g., maintaining specified longitudinal and transverse strength retention after 3 days immersion in 0.025 mol/L sulfuric acid or saturated calcium hydroxide solution.

4.2Microbial Resistance: Tests resistance to microorganisms and insect damage to prevent degradation in humid soil environments and maintain performance stability.

III. Testing Standards and Instruments

Precise testing relies on a comprehensive standard system and professional instruments, both of which collectively ensure the authority, accuracy, and comparability of test results.

1. Core Testing Standards

China has established a comprehensive testing standard system for geotextiles, covering both product standards and method standards. The core standards include:

1.1 Product Standards: “Short Fiber Needle-punched Nonwoven Geotextile” (GB/T 17638-2017), “Filament Spunbonded Needle-punched Nonwoven Geotextile” (GB/T 17639-2008), “Composite Geomembrane” (GB/T 17642-2018), etc., specifying performance requirements for different types of geotextiles.

1.2Method Standards: Tensile Testing (GB/T 15788), Tear Testing (GB/T 13763), Permeability Coefficient Determination (GB/T 17633), etc., standardizing testing procedures and operational details.

1.3 Industry Specifications: Specialized specifications for sectors like highway engineering (JT/T 520-2017) and construction engineering, defining sampling rules and project-specific requirements.

2. The Critical Role of Professional Testing Instruments

Textile testing instruments serve as core tools for achieving precise measurements. Tailored to the characteristics of geotextiles, a series of specialized equipment is required:

2.1 Mechanical Performance Testing Instruments: Universal testing machines and computer-controlled electronic universal testing machines for tensile, tear, and puncture strength tests, ensuring accurate and traceable data.

2.2 Hydraulic performance testing instruments: Vertical permeameters and effective pore size analyzers for precise control of flow parameters, determining permeability coefficients and pore size distributions.

2.3 Physical and durability testing instruments: Automatic geotextile mass per unit area/thickness detection systems, high-temperature aging chambers, and acid-alkali resistance testers enable efficient batch testing and environmental simulation.

Professional testing instruments not only meet standard requirements but also provide intelligent data analysis. This delivers precise guidance for project selection and quality control, mitigating engineering risks caused by testing deviations.

IV. Conclusion

As the “invisible guardian” of engineering construction, geotextiles rely on comprehensive, high-standard testing and inspection to ensure soil stability and filtration efficiency. From fundamental control of physical properties to precise verification of mechanical and hydraulic performance, and long-term assessment of durability, each test bears the critical responsibility of engineering safety. Looking ahead, as engineering demands for geotextile performance continue to rise, testing technologies and instruments will undergo continuous iteration and advancement. Only by adhering to the fundamental principles of scientific testing can geotextiles fully realize their potential, safeguarding the long-term stability and operation of major engineering projects.

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