ISO 11058 Geotextiles and Geotextile Related Products - Determination of Water Permeability Properties Perpendicular to the Plane Without Load

The ISO 11058 Geotextiles and geotextile-related products – Determination of perpendicular to plane water permeability properties without load, standard published by the International Organization for Standardization (ISO), describes two test methods for determining the perpendicular to plane water permeability properties of a single-layer geotextile or geotextile-related product:

• Constant pressure method
• Dropping pressure method

For the purposes of this standard, the velocity index expresses the velocity corresponding to a pressure drop of 50 mm across a sample and is expressed rounded to the nearest plus/minus 1 mm/s.

Test samples should not be folded during transport and should be transported as sparsely as possible to prevent damage to their structure. The sample should be held in a flat position without any load. Test samples should be taken in accordance with the ISO 9862 standard. Five test samples are cut from the product, each sized appropriately for the water permeability device to be used. If the results need to be determined within a specific confidence interval of the average, the number of test samples is determined according to the ISO 2854 standard. Samples should be clean, free of surface residues, and free from visible damage or folding marks.

In the constant pressure method, the principle is that a single unloaded geotextile or geotextile-related product layer is subjected to a unidirectional water flow perpendicular to the plane within a specific constant pressure range.

Falling pressure. The principle of this method is that a single unloaded geotextile or geotextile-related product layer is subjected to a unidirectional water flow perpendicular to the plane below the falling head.

In the world of geosynthetics and civil engineering, precise testing standards ensure that materials demonstrate reliable performance in real-world applications. One such critical standard is ISO 11058. This international standard provides a standardized method for measuring vertical water flow through geotextiles, a crucial feature for drainage, filtration, and separation functions in infrastructure projects.

The ISO 11058 standard includes a test method for determining the normal permeability (also known as permeability or water permeability coefficient) of geotextiles without external loading. Unlike in-plane permeability tests, this standard focuses on water flow perpendicular to the fabric plane, simulating conditions where geotextiles act as filters in soil retention systems, landfills, or road drains.

This standard, in its latest update, incorporates updates for improved accuracy, including better definitions of hydraulic pressure differences and sample conditioning. This standard also applies to all types of geotextiles, including woven, nonwoven and knitted, but excludes geomembranes or bituminous barriers.

The main objectives of this standard are:

• To provide reproducible results in laboratories worldwide.
• To provide design engineers with data for selecting geotextiles based on site-specific hydraulic requirements.
• To support quality control in production.

Geotextiles are porous fabrics used in civil engineering to separate, filter, reinforce, or drain soil. Their ability to allow water passage while retaining soil particles prevents clogging in applications such as:

• Road and railway embankments: Preventing pore pressure build-up.
• Waste storage areas: Facilitating the collection of leachate.
• Erosion control: In coastal or riverbank protection.

Low permeability can lead to system failures such as flooding or structural instability. The ISO 11058 standard measures this using the velocity index or permeability, calculated with the equations given within the standard. Typical values ​​for nonwoven geotextiles range from 0,01 to 2,0 s⁻¹, depending on fiber density and thickness.

This standard outlines the basic steps of constant pressure testing using specialized equipment. The main steps in this process are as follows:

• Sample preparation: Circular samples (typically 50-100 mm in diameter) are cut from the geotextile roll. They are kept at a temperature of 20 degrees plus/minus 2 degrees and 65 percent plus/minus 5 percent relative humidity for at least 24 hours. At least 5 samples are tested per sample collection.
• Device setup: A permeability cell with transparent walls is used for visual monitoring. Inlet/outlet connections for evacuated water, piezometers for pressure measurement, and a constant pressure tank are added.
• Test procedure: The sample is placed in the cell without compression. Hydraulic pressures (e.g., 1,0-100 mm) are applied to obtain gradients of 0,1-10. Once steady state is reached (usually after 1-5 minutes), the flow rate is measured. Air bubbles must be avoided, therefore deaerated water is used.
• Calculations and reporting: Permeability is calculated at multiple pressures to plot a characteristic curve. The average permeability, standard deviation, and any anomalies (e.g., turbulence at high flow rates) are reported.

The testing time is short (less than 30 minutes per sample), making it efficient for quality assurance.

Major projects worldwide rely on data compliant with the ISO 11058 standard. For example,

• High-speed rail in Europe: Geotextiles tested according to this standard provide drainage under the tracks.
• Mining waste dams: They are critically important in preventing liquefaction.
• Sustainable infrastructure: Helps in selecting environmentally friendly, recyclable geotextiles.

Some manufacturers are boosting global trade by having their products ISO 11058 certified. Non-compliance can lead to project delays or failures, as seen in some erosion control case studies. This has resulted in the permeability of soil pipes being underestimated.

The ISO 11058 standard measures unloaded permeability; for loaded conditions, the ISO 12958 standard applies. It does not evaluate long-term clogging, which is covered by the ISO 10722 (clogging index test) standard. For complete filtration design, the ISO 12956 standard is combined with pore size tests.

In conclusion, the ISO 11058 standard continues to be a cornerstone of geosynthetic testing in civil engineering, promoting safety and efficiency. As infrastructure demands increase, compliance with this standard is vital, especially in climate-resistant designs. Engineers and specifiers rely on this standard for implementation.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its customers, providing the advanced testing services they require, and assisting in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services to businesses in accordance with the "ISO 11058 Geotextiles and geotextile related products - Determination of permeability properties perpendicular to the plane without load" standard.