ISO 12958-2:2020

Overview

ISO 12958-2:2020 specifies a performance test method to determine the constant-head in-plane water flow capacity of geotextiles and geotextile-related products. The standard defines how to measure volumetric flow per unit width under representative field-like conditions using project-specific boundary materials (for example soils), a range of normal compressive stresses, seating times and low hydraulic gradients. It is intended to assess short- to mid-term performance (including primary creep effects) and to evaluate how contact with soils or confinement affects the product’s transmissivity.

Key Topics and Requirements

• Test principle: measure steady-state flow within the plane of the geotextile at a constant head loss under defined stresses, gradient and boundary conditions.
• Apparatus: constant-head in-plane flow cell capable of maintaining precise head loss; minimum useful dimensions (cell width ≥ 0.2 m, effective flow length ≥ 0.3 m); discharge head ≤ 100 mm.
• Loading and control: loading mechanism must hold normal compressive stress with ≤1% or 1 kPa error; hydraulic head measurement requirements vary by gradient (pressure transducers required for gradients < 0.1).
• Boundary materials: soils or granular materials confined in thin membranes (membrane thickness ≤ 0.7 mm; tensile modulus ≤ 1.12 kN/m) to reproduce field contact without limiting intrusion.
• Water quality & conditions: temperature controlled between 18 °C and 22 °C (preferably near 20 °C); dissolved oxygen recommended ≤ 6 mg/kg to reduce air-clogging; filtered, de-aerated water for low flow rates.
• Performance metrics: outputs reported as performance in-plane water flow capacity q_perf(σ,i,t,b) in (l/s)/m at specified σ (kPa), hydraulic gradient i, seating time t, and boundary b. Leakage limits and blank-test leak checks are specified (leakage ≤ 5% of measured flow).
• Scope limitations: covers primary creep and direction-specific testing where relevant (e.g., geocomposites with discrete draining elements). It does not replace long-term durability, secondary/tertiary creep, chemical/biological clogging or installation effects.

Applications and Users

• Geotechnical and civil engineers designing drainage layers, retaining structures, landfill liners, and road subdrainage systems.
• Manufacturers and R&D labs validating geotextile and geocomposite drainage performance and transmissivity under realistic soil contact.
• Testing laboratories and quality control groups performing project-specific verification using actual site soils as boundary materials.
• Specifiers and contractors who need standardized performance data for selection and installation of drainage geosynthetics.

Practical uses include assessing geotextile intrusion into drainage cores, comparing directional flow capacity for asymmetric products, and verifying that a product meets project hydraulic performance under expected service loads.

Related Standards

• ISO 12958-1 (laboratory characterization; note results from Part 1 are not directly comparable)
• ISO 18325 (prefabricated vertical drains)
• ISO 9862, ISO 9863-1, ISO 10318-1 (sampling, thickness, terminology)
• ISO 2854, ISO 5813 (statistical and water quality methods)

Keywords: ISO 12958-2:2020, geotextiles, in-plane water flow, transmissivity, performance test, constant-head, hydraulic gradient, seating time, geocomposite.