EN ISO 12956:2020

• Abstract:

  This document specifies a method for the determination of the characteristic size of the openings of a single layer of a geotextile or geotextile-related product using the wet-sieving principle.

• Status: Published
• Publication Date: 14-Jan-2020
• Withdrawal Date: 30-Jul-2020
• ICS: 59.080.70 - Geotextiles
• Technical Committee: CEN/TC 189 - Geotextiles and geotextile-related products
• Drafting Committee: CEN/TC 189/WG 4 - Hydraulic testing
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 15-Jan-2020
• Completion Date: 15-Jan-2020
• Directive: Harmonized Standard305/2011 - Regulation (eu) No 305/2011 of the European Parliament and of the Council of 9 march 2011 laying down harmonised conditions for the marketing of construction products and repealing council directive 89/106/eec
• Mandate: M/107 - Mandate to CEN/CENELEC concerning the execution of standardization work for harmonized standards on geotextiles
• Ref Project: SIST EN ISO 12956:2020 - Geotextiles and geotextile-related products - Determination of the characteristic opening size (ISO 12956:2019)

• Replaces: EN ISO 12956:2010 - Geotextiles and geotextile-related products - Determination of the characteristic opening size (ISO 12956:2010)
• Effective Date: 11-Mar-2015
• Refers: ISO 9862:2005 - Geosynthetics — Sampling and preparation of test specimens
• Effective Date: 25-Aug-2026
• Refers: ISO 10320:2019 - Geosynthetics — Identification on site
• Effective Date: 25-Aug-2026
• Refers: EN 1744-1:2009/FprA1 - Tests for chemical properties of aggregates - Part 1: Chemical analysis
• Effective Date: 28-Jan-2026
• Refers: EN ISO 16546:2020 - Thermal insulating products for building applications - Determination of freeze-thaw resistance (ISO 16546:2020)
• Effective Date: 28-Jan-2026
• Referred By: EN 13265:2000 - Geotextiles and geotextile-related products - Characteristics required for use in liquid waste containment projects
• Effective Date: 28-Jan-2026
• Referred By: EN 13257:2016 - Geotextiles and geotextile-related products - Characteristics required for use in solid waste disposals
• Effective Date: 28-Jan-2026
• Referred By: EN 13255:2014 - Geotextiles and geotextile-related products - Characteristics required for use in the construction of canals
• Effective Date: 28-Jan-2026
• Referred By: EN 13249:2014+A1:2015 - Geotextiles and geotextile-related products - Characteristics required for use in the construction of roads and other trafficked areas (excluding railways and asphalt inclusion)
• Effective Date: 28-Jan-2026
• Referred By: EN 13249:2014 - Geotextiles and geotextile-related products - Characteristics required for use in the construction of roads and other trafficked areas (excluding railways and asphalt inclusion)
• Effective Date: 28-Jan-2026
• Referred By: EN 13251:2014+A1:2015 - Geotextiles and geotextile-related products - Characteristics required for use in earthworks, foundations and retaining structures
• Effective Date: 28-Jan-2026
• Referred By: EN 13254:2014 - Geotextiles and geotextile-related products - Characteristics required for use in the construction of reservoirs and dams
• Effective Date: 28-Jan-2026
• Referred By: EN 13250:2000 - Geotextiles and geotextile-related products - Characteristics required for use in the construction of railways
• Effective Date: 28-Jan-2026
• Referred By: EN 13252:2014 - Geotextiles and geotextile-related products - Characteristics required for use in drainage systems
• Effective Date: 28-Jan-2026
• Referred By: EN 13255:2014+A1:2015 - Geotextiles and geotextile-related products - Characteristics required for use in the construction of canals
• Effective Date: 28-Jan-2026

Overview

EN ISO 12956:2020 (identical to ISO 12956:2019) specifies a laboratory wet‑sieving test method to determine the characteristic opening size of a single layer of geotextiles and geotextile‑related products. The characteristic opening size (commonly noted as O90) is defined by the particle size of a granular test material that passes through the geotextile such that 90% of the passing mass is finer than that particle size. This standard supersedes EN ISO 12956:2010 and is published by CEN/ISO for geosynthetics testing.

Key topics and technical requirements

• Test principle: wet sieving of granular material through a clamped geotextile specimen; O90 is derived from the passing granular particle size distribution.
• Apparatus essentials:
  • Sieving unit with vertical motion at 50–60 Hz and 1.5 mm amplitude (3 mm swing height); minimum exposed sieving diameter 130 mm.
  • Water supply and spray nozzle(s) enclosed to prevent material loss; recommended flow approx. 0.5 L/min at ~300 kPa with a flow regulator.
  • Support grid (mesh 10 ± 1 mm, wire 1–2.5 mm) to avoid specimen deformation and a sealed cover to prevent leakage.
  • Filter paper (max opening 10 µm), balance with max error 0.03 g, and oven up to 110 °C.
• Granular material: cohesion‑less, essentially round particles (e.g., glass beads) with controlled gradation and a coefficient of uniformity Cu between 3 and 20; Annex B provides guidance and optimisation curves for selecting gradation to improve accuracy.
• Specimens: cut five test specimens per sample; handle flat and avoid folding; specimen selection and preparation per ISO 9862.
• Documentation: test procedure, calculations, and reporting requirements are specified (including annexes for mesh sizes, worked example, and knitted tubular preparation).

Applications and users

• Practical uses: selection and quality control of geotextiles for filtration, drainage, separation and erosion control, where pore/opening size influences soil retention and hydraulic performance.
• Typical users: geotechnical and civil engineers, geosynthetic manufacturers, independent testing laboratories, specifications writers, and contractors involved in drainage and earthworks projects.

Related standards

• ISO 9862 - Sampling and preparation of test specimens (normative reference)
• ISO 10320 - Identification on site (normative reference)
• EN ISO 12956:2020 replaces the 2010 edition; consult annexes (A–C) for mesh sizes, examples, and preparation guidance.

Keywords: EN ISO 12956:2020, ISO 12956:2019, geotextiles, characteristic opening size, O90, wet‑sieving, geosynthetics, filtration test, test method.

SLOVENSKI STANDARD
01-marec-2020
Nadomešča:
SIST EN ISO 12956:2012
Geotekstilije in geotekstilijam sorodni izdelki - Ugotavljanje značilnih velikosti
odprtin (ISO 12956:2019)
Geotextiles and geotextile-related products - Determination of the characteristic opening
size (ISO 12956:2019)
Geotextilien und geotextilverwandte Produkte - Bestimmung der charakteristischen
Öffnungsweite (ISO 12956:2019)
Géotextiles et produits apparentés - Détermination de l'ouverture de filtration
caractéristique (ISO 12956:2019)
Ta slovenski standard je istoveten z: EN ISO 12956:2020
ICS:
59.080.70 Geotekstilije Geotextiles
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 12956
EUROPEAN STANDARD
NORME EUROPÉENNE
January 2020
EUROPÄISCHE NORM
ICS 59.080.70 Supersedes EN ISO 12956:2010
English Version
Geotextiles and geotextile-related products -
Determination of the characteristic opening size (ISO
12956:2019)
Géotextiles et produits apparentés - Détermination de Geotextilien und geotextilverwandte Produkte -
l'ouverture de filtration caractéristique (ISO Bestimmung der charakteristischen Öffnungsweite
12956:2019) (ISO 12956:2019)
This European Standard was approved by CEN on 5 December 2019.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 12956:2020 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 12956:2020) has been prepared by Technical Committee ISO/TC 221
"Geosynthetics" in collaboration with Technical Committee CEN/TC 189 “Geosynthetics” the secretariat
of which is held by NBN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by July 2020, and conflicting national standards shall be
withdrawn at the latest by July 2020.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 12956:2010.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 12956:2019 has been approved by CEN as EN ISO 12956:2020 without any modification.

INTERNATIONAL ISO
STANDARD 12956
Third edition
2019-12
Geotextiles and geotextile-related
products — Determination of the
characteristic opening size
Géotextiles et produits apparentés — Détermination de l'ouverture de
filtration caractéristique
Reference number
ISO 12956:2019(E)
©
ISO 2019
ISO 12956:2019(E)
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

ISO 12956:2019(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Apparatus and materials. 2
6 Test specimens. 5
6.1 Handling. 5
6.2 Selection. 5
6.3 Number and dimensions . 5
6.4 Specimen condition . 6
7 Procedure. 6
8 Calculation and expression of results . 8
9 Test report . 8
Annex A (normative) Mesh sizes .10
Annex B (informative) Example of the determination of the characteristic opening size .11
Annex C (informative) Preparation of knitted tubular geotextiles for testing .13
Bibliography .15
ISO 12956:2019(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 221, Geosynthetics.
This third edition cancels and replaces the second edition (ISO 12956:2010), which has been technically
revised. The main changes compared to the previous edition are as follows:
— the average used in order to select the number of specimens is modified (25 % to 15 %);
— explanations are given for the preparation of knitted tubular geotextiles.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2019 – All rights reserved

INTERNATIONAL STANDARD ISO 12956:2019(E)
Geotextiles and geotextile-related products —
Determination of the characteristic opening size
IMPORTANT — The electronic file of this document contains colours which are considered to be
useful for the correct understanding of the document. Users should therefore consider printing
this document using a colour printer.
1 Scope
This document specifies a method for the determination of the characteristic size of the openings of a
single layer of a geotextile or geotextile-related product using the wet-sieving principle.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 9862, Geosynthetics — Sampling and preparation of test specimens
ISO 10320, Geosynthetics — Identification on site
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
d
n
particle size for which n % mass fraction is smaller than the mass of measured particles
3.2
O
size of opening which is equal to the particle of size d of the granular material which passes through
the geotextile or geotextile-related product, expressed in µm
3.3
C
u
coefficient of uniformity, defined as d /d
60 10
4 Principle
The principle of the test is to determine the opening size (O ) which corresponds to the specified size
of the granular material passed.
ISO 12956:2019(E)
5 Apparatus and materials
5.1 Sieving apparatus, composed of the following elements.
5.1.1 Sieving unit, allowing for the testing of a specimen with an exposed sieving area corresponding
to a minimum diameter of 130 mm, complying with the following requirements:
a) sieving device, with a frequency of 50 Hz to 60 Hz;
b) predominantly vertical sieve motion capable of maintaining a 1,5 mm amplitude (3 mm swing
height, see Figure 1) over the period of test.
Key
a
X time 1,5 mm amplitude.
b
Y swing height 3 mm swing height.
Figure 1 — Amplitude and swing height
5.1.2 Water supply system.
5.1.3 Spray nozzle(s), to ensure even wetting of the test specimen, enclosed in a transparent cylinder
and/or covering cap to avoid soil or granular material loss.
It is recommended that the nozzle(s) be capable of a water discharge of approximately 0,5 l/min at a
working pressure of about 300 kPa. A valve should be available to regulate the flow of water.
5.1.4 Specimen clamping device, to transmit all the energy to the specimen during sieving.
5.1.5 Pan, affixed to the sieving apparatus, with a connection tube to the device for filtering the water
and collecting granular material passing through the specimen.
NOTE Typical sieving equipment is represented in Figure 2.
2 © ISO 2019 – All rights reserved

ISO 12956:2019(E)
Key
1 water supply 7 pan
2 spray nozzle(s) 8 connection tube
3 specimen clamping device 9 amplitude regulator
4 granular material 10 filter paper
5 specimen 11 collection device
6 support grid
Figure 2 — Example of sieving apparatus
5.1.6 Grid, with wire between 1 mm and 2,5 mm in diameter and a mesh size of (10 ± 1) mm, with a
minimum of 90 % opening area to support the specimen during the test, to avoid excessive deformation
of the specimen under the weight of the granular material.
5.1.7 Sealant, in order to avoid loss of granular material.
NOTE Examples of sealant positions are represented in Figure 3.
ISO 12956:2019(E)
a) Example with two rubber rings b) Example with one rubber ring
Key
1 cover
2 PVC or metallic ring
3 rubber ring
4 specimen
5 support grid
Figure 3 — Examples of sealant positions
5.1.8 Cover, fully transparent or equipped with a transparent window to permit observation and
check that there is no w
...