ISO 12958-1:2020

INTERNATIONAL ISO
STANDARD 12958-1
First edition
2020-10
Geotextiles and geotextile-related
products — Determination of water
flow capacity in their plane —
Part 1:
Index test
Géotextiles et produits apparentés — Détermination de la capacité de
débit dans leur plan —
Partie 1: Essai index
Reference number
©
ISO 2020
© ISO 2020
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Published in Switzerland
ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus and materials. 2
6 Specimens . 6
6.1 Handling. 6
6.2 Selection. 6
6.3 Number and dimensions . 6
6.4 Specimen condition . 7
7 Test procedure . 7
8 Calculations and expression of results . 8
8.1 Products with a continuous structure (i.e. with no discrete draining elements) . 8
8.2 Products with discrete draining elements . 8
8.3 Graphical representation . 9
9 Test report .10
Annex A (informative) Determination of the correction factor R for conversion to a water
T
temperature of 20 °C .11
Annex B (informative) Experimental data and calculations for a specimen .13
Bibliography .14
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
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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
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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.
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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, in collaboration with
the European Committee for Standardization (CEN) Technical Committee CEN/TC 189, Geosynthetics,
in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This first edition of ISO 12958-1, together with ISO 12958-2, cancels and replaces ISO 12958:2010,
which has been technically revised.
The main changes to ISO 12958:2010 are as follows:
— introduction of the concept of index versus performance test;
— permission given to test using rigid/rigid, soft/soft or soft/rigid boundaries;
— addition of guidance for testing cuspated sheets on a single side and for testing multilinear drainage
geocomposites;
— withdrawal of apparatus types b) and c);
— several cosmetic improvements, in particular terms and definitions, procedure, calculation and
reporting.
A list of all parts in the ISO 12958 series can be found on the ISO website.
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 2020 – All rights reserved

INTERNATIONAL STANDARD ISO 12958-1:2020(E)
Geotextiles and geotextile-related products —
Determination of water flow capacity in their plane —
Part 1:
Index test
1 Scope
This document specifies a method for determining the constant-head water flow capacity within the
plane of a geotextile or geotextile-related product. This document describes the in-plane water flow
index test, only applicable to factory-assembled products. For the in-plane water flow performance test,
see ISO 12958-2.
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 2854, Statistical interpretation of data — Techniques of estimation and tests relating to means and
variances
ISO 5813, Water quality — Determination of dissolved oxygen — Iodometric method
ISO 9862, Geosynthetics — Sampling and preparation of test specimens
ISO 9863-1, Geosynthetics — Determination of thickness at specified pressures — Part 1: Single layers
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
normal compressive stress
σ
compressive stress normal to the plane of the geotextile or geotextile-related product, expressed in
kilopascals [kPa]
3.2
in-plane flow
Q
fluid flow within the geotextile or geotextile-related product and parallel to its plane, expressed in
litres per second [l/s]
3.3
in-plane water flow capacity
q
p index(σ/i)
volumetric flow rate of water per unit width of specimen at a defined normal compressive stress (σ),
hydraulic gradient (i), measured in the present index test and expressed in litres per second per meter
[(l/s)/m]
Note 1 to entry: The term 'transmissivity' is related to laminar flow conditions only and equals the water flow
capacity at a hydraulic gradient equal to unity. As non-laminar flow may occur, the term 'water flow capacity' is
preferred.
3.4
hydraulic gradient
i
ratio of the head loss in the geotextile or geotextile-related product specimen to the distance between
two measuring points within the geotextile or geotextile-related product
1)
Note 1 to entry: ISO/TR 18228-4 provides information on the significance of the hydraulic gradient.
3.5
contact surface
surface contacting the specimen
Note 1 to entry: Contact surfaces may be either closed-cell foam rubber on both sides (F/F), smooth rigid
membrane on one side and closed-cell foam rubber on the other side (R/F) or smooth rigid membrane on both
sides (R/R).
3.6
in-plane water flow index test
test that yields an indication of the in-plane water flow
3.7
in-plane water flow performance test
test to confirm full compliance of the in-plane water flow with the requirements under specified
conditions
4 Principle
The flow of water within the plane of a geotextile or geotextile-related product is measured under
varying normal compressive stresses, with typical hydraulic gradients and with defined contact
surfaces.
5 Apparatus and materials
5.1 Constant-head in-plane water flow apparatus, as follows:
a) The apparatus shall be capable of maintaining a constant head loss at different water levels, at least
those corresponding to hydraulic gradients of 0,1 and 1,0, while maintaining a water head at the
point of discharge not greater than 100 mm.
b) If the average water head above the specimen exceeds 100 mm, and the applied normal load is
equal to or less than 20 kPa, the normal stress shall be corrected for the excess considering the
average water head.
c) The apparatus shall be capable of maintaining the proposed normal compressive stress on the
specimen without any deformation which would influence the test results.
1) Under preparation. Stage at the time of publication: ISO/CD TR 18228-4:2020.
2 © ISO 2020 – All rights reserved

d) The apparatus shall include a loading mechanism capable of exerting a constant normal compressive
stress on the geotextile or geotextile-related product specimen to a maximum permissible error
of ± 5 % of applied normal compressive stress.
e) The surfaces contacting the specimen should be either:
— foam rubber (F) whose properties should satisfy the compression deflection envelope,
illustrated in Figure 1, when tested in accordance with ISO 9863-1; or
— smooth rigid (R) high-density polyethylene liner 2 mm thick without any surface damage.
Performances of a geotextile-related product with any other boundary condition can be measured
in accordance with the performance test of ISO 12958-2.
f) For specimens with a thickness up to 10 mm, foam rubber with a nominal thickness of 10 mm shall
be used on each face.
g) For specimens with a thickness between 10 mm and 25 mm, foam rubber with a nominal thickness
of 1 to 1,25 times the specimen thickness shall be used on each face.
h) For specimens with a thickness over 25 mm, the foam rubber on each face shall have a nominal
thickness of 25 mm.
i) Two layers of foam rubber may be combined to achieve the desired thickness only when the foam
thickness is greater than 10 mm.
j) The width of the foam shall be the same as that of the loading platen. The length of the foam should
normally be the same as the loading platen. However, to avoid obstruction at both the inlet and
outlet due to compression of the foam, it is recommended that the length of the foam be reduced,
where necessary, by 0,4 times its nominal thickness.
k) The test report shall include the specific boundary used.
l) The multiple use of foam rubber should be carefully monitored. The foam rubber shall be discarded
if there is more than 10 % deformation in thickness tested in accordance with ISO 9863-1 at 2 kPa.
m) The apparatus shall have a minimum width of 0,2 m and a minimum net hydraul
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