ISO/TS 18198:2023

TECHNICAL ISO/TS
SPECIFICATION 18198
First edition
2023-03
Determination of long-term flow of
geosynthetic drains
Reference number
© ISO 2023
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test equipment and procedures for determination of short-term in- plane water
flow . 1
4.1 Measurement of maximum hydraulic transmissivity and flow rate . 1
4.2 Test equipment . 2
4.2.1 Unidirectional flow . 2
4.2.2 Index and performance tests . . 5
4.3 Normal compressive loading and seating time . 5
4.4 Number of test specimens per sample per test . 6
4.5 Hydraulic gradient . 7
5 Determination of long-term flow performance . 7
5.1 General . 7
5.2 Reduction factors (R ) . 8
F
5.3 Reduction factor for intrusion (R and R ) . 9
F,in F,GI
5.4 Reduction factor for creep (R ) . 10
F,cr
5.4.1 General . 10
5.4.2 Time-temperature superposition methods . 11
5.5 Reduction factors for chemical clogging (R ) and biological clogging (R ) .12
F,CC F,BC
5.6 Additional considerations . 13
5.6.1 Design life .13
5.6.2 Design temperature .13
5.6.3 Installation damage . 14
5.6.4 Durability of the polymers . 14
6 Alternative procedures to determine Q .14
a
6.1 General . 14
6.2 Long-term reduction of water flow capacity due to compressive creep by the BAM
(Germany) method . 14
6.3 Thickness-dependent short-term flow testing using SIM . 17
6.4 Time dependent loading followed by flow capacity measurements . 19
Bibliography .20
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 221, Geosynthetics.
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
Introduction
The most commonly used drainage geosynthetics are the geocomposites which are produced by
laminating one or two geotextiles, with a filter function, onto a drainage core. Examples are included in
Figure 1.
a) Geonet core b) Geomat core c) Cuspated core d) Perforated tube core
Figure 1 — Examples of drainage cores
The components generally have the following characteristics under operating conditions:
— filtering component:
— adequate permeability to gases and liquids in the direction perpendicular to the filter plane;
— retention capacity of the soil particles;
— drainage core:
— adequate permeability to gases and liquids in the direction planar to the drainage structure;
— adequate compressive strength and creep resistance for the loads to be applied.
The geocomposites are often defined by the drainage cores: geomats (GMA), geonets (GNT), geospacers
(GSP), multi-linear drains.
v
TECHNICAL SPECIFICATION ISO/TS 18198:2023(E)
Determination of long-term flow of geosynthetic drains
1 Scope
This document specifies methods of deriving reduction factors for geosynthetic drainage materials to
account for intrusion of filter geotextiles, compression creep, and chemical and biological degradation.
It is intended to provide a link between the test data and the codes for design with geosynthetic drains.
The geosynthetics covered include those whose primary purpose is planar drainage, such as geonets,
cuspated cores only, or cuspated cores combined with laminated filter geotextiles, and drainage liners,
where the drainage core is made from polypropylene and high-density polyethylene. The majority
of geosynthetic drains are geocomposites with geotextiles laminated to a drainage core and it is
important, where possible, to consider the drainage behaviour of the geocomposite as a whole rather
than the behaviour of the component parts in isolation.
This document does not cover the strength of overlaps or joints between geosynthetic drains nor
whether these might be more or less durable than the basic material. It does not apply to geomembranes,
for example, in landfills. It does not cover the effects of dynamic loading nor any change in mechanical
properties due to soil temperatures below 0 °C, or the effects of frozen soil. This document does not
cover uncertainty in the design of the drainage structures, nor the human or economic consequences of
failure. Design guidance for geosynthetic drains is found in ISO/TR 18228-4.
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 10318-1, Geosynthetics — Part 1: Terms and definitions
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 10318-1 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Test equipment and procedures for determination of short-term in- plane
water flow
4.1 Measurement of maximum hydraulic transmissivity and flow rate
The primary function of geosynthetic drains is to convey or transmit fluid within the flow direction(s)
of a drainage layer. The discharge capacity can be given in terms of:
— Specific flow rate, which is the discharge per unit width in the geosynthetic drain, under a specified
hydraulic gradient, as per Formula (1):
Qq= / B (1)
Some users of flow tests desire to index the discharge rate per unit width to the applied hydraulic
energy or hydraulic gradient at which flow is measured. In this case:
— Hydraulic transmissivity, which is the discharge per unit width of the geocomposite and per unit of
hydraulic gradient, as per Formula (2):
θ =()qB / /i (2)
The concepts of transmissivity and flow capacity were developed specifically to avoid consideration
of the thickness as it is often difficult to specifically define the thickness of a geosynthetic drain in
application.
Transmissivity is equal to flow rate only at a gradient of 1. Note also that the numerical value of
transmissivity can be very different than the numerical value of the specific flow rate at small hydraulic
gradients (e.g. at i = 0,1 transmissivity is 10 times the specific flow rate).
The discharge capacity test for a geosynthetic drain is performed in accordance with ISO 12958-1,
ISO 12958-2 or ASTM D4716.
4.2 Test equipment
4.2.1 Unidirectional flow
The apparatus for these test methods are relatively simplistic in their design and ability to measure a
discharge capacity or flow rate per unit width or transmissivity (Figure 2). By maintaining a constant
head during the test, at a given normal stress, boundary conditions, and seating time, the flow rate Q of
the geosynthetic drain can be determined using Formula (3):
q
Q =⋅ R (3)
σ ,,it ,bT
B
Where
Q is the numerical value of the in-plane water flow capacity per unit width at a defined stress
σ,i,t,b
σ, gradient i, seating time under load prior to flow measurement t and boundary con
...