ISO/TR 18228-6:2023

TECHNICAL ISO/TR
REPORT 18228-6
First edition
2023-12
Design using geosynthetics —
Part 6:
Protection
Conception utilisant des géosynthétiques —
Partie 6: Protection
Reference number
© ISO 2023
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions . 1
3.2 Symbols . . 1
4 Concepts and fundamental principles . 1
5 Design approaches for protection . 3
6 Laboratory testing for protection . 6
6.1 General . 6
6.2 Index testing . 6
6.2.1 Burst strength and elongation (ISO 12236). 6
6.2.2 Tear strength (ISO 9073-4) . 6
6.2.3 Mass (ISO 9864) and thickness (ISO 9863-1) . 6
6.2.4 Needle free . 6
6.3 Field testing . 6
6.4 Performance-index testing . 7
6.4.1 General . 7
6.4.2 Undertaking and reporting of the cylinder test . 7
7 Handling and installation .11
8 Identification .12
Bibliography .13
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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different types of ISO document should be noted. This document was drafted in accordance with the
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 221, Geosynthetics, Working group WG 6,
Design using geosynthetics.
A list of all parts in the ISO/TR 18228 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
Introduction
The ISO/TR 18228 series provides guidance for designs using geosynthetics for soils and below ground
structures in contact with natural soils, fills and asphalt. The series contains 10 parts which cover
designs using geosynthetics, including guidance for characterisation of the materials to be used and
other factors affecting the design and performance of the systems which are particular to each part,
with ISO/TR 18228-1 providing general guidance relevant to the subsequent parts of the series.
The series is generally written in a limit state format and guidelines are provided in terms of partial
material factors and load factors for various applications and design lives, where appropriate.
This document includes information relating to the use of geosynthetics in a protective function.
v
TECHNICAL REPORT ISO/TR 18228-6:2023(E)
Design using geosynthetics —
Part 6:
Protection
1 Scope
This document provides general considerations to support design guidance for the evaluation of
geosynthetics to fulfil a protective function to any surface or material placed in contact with the
protective element.
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
ISO 10318-2, Geosynthetics — Part 2: Symbols and pictograms
3 Terms, definitions and symbols
3.1 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/
3.2 Symbols
For the purposes of this document, the symbols in ISO 10318-2 apply.
4 Concepts and fundamental principles
Geosynthetics for protection (protectors) are frequently incorporated with other geosynthetics and soil
components in barrier systems. The objective of any barrier protector is to ensure that the stresses and
strains encountered during the construction phase and operational life of a site pose no significant risk
of damage to the barrier. The aim of the geosynthetic protection layer is to limit damage to the barrier
caused by the drainage aggregate placed above the barrier (see Figure 1 and Figure 2). Designers would
normally assess the potential for stresses and strains in the protector. This document covers the use of
geosynthetics as a protection layer for barriers.
Figure 1 — Drainage aggregate in contact with protection geotextile
Figure 2 — Placement of drainage aggregate
The purpose of the protective layer is to:
— minimize the risk of barrier damage or puncture during construction i.e. placement of the aggregate
drainage layer (dynamic loads) (static loads). The test methods described in Clause 4 don’t cover this
aspect of the design. Test pads using the actual geotextile grade, drainage aggregate and placement
equipment are normally performed in order to assess the minimum aggregate placement thickness.
Figure 3 shows barrier damage from a rounded river gravel due to trafficking with <150 mm cover;
and
— minimize the localized strains in the barrier during the subsequent operation and life of the
containment facility. Hence reducing the risk for future mechanical damage forming due to, for
example, environmental stress cracking.
Figure 3 — Barrier damage due to construction traffic
Figure 4 — Deformation without protection layer
Figure 5 — Deformation with protection layer
A geosynthetic can provide some stress reduction (Figures 4 and 5) however, this layer alone would not
normally be relied upon to reduce all stresses from the barrier. While strain minimization is desirable,
designers would normally be aware that zero strain is unlikely to be achieved.
5 Design approaches for protection
Table 1 outlines some of the common issues designers normally consider in selecting the most effective
geosynthetic for protection.
Table 1 — Issues considered by designers
Environment Issue
— The likely stresses and strains imposed during the
construction period.
— The likely stresses and strains imposed by
settlement and movement.
— The likely stresses and strains imposed by the
materials placed in contact with the geosynthetic,
particularly any drainage stone.
Physical
— The duration of exposure to ultraviolet light.
— The likely temperatures expected adjacent to the
geosynthetic and whether these are likely to have
a damaging effect upon the material properties in
any way.
— The interface friction angles between the materials
around the geosynthetics and the geosynthetics
themselves, particularly on slopes.
— The likely interaction between the geosynthetic
and the material around the geosynthetic. It is
usual for there to be little or no interaction.
— The polymeric structure of the geosynthetic itself
and whether it will be prone to degradation which
Chemical would affect its ability to protect the barrier. The
polymeric structure would normally be such as
to cover the predicted life of the geosynthetic and
barrier.
— The effects of mineral precipitation on the
geosynthetics performance.
— The effects of microbial growth on the polymer of
the geosynthetic.
Biological
— The effects of microbial growth on the
characteristics of the geosynthetic.
Currently there are two main approaches regarding the design of protective geosynthetics: strain
minimization and resistance to puncture.
Strain minimization considers whether the protective effect of a protection layer is sufficient if the load
distribution is dispersed to such an extent that only slight indentations arise in the barrier. By limiting
the strain of a barrier to within a strain limit, damage can usually be prevented in the microstructure
of the material that would otherwise develop when strains exceed this limit. Excessive strain can
sometimes develop into macroscopic stress cracks. Conversely, stress crack formation is impossible
when deformations stay below this limiting strain, regardless of the stresses imposed.
[1]
A limiting value for the permissible deformation can be derived another way. Koch et al. suggested
that tensile stresses be considered. These arise from different deformation events, taking stress
relaxation in the barrier into account. The stresses are then compared with the stress level that the
HDPE material can tolerate over the long-term without stress crack formation (long-term pipe pressure
tests).
[2]
Narejo defined levels of protection against puncture for barriers under typical loading conditions as
follows:
— Level I: typically applied to barrier systems for hazardous waste facilities. This level requires that
the barrier system be designed such that less than 0,25 % localized strain (average strain over the
length of the indentation measured in 3 mm increments) occurs in the barrier from the imposed
loading.
— Level II: (intermediate protection level) for non-hazardous waste facilities. The “intermediate
protection level” lies between level I protection and the yield of an GBRP. The yield of GBRPs in the
puncture mode is considered as a failure of level II protection. In other words, the liner system is
allowed to have barrier strains greater than 0,25 %, but not if it results in yielding of an GBRP.
[3] [4] [5] [6]
Wilson-Fahmy et al., Narejo et al., Koerner et al. and, more recently, Koerner et al. provide a
basis for protection layer design consistent with this philosophy.
The maximum of 0,25 % local strain (Ԑ ) was proposed by the German “Quo Vadi
...