Design using geosynthetics — Part 4: Drainage

This document outlines the criteria for evaluating the available and the required flow rate of geosynthetics in various situations, provides a summary of the available laboratory testing, and lists the safety factors and reduction factors that can be applied to the parameters when designing using geosynthetics for drainage systems.

Design pour géosynthétiques — Partie 4: Drainage

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TECHNICAL ISO/TR
REPORT 18228-4
First edition
2022-03
Design using geosynthetics —
Part 4:
Drainage
Design pour géosynthétiques —
Partie 4: Drainage
Reference number
ISO/TR 18228-4:2022(E)
© ISO 2022
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ISO/TR 18228-4:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

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ISO/TR 18228-4:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms, definitions and symbols .......................................................................................................................................................... 1

3.1 Symbols and abbreviations ......................................................................................................................................................... 1

4 Concepts ........................................................................................................................................................................................................................ 6

5 Applications ..............................................................................................................................................................................................................8

6 Materials ....................................................................................................................................................................................................................... 9

6.1 Components of draining geocomposites ......................................................................................................................... 9

6.2 Filter Component of draining geocomposites ............................................................................................................. 9

6.3 Drainage cores ..................................................................................................................................................................................... 10

6.4 Definitions and acronyms for the various products .......................................................................................... 10

7 Properties relevant to design .............................................................................................................................................................10

8 Darcy’s law...............................................................................................................................................................................................................10

9 Subsurface drainage structures .......................................................................................................................................................11

10 Geosynthetic properties ...........................................................................................................................................................................11

11 Geotextile filter performance and filter criteria ...........................................................................................................12

12 Geocomposite drainage systems design..................................................................................................................................12

12.1 General ........................................................................................................................................................................................................12

12.2 Calculation of input flow rate .................................................................................................................................................13

12.2.1 General .....................................................................................................................................................................................13

12.2.2 Rainfall on sloping surface ..................................................................................................................................... 13

12.2.3 Filtration from soil or rock ..................................................................................................................................... 16

12.3 Calculation of available flow rate........................................................................................................................................ 17

12.3.1 Hydraulic gradient ......................................................................................................................................................... 17

12.3.2 Discharge capacity ......................................................................................................................................................... 19

12.3.3 Pressure applied to the geocomposite ......................................................................................................... 19

12.3.4 Materials in contact with the faces of the drainage geocomposite .................................... 21

12.3.5 Compressive behaviour of geocomposites ...............................................................................................22

12.3.6 Factors influencing the available flow rate ............................................................................................. 24

12.3.7 Laboratory tests for water flow capacity of geocomposites ....................................................25

12.3.8 Specific situations .......................................................................................................................................................... 27

12.3.9 Flow rate versus hydraulic gradient ..............................................................................................................29

12.3.10 Flow rate versus viscosity ...................................................................................................................................... 31

12.3.11 General procedure for evaluating the available flow rate of the

geocomposites ................................................................................................................................................................... 33

12.4 Selection of the geocomposite ...............................................................................................................................................34

12.5 Equivalence with a granular drainage layer .............................................................................................................34

12.5.1 General .....................................................................................................................................................................................34

12.5.2 Equivalence for water flow on slopes ...........................................................................................................34

12.5.3 Equivalence for vertical water flow ...............................................................................................................39

Annex A (informative) The movement of water in the ground .............................................................................................41

Annex B (informative) Reduction factors ....................................................................................................................................................53

Bibliography .............................................................................................................................................................................................................................60

iii
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ISO/TR 18228-4:2022(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.
A list of all parts in the ISO 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.
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ISO/TR 18228-4:2022(E)
Introduction

The ISO 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 characterization 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 drainage function. Details of design methodology

adopted in a number of regions are provided.
[10]

Parts of this document have been adapted from Comité français des géosynthétiques, 2014 .

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TECHNICAL REPORT ISO/TR 18228-4:2022(E)
Design using geosynthetics —
Part 4:
Drainage
1 Scope

This document outlines the criteria for evaluating the available and the required flow rate of

geosynthetics in various situations, provides a summary of the available laboratory testing, and lists

the safety factors and reduction factors that can be applied to the parameters when designing using

geosynthetics for drainage systems.
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, definitions and symbols

For the purposes of this document, the terms and definitions given in ISO 10318-1 and the following

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/
3.1 Symbols and abbreviations
O characteristic opening size of a geosynthetic (µm)
k coefficient of permeability normal to the plane(m/s)
q flux(l/m ⋅s)
v-index velocity index(mm/s)
ψ permittivity(s )
ϑ transmissivity (m /s/m or l/s/m)
GCD acronym used for draining geocomposites
dQ/dt volumetric flow rate of water through the soil (m /s or l/s)
A bulk cross-sectional area through which the flow occurs (m )
h hydraulic head (m)
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ISO/TR 18228-4:2022(E)
l distance travelled by the bulk water flow (m)
dh/dl hydraulic gradient (dimensionless)
K hydraulic conductivity or permeability of the soil (m/s)
q equal to (dQ/dt), volumetric flow rate (m /s or l/s)
i equal to (dh/dl), hydraulic gradient (dimensionless)

q in-plane flow capacity, equal to the volumetric flow rate of water and/or other liquids

per unit width of specimen, at defined gradients in the plane of a product (l/s⋅m).

k coefficient of permeability in the plane, equal to the ratio between in-plane flow capacity

q and the product of thickness d and hydraulic gradient i (m/s)
3 2
q rainfall per unit horizontal area (m /s/m )
P rainfall flow rate (m /s)
A horizontal area (m )
3 2
q rainfall per unit sloping area (m /s/m )
β slope angle (deg or °)
3 2
q rainfall per unit area entering the drainage system (m /s/m )
f coefficient of infiltration (dimensionless)
Q input flow rate due to rainfall (m /s/m or l/s/m)
L length of the slope (m)
L horizontal length of the slope (m)
h height of rainfall (mm)
t duration of the rainfall (h)
j rainfall intensity (mm/h)
a parameter of the pluviometric curve (mm h )
n exponent of the pluviometric curve (-)
F , Factor of Safety on input flow rate (dimensionless)
S Q
Q input flow rate due to additional surficial flow (m /s/m or l/s/m)
Q design input flow rate in the geocomposite (m /s/m or l/s/m)
Q total rainfall flow on the catchment zone (m /s or l/s)
A horizontal area of the catchment zone (m )
B running width of the geocomposite drain (m)
h maximum thickness of liquid in the granular liquid collection layer
max
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Q Specific flow rate = discharge per unit width in the geocomposite, under a specified

hydraulic gradient (m /s/m or l/s/m)
B width of geocomposite specimen in the flow rate test (m)
q measured flow rate for a geocomposite specimen of width B (l/s or m /s)
p applied pressure (kPa)

γ saturated unit weight of the soil or material placed on the geocomposite (kN/m )

H thickness of the soil or the material placed on the geocomposite (m)
w distributed surcharge on the ground surface (kPa)
H depth of the lowest point of the geocomposite below the ground surface (m)
K coefficient of active pressure of the soil (dimensionless)
φ friction angle of the soil (deg or °)
t, t geocomposite thickness (m)
GCD
L distance between geotextile support points (m)
Q specific flow rate for the i gradient (l/s/m or m /s)
i1 1
Q specific flow rate for the i gradient (l/s/m or m /s)
i0 0

i hydraulic gradient on the diagram, immediately higher than the actual hydraulic gra-

dient (dimensionless)
i actual hydraulic gradient (dimensionless)
Q discharge or volumetric flow rate (m /s)
A cross-sectional area of the geocomposite (m )
1/2
χ parameter depending on the roughness of the flow surface (m / s)
R hydraulic radius of the flow conduit (m)
C parameter as a function of geometry and roughness of the flow surface
σ pressure applied in lab tests (kPa)
i , i hydraulic gradients applied in lab tests (dimensionless)
1 2
i actual hydraulic gradient (dimensionless)
Q(σ , i) flow rate evaluated for the values σ , i (l/s/m or m /s)
n n
Q (σ , i ) flow rate evaluated for the values σ , i (l/s/m or m /s)
i0 n 0 n 0
Q , Q specific flow rates at 20 °C and T °C
20 T
μ , μ viscosity of water at 20 °C and T °C
20 T
T actual temperature of water (°C)
C correction factor for temperature and viscosity (dimensionless)
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Q available long term flow rate for the geocomposite (l/s/m or m /s)

Q short term flow rate obtained from laboratory tests with the appropriate boundary

conditions (l/s/m or m /s)

R Reduction Factor for the intrusion of filter geotextiles into the draining core due to tensile

F,in

creep of the geotextile, occurring after the short term flow rate test (dimensionless)

R Reduction Factor for the compressive creep of the geocomposite (dimensionless)
F,cr-Q
R Reduction Factor for chemical clogging of the draining core (dimensionless)
F,cc
R Reduction Factor for biological clogging of the draining core (dimensionless)
F,bc

R Reduction Factor for overall uncertainties on laboratory data and field conditions

F,L
(dimensionless)
3 2
q flow rate of liquid supply (m /s/m )
j factor of the Giroud theory (dimensionless)
t prescribed thickness of the granular layer (m)
prescribed
F Factor of Safety on equivalency (dimensionless)
S,E
E equivalency coefficient (dimensionless)

Q minimum short term input flow rate for the geocomposite in order to be considered

GCD

equivalent to the granular layer having thickness larger than h (m /s/m or l/s/m)

max
Q flow rate in the granular soil layer according to Darcy’s law (m /s/m)
Darcy

K long term permeability of the granular soil layer evaluated in situ at the end of its

design life (m/s)
* 3 2

q equivalent flow rate of liquid supply in the granular soil layer at equilibrium (m /s/m )

j* factor of the Giroud theory related to Q (dimensionless)
Darcy
E* equivalency coefficient for the thickness t (dimensionless)
prescribed

Q * short term input flow rate for the geocomposite in order to be considered equivalent

GCD
to the granular layer having thickness t (m /s/m)
prescribed
Q flow rate afforded by the granular drainage layer (m /s/m or l/s/m)
U Darcy's velocity (m/s)
z vertical distance in the soil (m)

k intrinsic permeability of the soil, which depends only on properties of the solid matrix

(m )
2 4 3
ρ density of the fluid (N s /m or kg/m )
μ dynamic viscosity of the fluid (N / m s)
C Hazen's empirical coefficient for intrinsic permeability (dimensionless)
-1 -1
C* Hazen's empirical coefficient for permeability (m s )
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C coefficient of uniformity of the soil = D / D (dimensionless)
U 60 10
D , D diameter of soil particles for 10 % and 60 % cumulative passing (m)
10 60
g acceleration due to gravity = 9,81 m/s
γ unit weight of water for the given temperature (kN/m )
n soil porosity = void volume / total volume (dimensionless)

R Reduction Factor for the intrusion of filter geotextiles into the draining core for Rigid

F,in(R/R) short term
/ Rigid boundaries at short term (dimensionless)

R Reduction Factor for the intrusion of filter geotextiles into the draining core for Soft /

F,in(R/S) short term
Soft boundaries at short term (dimensionless)

R Reduction Factor for the intrusion of filter geotextiles into the draining core for Rigid

F,in(S/S) short term
/ Soft boundaries at short term (dimensionless)

R Reduction Factor for the intrusion of filter geotextiles into the draining core for Rigid

F,in(R/R) long term
/ Rigid boundaries at long term (dimensionless)

R Reduction Factor for the intrusion of filter geotextiles into the draining core for Soft /

F,in(R/S) long term
Soft boundaries at long term (dimensionless)

R Reduction Factor for the intrusion of filter geotextiles into the draining core for Rigid

F,in(S/S) long term
/ Soft boundaries at long term (dimensionless)

Q Specific flow rate for Rigid / Rigid boundaries at short term (m /s/m or l/s/m)

L (R/R) short term
Q Specific flow rate for Rigid / Soft boundaries at short term (m /s/m or l/s/m)
L (R/S) short term
Q Specific flow rate for Soft / Soft boundaries at short term (m /s/m or l/s/m)
L (S/S) short term
Q Specific flow rate for Rigid / Rigid boundaries at long term (m /s/m or l/s/m)
L (R/R) long term
Q Specific flow rate for Rigid / Soft boundaries at long term (m /s/m or l/s/m)
L (R/S) long term
Q Specific flow rate for Soft / Soft boundaries at long term (m /s/m or l/s/m)
L (S/S) long term
R Reduction Factor for thickness (dimensionless)
F,cr,th
t thickness of the geocomposite core before load application (m);
virgin

t thickness measured at long term (1 year, 10 years, ... 100 years) in compressive creep

tests (m)

q(σ , i, long term) long term available flow rate for applied pressure σ and hydraulic gradient i (m /s/m

n n
or l/s/m);

q(σ , i) short term available flow rate for applied pressure σ and hydraulic gradient i (m /s/m

n n
or l/s/m);
x(σ , 0) short term thickness of geocomposite for applied pressure σ (m);
n n
x(σ , t) long term thickness of geocomposite for applied pressure σ (m);
n n
F Reduction Factor for thickness (dimensionless)

α Reduction Factor for the long term effect of compressive creep and geotextile intrusion

(dimensionless)
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ISO/TR 18228-4:2022(E)
Q long term flow rate (m /s/m or l/s/m)
long term
4 Concepts

Some types of geosynthetics, particularly geocomposites, can be used as planar drainage medium in

subsurface drainage systems.

The design of planar drainage geosynthetics requires hydraulic and geotechnical concepts for defining

the design input flow rates, and a detailed method for defining the allowable long-term flow of

geosynthetics, based on laboratory testing.

Drainage geosynthetics typically consist of a continuous drainage core (geonet, geomat, geospacer)

capable of transporting a fluid along its own plane, and geotextiles and/or geomembranes, coupled to

the drainage core, which prevent the drainage core itself from being clogged by the surrounding soil.

The components of a draining geocomposite with continuous draining core are filtering geotextiles (on

one or both sides), draining core and geomembrane, as shown in Figure 1.

Some geocomposites available on the market include discrete draining elements, such as small diameter

pipes, instead of a continuous draining core (Figure 2). In this type of geocomposite, the geotextiles act

as a filter and also contribute to carrying the water flow. In general, the water flow capacity provided

by geotextiles is very small compared to that provided by the discrete draining elements.

Drainage geosynthetics are widely used in controlled landfills, roads, railways, airports, tunnels and

buildings. Drainage systems with geosynthetics are used within a performance envelope between the

extreme cases of drainage along a sub-horizontal plane and along a vertical plane; between a hydraulic

gradient close to 0 and a hydraulic gradient of 1.

In addition to the hydraulic gradient, the draining capacity of a geocomposite depends on the pressure

applied and the materials in contact with the two faces.

The design of a drainage system with geosynthetics is based on the evaluation of the drainage capacity

available under actual operating conditions and on the flow rate required by the project.

The drainage capacity can be assessed on the basis of appropriate laboratory tests, while the required

flow rate is evaluated on the basis of hydrological and hydraulic considerations.

Key
1 geotextile
2 draining core
3 geomembrane

Figure 1 — Components of a draining geocomposite with continuous draining core: 1) Draining

core + geotextile; 2) Geotextile + draining core + geotextile; 3) Geotextile + draining core +

geomembrane
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ISO/TR 18228-4:2022(E)
Key
1 discrete draining elements
2 geotextile
Figure 2 — Draining geocomposite with discrete draining elements
a b e f
c d
Key
a separation function
b filtration function
c protection function
d barrier function
e drainage function
f drainage systems applications

Figure 3 — Functions and Applications of drainage geocomposites (Source: ISO 10318-2)

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ISO/TR 18228-4:2022(E)
Key
1 plastic core
2 geotextile
3 protects waterproofing from damage
4 distributes pressure
5 retains its drainage capacity even under high earth pressure
6 transports water to the collector drain
7 removes excess water from the soil
8 prevents the collector drain from silting up with fine soil particles
Figure 4 — Principles of the functions afforded by drainage geocomposites
5 Applications

Drainage geocomposites are made from a plastic drainage core that is thermally or otherwise bonded

to a geotextile on one or both sides or to a waterproofing layer on one side.

They are capable of providing one or more main functions within the application as a drainage system,

shown in Figure 3. The principles of the functions offered by drainage geocomposites are illustrated in

Figure 4.
The main applications of planar drainage geocomposites are the following:
— Drainage of concrete walls
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ISO/TR 18228-4:2022(E)
— Drainage of reinforced soil structures
— Drainage in road, railway and airport applications

— Horizontal drainage and capillary break layer in embankments made up of fine and cohesive fill

— Drainage trenches

— Leachate collection and gas ventilation in landfill applications (also used as a protection layer

against geomembrane puncturing)
— Drainage of rainfall water infiltration in landfill applications
— Drainage in natural and artificial tunnel applications
— Drainage layer in roofing and deck pavement applications
— Drainage of sport fields
6 Materials
6.1 Components of draining geocomposites

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 element.

— The filtering component can have the following characteristics under operating conditions: adequate

permeability to gases and liquids in the direction perpendicular to the filter plane

— retention capacity of the soil particles

The draining component may have the following characteristics under operating conditions:

— 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
6.2 Filter Component of draining geocomposites

The filters are typically made up of nonwoven geotextiles, yet in certain specific applications some

types of woven fabrics are occasionally used. The most commonly used nonwoven geotextiles are:

— staple fibres nonwoven, mechanically needled;
— continuous fibres nonwoven, thermally bonded or mechanically needled.

The physico-mechanical properties of nonwoven geotextiles are qualitatively as follows:

— Staple or continuous filament fibres needle-punched (only) nonwoven:
— Relatively high thickness
— High compressibility
— Highly deformable over time
— Potential clogging both on the surface and internally and limited blinding
— Staple fibres needle-punched and thermocalandered non-woven:
— Moderate thickness
— Moderate compressibility
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ISO/TR 18228-4:2022(E)
— Moderate deformability over time

— Potential clogging both on the surface and internally and blinding risk on the heat-bonded

surface and limited blinding on the other face
— Continuous fibres heat-bonded nonwoven:
— Lowest thickness
— Very low compressibility
— Slightly deformable over time
— Blinding risks
6.3 Drainage cores
The drainage cores are characterized by a three-dimensional structure with
...

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