SIST EN ISO 11274:2020

SLOVENSKI STANDARD
01-januar-2020
Nadomešča:
SIST EN ISO 11274:2014
Kakovost tal - Določevanje karakteristik zadrževanja vode - Laboratorijske metode
(ISO 11274:2019)
Soil quality - Determination of the water-retention characteristic - Laboratory methods
(ISO 11274:2019)
Bodenbeschaffenheit - Bestimmung des Wasserrückhaltevermögens - Laborverfahren
(ISO 11274:2019)
Qualité du sol - Détermination de la caractéristique de la rétention en eau - Méthodes de
laboratoire (ISO 11274:2019)
Ta slovenski standard je istoveten z: EN ISO 11274:2019
ICS:
13.080.40 Hidrološke lastnosti tal Hydrological properties of
soils
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 11274
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2019
EUROPÄISCHE NORM
ICS 13.080.40 Supersedes EN ISO 11274:2014
English Version
Soil quality - Determination of the water-retention
characteristic - Laboratory methods (ISO 11274:2019)
Qualité du sol - Détermination de la caractéristique de Bodenbeschaffenheit - Bestimmung des
la rétention en eau - Méthodes de laboratoire (ISO Wasserrückhaltevermögens - Laborverfahren (ISO
11274:2019) 11274:2019)
This European Standard was approved by CEN on 8 September 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
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 11274:2019 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 11274:2019) has been prepared by Technical Committee ISO/TC 190 "Soil
quality" in collaboration with Technical Committee CEN/TC 444 “Test methods for environmental
characterization of solid matrices” the secretariat of which is held by NEN.
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 April 2020, and conflicting national standards shall be
withdrawn at the latest by April 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 11274:2014.
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 11274:2019 has been approved by CEN as EN ISO 11274:2019 without any modification.

INTERNATIONAL ISO
STANDARD 11274
Second edition
2019-09
Soil quality — Determination of the
water-retention characteristic —
Laboratory methods
Qualité du sol — Détermination de la caractéristique de la rétention
en eau — Méthodes de laboratoire
Reference number
ISO 11274:2019(E)
©
ISO 2019
ISO 11274:2019(E)
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
ii © ISO 2019 – All rights reserved

ISO 11274:2019(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Guidelines for choice of method. 2
4.1 General . 2
4.2 Sand, kaolin or ceramic suction tables for determination of pressures from 0 kPa
to −50 kPa . 2
4.3 Porous plate and burette apparatus for determination of pressures from 0 kPa to
−20 kPa . 2
4.4 Pressure plate extractor for determination of pressures from −5 kPa to −1 500 kPa . 2
4.5 Pressure membrane cells for determination of pressures from −33 kPa to −1 500 kPa . 3
5 Sampling . 3
5.1 General requirements . 3
5.2 Sample preparation . 4
6 Determination of the soil water characteristic using sand, kaolin and ceramic
suction tables . 5
6.1 Principle . 5
6.2 Apparatus . 5
6.3 Preparation of suction tables. 6
6.4 Procedure . 6
6.5 Expression of results . 6
6.5.1 Procedure for soils containing less than 20 % stones (diameter greater
than 2 mm). 6
6.5.2 Conversion of results to a fine soil basis . 7
7 Determination of soil water characteristic using a porous plate and burette .8
7.1 Principle . 8
7.2 Apparatus . 8
7.3 Assembly of porous plate/burette apparatus . 8
7.4 Procedure . 9
7.5 Expression of results . 9
8 Determination of soil water characteristic by pressure plate extractor .11
8.1 Principle .11
8.2 Apparatus .11
8.3 Assembly of apparatus .12
8.4 Procedure .12
8.5 Calculation and expression of results.13
8.5.1 Procedure for stoneless soils .13
8.5.2 Procedure for stony soils .13
9 Determination of soil water characteristic using pressure membrane cells .14
9.1 Principle .14
9.2 Apparatus .14
9.3 Assembly of apparatus .14
9.4 Procedure .15
9.5 Expression of results .16
9.6 Test report .16
10 Test report .16
11 Precision .17
ISO 11274:2019(E)
Annex A (informative) Construction of suction tables .18
Bibliography .23
iv © ISO 2019 – All rights reserved

ISO 11274:2019(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 on 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 the following
URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 3,
Chemical methods and soil characteristics.
This second edition cancels and replaces the first edition (ISO 11274:1998), which has been technically
revised. It also incorporates the Technical Corrigendum ISO 11274:1998/Cor. 1:2009.
ISO 11274:2019(E)
Introduction
Soil water content and matric pressure are related to each other and determine the water-retention
characteristics of a soil. Soil water which is in equilibrium with free water is at zero matric pressure
(or suction) and the soil is saturated. As the soil dries, matric pressure decreases (i.e. becomes more
negative), and the largest pores empty of water. Progressive decreases in matric pressure will continue
to empty finer pores until eventually water is held in only the finest pores. Not only is water removed
from soil pores, but the films of water held around soil particles are reduced in thickness. Therefore a
[9][10]
decreasing matric pressure is associated with a decreasing soil water content . Laboratory or field
measurements of these two parameters can be made and the relationship plotted as a curve, called the
soil water-retention characteristic. The relationship extends from saturated soil (approximately 0 kPa)
to oven-dry soil (about −10 kPa).
The soil water-retention characteristic is different for each soil type. The shape and position of the
curve relative to the axes depend on soil properties such as texture, density and hysteresis associated
with the wetting and drying history. Individual points on the water-retention characteristic may be
determined for specific purposes.
The results obtained using these methods can be used, for example:
— to provide an assessment of the equivalent pore size distribution (e.g. identification of macro- and
micropores);
— to determine indices of plant-available water in the soil and to classify soil accordingly (e.g. for
irrigation purposes);
— to determine the drainable pore space (e.g. for drainage design, pollution risk assessments);
— to monitor changes in the structure of a soil (caused by e.g. tillage, compaction or addition of organic
matter or synthetic soil conditioners);
— to ascertain the relationship between the negative matric pressure and other soil physical properties
(e.g. hydraulic conductivity, thermal conductivity);
— to determine water content at specific negative matric pressures (e.g. for microbiological degradation
studies);
— to estimate other soil physical properties (e.g. hydraulic conductivity).
vi © ISO 2019 – All rights reserved

INTERNATIONAL STANDARD ISO 11274:2019(E)
Soil quality — Determination of the water-retention
characteristic — Laboratory methods
1 Scope
This document specifies laboratory methods for determination of the soil water-retention characteristic.
This document applies only to measurements of the drying or desorption curve.
Four methods are described to cover the complete range of soil water pressures as follows:
a) method using sand, kaolin or ceramic suction tables for determination of matric pressures from
0 kPa to −50 kPa;
b) method using a porous plate and burette apparatus for determination of matric pressures from
0 kPa to −20 kPa;
c) method using a pressurized gas and a pressure plate extractor for determination of matric
pressures from −5 kPa to −1 500 kPa;
d) method using a pressurized gas and pressure membrane cells for determination of matric pressures
from −33 kPa to −1 500 kPa.
Guidelines are given to select the most suitable method in a particular case.
2 Normative references
There are no normative references in this document.
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
soil water-retention characteristic
relation between soil water content and soil matric head of a given soil (sample)
3.2
pressure
pressure equivalent of soil water potential
3.3
matric pressure
amount of work done in order to transport, reversibly and isothermally, an infinitesimal quantity
of water, identical in composition to the soil water, from a pool at the elevation and the external gas
pressure of the point under consideration, to the soil water at the point under consideration, divided by
the volume of water transported
ISO 11274:2019(E)
3.4
water content mass ratio
m
w
mass of water evaporating from the soil when dried to constant mass at 105 °C, divided by the dry mass
of the soil (i.e. the ratio between the masses of water and solid particles within a soil sample)
3.5
water content volume fraction
φ
w
volume of water evaporating from the soil when dried to constant mass at 105 °C, divided by the original
bulk volume of the soil (i.e. the ratio between the volume of liquid water within a soil sample and the
total volume including all pore space of that sample)
Note 1 to entry: The soil water-retention characteristic is identified in the scientific literature by various names
including soil water release curve, soil water-retention curve, pF curve and the capillary pressure-saturation
curve. Use of these terms is deprecated.
Note 2 to entry: The Pascal is the standard unit of pressure but many other units are still in use. Table A.1
provides conversions for most units.
Note 3 to entry: Sometimes suction is used instead of pressure to avoid the use of negative signs (see Introduction).
However, this term can cause confusion and is deprecated as an expression of the matric pressure.
Note 4 to entry: For swelling and shrinking soils, seek the advice of a specialist laboratory since interpretation of
water-retention data will be affected by these properties.
4 Guidelines for choice of method
4.1 General
Guidelines are given below to help selecting the most suitable method in a particular case.
4.2 Sand, kaolin or ceramic suction tables for determination of pressures from 0 kPa
to −50 kPa
The sand, kaolin and ceramic suction table methods are suitable for large numbers of determinations
at high pressures on cores or aggregates of different shapes and sizes. Analyses on samples of a wide
range of textures and organic matter contents can be carried out simultaneously since equilibration is
determined separately for each core. The suction table methods are suitable for a laboratory carrying
out analyses on a routine basis and where regular equipment maintenance procedures are implemented.
4.3 Porous plate and burette apparatus for determination of pressures from 0 kPa
to −20 kPa
The porous plate and burette apparatus allow analysis of only one sample at a time, and several sets
of equipment are therefore necessary to enable replication and full soil profile characterization. The
method is particularly suited to soils with weak structures and sands which are susceptible to slumping
or slaking, since minimal sample disturbance occurs. Capillary contact is not broken during the
procedure and all samples, particularly soils with higher organic matter content or sandy textures, will
equilibrate more rapidly using this technique. This is a simple technique suitable for small laboratories.
4.4 Pressure plate extractor for determination of pressures from −5 kPa to −1 500 kPa
The pressure plate method can be used for determinations of all pressures to −1 500 kPa. However,
different specifications of pressure chambers and ceramic plates are required for the range of pressures,
e.g. 0 kPa to −20 kPa, −20 kPa to −100 kPa and −100 kPa to −1 500 kPa. The method is, however, best
suited to pressures of −33 kPa or lower, since air entrapment at high negative pressures can occur. It is
preferable that soils with similar water-release properties are analysed together to ensure equilibration
2 © ISO 2019 – All rights reserved

ISO 11274:2019(E)
times are approximately the same, though in practice it may be difficult. Sample size is usually smaller
than for the previous two methods and therefore the technique is less suitable for heterogeneous soil
horizons, or for those with a strong structural composition. Analysis of disturbed soils is traditionally
carried out using this method.
4.5 Pressure membrane cells for determination of pressures from −33 kPa to
−1 500 kPa
The pressure membrane cell should only be used for pressures below −33 kPa. Capillary contact at
higher pressures is not satisfactory for this method. The method is appropriate for all soil types though
the use of double membranes is recommended for coarse (sandy) textured soils. Sample size can be
selected (according to the size of the pressure cell) to take into account soil structure. Different textures
can be equilibrated separately using a suite of cells linked to one pressure source.
5 Sampling
5.1 General requirements
It is essential that undisturbed soil samples are used for measurement at the high matric pressure
range 0 kPa to −100 kPa, since soil structure has a strong influence on water-retention characteristics.
Use either undisturbed cores or, if appropriate, individual peds for low matric pressure methods
(<−100 kPa).
Soil cores shall be taken in a metal or plastic sleeve of a height and diameter such that they are
representative of the natural soil variability and structure. The dimensions of samples taken in the field
are dependent on the texture and structure of the soil and the test method to be used. Table 1 provides
guidance on suitable sample sizes for the different methods and soil structure.
Take soil cores carefully to ensure minimal compaction and disturbance to structure, either by hand
pressure in suitable material or by using a suitable soil corer. Take a minimum of three representative
replicates for each freshly exposed soil horizon or layer; more replicates are required in stony soils.
Record the sampling date, sample grid reference, horizon and sampling depths. Dig out the sleeve
carefully with a trowel, trim roughly the two faces of the cylinder with a knife and if necessary, adjust
the sample within the sleeve before fitting lids to each end, and label the top clearly with the sample
grid reference, the direction of the sampling (horizontal or vertical), horizon number and sample depth.
Wrap the samples (e.g. in plastic bags) to prevent drying. Wrap aggregates (e.g.in aluminium foil
or plastic film) to retain structure and prevent drying. Alternatively, excavate blocks measuring
approximately 30 cm cube of undisturbed soil in the field, wrap in metal foil, wax (to retain structure
and prevent drying) and take to the laboratory for subdivision. Store the samples at 1 °C to 2 °C to
reduce water loss and suppress biological activity until they are required for analyses. Treat samples
having obvious macrofaunal activity with a suitable biocide, e.g. 0,05 % copper sulfate solution.
Other relevant site information should be noted, e.g. soil water status, topsoil/surface conditions, etc.
(see 5.2).
Table 1 — Recommended sample sizes (height × diameter) for the different test methods
Dimensions in millimetres
Structure
Test method
Coarse Medium Fine
Suction table 50 × 100 40 × 76 24 × 50
Porous plate 50 × 76 40 × 76 20 × 36
Pressure plate — 10 × 76 10 × 50
ISO 11274:2019(E)
Table 1 (continued)
Structure
Test method
Coarse Medium Fine
Pressure membrane — 20 × 76 10 × 50
NOTE 1 The points mentioned here are specific to water-retention analyses. Reference is made to
ISO 18400-101 in which general advice on sampling and problems encountered is given.
NOTE 2 In moist conditions, soil is easier to sample and in shrink/swell soils the bulk density under natural
conditions is lowest. It is therefore preferable to take samples in the wet season when soil matric pressures are
at or near −5 kPa. Especially clayey soils, are difficult to core when dry and they shrink and swell with varying
water content. Samples of swelling and shrinking soils can be taken in cores only under completely saturated
conditions, i.e. under the water table and in the full capillary zone. In all other circumstances peds can be taken.
5.2 Sample preparation
To prepare samples for water-retention measurements at pressures greater than −50 kPa (see
Clause 3), trim undisturbed cores flush with the ends of the container and replace one lid with a circle
of polyamide (nylon) mesh, similar close-weave material or paper if the water-retention characteristic
is known, secured with an elastic band. The mesh will retain the soil sample in the sleeve and enable
direct contact with the soil and the porous contact medium. Avoid smearing the surface of clayey
soils. Remove any small projecting stones to ensure maximum contact and correct the soil volume if
necessary. Replace the other lid to prevent drying of the sample by evaporation. Prepare soil aggregates
for high matric pressure measurements by levelling one face and wrapping other faces in aluminium
foil to minimize water loss. Disturbed soils should be packed into a sleeve with a mesh attached. Firm
the soil by tapping and gentle pressure to obtain a specified bulk density.
Weigh the prepared samples. Ensure that the samples are brought to a pressure of less than the first
equilibration point by wetting them, if necessary, by capillary rise, mesh side or levelled face down on
a sheet of foam rubber saturated with 0,005 mol/l calcium sulfate solution or tap water. Weigh the
wet sample when a thin film of water is seen on the surface. This water content represents the total or
maximum water-holding capacity and is calculated according to 6.5.
The water-retention characteristic of swelling and shrinking soils should be determined under the
same load as that occurring in the field. Otherwise the laboratory data can deviate from the water-
retention characteristic of the soil under natural field conditions.
The time required for wetting varies with initial soil water content and texture, being a day or two for
sands and two weeks or more for clayey soils. Except for sands, wetting needs to be slow to prevent air
entrapment in samples. Care should be taken not to leave sandy soils wetting for too long because their
structure may collapse. Low-density subsoil sands without the stabilizing influence of organic matter
or roots are the most susceptible. The burette method is most suitable for this type of soil and samples
can be wetted using the procedure in 6.3. Soils should, ideally, be field-moist when the wetting is
commenced; dried soils may cause differences in the water-retention characteristic due to hydrophobia
or hysteresis.
General guidelines for wetting times are:
— Sand 1 d to 5 d
— Loam 5 d to 10 d
— Clay 5 d to 14 d or longer
— Peat 5 d to 20 d
4 © ISO 2019 – All rights reserved

ISO 11274:2019(E)
Increasing temperature causes a decrease in water content at a given pressure. It is recommended
that all water-retention measurements be made at a constant temperature of (20 ± 2) °C. Report the
temperature at which the water-retention measurements are made.
NOTE 1 It can be necessary to discard samples with large projecting stones.
NOTE 2 Very coarse pores are not water-filled when the soil sample is saturated by capillary rise.
6 Determination of the soil water characteristic using sand, kaolin and ceramic
suction tables
6.1 Principle
A negative matric pressure is applied to coarse silt or very fine sand held in a rigid watertight non-
rusting container (a ceramic sink is particularly suitable). Soil samples placed in contact with the
surface of the table lose pore water until their matric pressure is equivalent to that of the suction table.
Equilibrium status is determined by weighing samples on a regular basis and soil water content by
weighing, oven drying and reweighing. The maximum negative pressure which can be applied before
air entry occurs is related to the pore size distribution of the packed fine sand or coarse silt which is
determined by the particle size distribution, the shape of the particles and their consolidation.
6.2 Apparatus
6.2.1 Large ceramic sink or other watertight, rigid, non-rusting container with outlet in base
[dimensions about (50 × 70 × 25) cm] and with close-fitting cover.
6.2.2 Tubing and connecting pieces to construct the draining system for the suction table.
6.2.3 Sand, silt or kaolin, as packing material for the suction table.
Commercially available graded and washed industrial sands with a narrow particle size distribution
are most suitable. The particle size distributions of some suitable sand grades and the approximate
suctions they can attain are given in Table 2. It is permissible to use other packing materials, such as
fine glass beads or aluminium oxide powder, if they can achieve the required air entry values.
6.2.4 Levelling bottle, stopcock and 5 l aspirator bottle.
6.2.5 Tensiometer system (optional).
6.2.6 Drying oven, capable of maintaining a temperature of (105 ± 2) °C.
6.2.7 Balance, capable of weighing with an accuracy of 0,1 % of the measured value.
NOTE Examples of a drainage system, sand and kaolin suction tables and details of their construction are
described in Annex A.
Table 2 — Examples of sands and silica flour suitable for suction tables
Type Coarse sand Medium sand Fine sand Silica flour
Surface of suction Surface of suction ta- Surface of suction ta-
Use Base of suction tables tables (−5 kPa matric bles (−11 kPa matric bles (−21 kPa matric
pressure) pressure) pressure)
Typical particle
Percent content
size distribution
>600 µm 1 1 1 0
ISO 11274:2019(E)
Table 2 (continued)
Type Coarse sand Medium sand Fine sand Silica flour
200 µm to 600 µm 61 8 1 0
100 µm to 200 µm 36 68 11 1
63 µm to 100 µm 1 20 30 9
20 µm to 63 µm 1 3 52 43
<20 µm 0 0 5 47
6.3 Preparation of suction tables
Prepare suction tables using packing material that can attain the required air entry values (see Table 2).
In Annex A the detailed procedure for one specific type of suction table is given as an example.
6.4 Procedure
Prepare soil cores as described in 5.2. Weigh the cores and then place them on a suction table at the
desired matric pressure. Leave the cores for 7 d. The sample is then weighed, and thereafter weighed
as frequently as needed to verify that the daily change in mass of the core is less than 0,02 %. The
sample is then regarded as equilibrated and is moved to a suction table of a lower pressure or oven
dried. Samples which have not attained equilibrium should be replaced firmly onto the suction table
and the table cover replaced to minimize evaporation from the table.
The time for reaching equilibrium is proportional to the square of the height of the sample but, as a
guide, cores normally require at least 7 d to equilibrate at each potential and sometimes 20 days or
more. A minimum of 7 d is recommended so that samples establish good capillary connectivity, enabling
an equilibrium status to be more rapidly attained.
6.5 Expression of results
6.5.1 Procedure for soils containing less than 20 % stones (diameter greater than 2 mm)
6.5.1.1 Calculate the water content mass ratio at a matric pressure p using Formula (1):
m
mp −m
()
md
mp = (1)
()
wm
m
d
where
m (p ) is the water content mass ratio at a matric pressure p , in grams;
w m m
m(p ) is the mass of the soil sample at a matric pressure p , in grams;
m m
m is the mass of the oven-dried soil sample, in grams;
d
6.5.1.2 Calculate the water content on volume basis at matric pressure p using Formula (2):
m
mp −m
()
md
ϕ p = (2)
()
w m
V ⋅ρ
w
where
6 © ISO 2019 – All rights reserved

ISO 11274:2019(E)
φ (p ) is the water content volume fraction at a matric pressure p , in cubic centimetre water
w m m
per cubic centimetre soil;
m(p ) is the mass, in grams of the soil sample at a matric pressure p ;
m m
m is the mass of the oven-dried soil sample, in grams;
d
V is the volume of the soil sample, in cubic centimetre;
−3
ρ is the density of water, in grams per cubic centimetre (= 1 g ⋅ cm ).
w
If a containing sleeve, mesh and elastic band are used, these should be weighed and their weights
deducted from the total weight of the soil core to give m(p ).
m
NOTE The water content volume fraction is related to the water content mass ratio as follows:
b
m
ρs
d
ϕ pm= p =mp
() () ()
wwmm w m
V ⋅ρρ
w w
where
m (p ) is the water content mass ratio at a matric pressure p , in grams water per gram soil;
w m m
b is the bulk density of the oven-dried soil, in grams per cubic centimetre.
ρs
6.5.2 Conversion of results to a fine soil basis
The stone content of a laboratory soil sample may not accurately represent the field situation and
therefore conversion of data to a fine soil basis may be required for comparison of results or for
correction to a field-measured stone content. If conversion of results derived from vacuum or suction
methods to a fine soil basis (f) is required for soils containing stones, Formula (3) shall be used:
ϕ
t
ϕ = (3)
f
1−ϕ
()
s
where
φ is the water content of the fine soil, expressed as a fraction of volume;
f
φ is the volume of stones, expressed as a fraction of total core volume;
s
φ is the water content of the total soil, expressed as a fraction of total core volume.
t
Thus in a soil containing 0,05 total core volume fraction of nonporous stones Formula (4) shall be used:
ϕ
t
ϕ = (4)
f
10− ,05
()
Porous stones retain water and require a different correction: Determine the water content of porous
stones at each matric pressure and correct the water content of the soil accordingly; thus in a soil
containing 0,05 total core volume fraction of porous stones Formula (5) shall be used:
ϕϕ−⋅00, 5
()
ts
ϕ = (5)
f
09, 5
where φ is the water content of the porous stones, expressed as a fraction of the total porous stone
s
volume in the soil sample.
ISO 11274:2019(E)
In soils containing many very porous stones, the stones should be considered as part of the soil mass,
and φ is not distinguished from φ .
f t
NOTE For mixtures of porous and nonporous stones, as in clay soils containing both flint and chalk
fragments, correct the total soil value for both stone types.
7 Determination of soil water characteristic using a porous plate and burette
7.1 Principle
A negative matric pressure is applied to a glass Buchner funnel containing a porous ceramic plate by
means of a hanging water column. The minimum pressure which can be applied depends on the air-
entry pressure of the plate. In practice the minimum pressure applied is restricted by the distance to
which the levelling burette may be lowered below the funnel, typically less than 2 m. Only one sample
can be treated per Buchner funnel. The increase in volume of water in the burette is equivalent to the
soil water which has drained from the soil sample. Equilibrium status is determined by observing the
burette and not by weighing the sample. The soil sample is weighed and oven-dried to determine the
water content at the final matric pressure.
NOTE It is also possible to determine the adsorption curve as the sample is wetted.
The diameter and height of the Buchner funnel should be of sufficient size to accommodate the soil
core. The ceramic plate should fit the internal diameter of the Buchner funnel. A bubbling pressure of
100 kPa is suggested for all measurements carried out with this apparatus, though requirements may
vary and bubbling pressures lower than this may be used.
7.2 Apparatus
7.2.1 Buchner funnel.
7.2.2 Porous ceramic plate.
7.2.3 Flexible watertight tubing.
7.2.4 Graduated burette.
The volume of the burette and increment divisions should be chosen with due consideration of the
size of the sample, the particle size distribution and density, and the negative matric pressure applied.
A 50-ml-burette with 0,1 ml increments is appropriate for a soil sample of 300 cm volume.
7.2.5 Drying oven, capable of maintaining a temperature of (105 ± 2) °C.
7.2.6 Balance, capable of weighing accurately to 0,01 g.
7.2.7 Rubber stoppers and connector.
7.3 Assembly of porous plate/burette apparatus
Connect the bottom of the burette to the bottom of the Buchner funnel. Connect the stopper at the
top of the burette to the stopper at the top of the Buchner funnel with the flexible nylon tubing to
prevent evaporation, as shown in Figure 1. Fill the tubing and funnel with de-aerated water and adjust
the burette until the water is level with the ceramic plate. Remove trapped air bubbles by tapping the
apparatus or by applying gentle air pressure through the end of the burette, then apply a vacuum to the
open end of the burette and draw de-aerated water downwards through the plate until all air bubbles
are removed. Alternatively, remove air bubbles from beneath the porous plate by raising the water level
to the top of the funnel, stopper the funnel and insert it.
8 © ISO 2019 – All rights reserved

ISO 11274:2019(E)
7.4 Procedure
Place a pre-wetted undisturbed soil core on the water-saturated plate. Maintain the water level at the
same height as the ceramic plate until the sample is saturated and then record the volume of water
in the burette. Adjust the burette so that the water level in it is h cm below the middle of the sample.
The negative matric pressure (p in kilopascals) is equivalent to −(p /10). Adjust the burette when a
m m
reading at a defined pressure is required. Equilibrium water content is reached when the water gain
in the burette is less than 0,05 % of the volume of the soil sample per day. Then read the volume in the
burette and repeat the whole procedure for each desired pressure in decreasing order. The volume of
water which is withdrawn from the soil sample is equal to the change in volume of water in the burette.
Weigh the soil core at the final matric pressure when equilibrated, oven dry and reweigh.
7.5 Expression of results
7.5.1 Procedure for soils containing less than 20 % stones (diameter greater than 2 mm)
7.5.2 Calculate the water content volume fraction at
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