Soil quality — Determination of the water-retention characteristic — Laboratory methods

Specifies laboratory methods for determination of the soil water-retention characteristic. This standard 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 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 pressure from -5 kPa to -1500 kPa; d) method using a pressurized gas and pressure membrane cells for determination of matric pressures from -33 kPa to -1500 kPa. Guidelines are given to select the most suitable method in a particular case.

Qualité du sol — Détermination de la caractéristique de la rétention en eau — Méthodes de laboratoire

Kakovost tal – Določevanje zadrževanja vode – Laboratorijske metode

Ta mednarodni standard opredeljuje laboratorijske metode za določevanje značilnosti tal, ki zadržujejo vodo. Ta mednarodni standard velja zgolj za meritve krivulje za sušenje ali za desorpcijo. Z namenom zajeti celoten razpon pritiskov vode na tla, so opisane štiri metode, kot sledi:
a) metoda, ki uporablja peščene, kaolinske ali keramične sesalne plošče za določevanje pritiska od 0 kPa do -50 kPa;
b) metoda, ki uporablja porozno ploščo in bireto za določevanje matričnih tlakov od 0 kPa do -20 kPa;
b) metoda, ki uporablja plin pod tlakom in ploščo v tlačnem ekstraktorju za določevanje matričnih tlakov od 5 kPa do -1500 kPa;
b) metoda, ki uporablja plin pod tlakom in membrane tlačnim celic za določevanje matričnih tlakov od 33 kPa do -1500 kPa.
Podane so smernice za izbiro najbolj primerne metode v posameznem primeru.

General Information

Status
Withdrawn
Publication Date
17-Jun-1998
Withdrawal Date
17-Jun-1998
Current Stage
9599 - Withdrawal of International Standard
Completion Date
21-Sep-2019

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Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 11274
First edition
1998-07-01
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
A
Reference number
ISO 11274:1998(E)

---------------------- Page: 1 ----------------------
ISO 11274:1998(E)
Contents Page
1 Scope . 1
2 Definitions . 1
3 Guidelines for choice of method . 2
4 Sampling . 3
Determination of the soil water characteristic using sand,
5
kaolin and ceramic suction tables . 5
6 Determination of soil water characteristic using a porous
plate and burette. 8
7 Determination of soil water characteristic by pressure
plate extractor. 11
8 Determination of soil water characteristic using pressure
membrane cells . 13
9 Precision . 15
Annexes .
A (informative)  Construction of suction tables . 16
B (informative)  Bibliography. 20
©  ISO 1998
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet iso@iso.ch
Printed in Switzerland
ii

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©
ISO ISO 11274:1998(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.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard ISO 11274 was prepared by Technical Committee
ISO/TC 190, Soil quality, Subcommittee SC 5, Physical methods.
Annexes A and B of this International Standard are for information only.
iii

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ISO 11274:1998(E) ISO
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 decreasing matric pressure is associated with a
decreasing soil water content [5], [6]. 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
6
saturated soil (approximately 0 kPa) to oven-dry soil (about 210 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).
iv

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INTERNATIONAL STANDARD  ISO ISO 11274:1998(E)
Soil quality — Determination of the water-retention
characteristic — Laboratory methods
1  Scope
This International Standard specifies laboratory methods for determination of the soil water-retention characteristic.
This International Standard 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 - 1500 kPa;
d) method using a pressurized gas and pressure membrane cells for determination of matric pressures from
- 33 kPa to - 1500 kPa.
Guidelines are given to select the most suitable method in a particular case.
2  Definitions
For the purposes of this International Standard, the following definitions apply.
2.1
soil water-retention characteristic
relation between soil water content and soil matric head of a given soil sample
2.2
matric pressure
amount of work that must be 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
1

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ISO 11274:1998(E)
2.3
water content mass ratio
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)
2.4
water content volume fraction
q
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  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  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  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  For swelling and shrinking soils, seek the advice of a specialist laboratory since interpretation of water-retention data
will be affected by these properties.
3  Guidelines for choice of method
Guidelines are given below to help select the most suitable method in a particular case.
3.1  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.
3.2  Porous plate and burette apparatus for determination of pressures from 0 kPa to – 20 kPa
The porous plate and burette apparatus allows 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.
3.3  Pressure plate extractor for determination of pressures from – 5 kPa to – 1500 kPa
The pressure plate method can be used for determinations of all pressures to - 1500 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 1500 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 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.
2

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ISO
ISO 11274:1998(E)
3.4  Pressure membrane cells for determination of pressures from – 33 kPa to – 1500 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.
4  Sampling
4.1  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 properties. 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 which is 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 stoney 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.
Table 1 — Recommended sample sizes (height 3 diameter) for the different test methods
Dimensions in millimetres
Test Structure
method
Coarse Medium Fine
Suction table 50 3 100 40 3 76 24 3 50
Porous plate 50 3 76 40 3 76 20 3 36
Pressure plate 10 3 76 10 3 50
Pressure membrane 20 3 76 10 3 50
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ISO 11274:1998(E)
NOTE 1 The points mentioned here are specific to water-retention analyses. Reference is made to ISO 10381-1 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. Dry
conditions should be avoided, especially for clayey soils, which are both difficult to core when dry and contract 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 should be taken.
NOTE 3 Other relevant site information should be noted, e.g. soil water status, topsoil/surface conditions, etc. (see clause 5.6).
4.2  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 de-aerated tap water or 0,005 mol/l calcium sulfate solution. 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 clause 6.5.
Report the temperature at which the water-retention measurements are made.
NOTE 1  It may be necessary to discard samples with large projecting stones. The chemical composition of the wetting fluid
can affect the water-retention characteristic, particularly in fine-textured soils with swelling clays. Wetting with distilled or freshly
drawn tap water is not generally recommended. De-aerated 0,005 mol/l calcium sulfate solution is suggested to represent the
chemical composition of the soil solution.
NOTE 2  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 to 5 days
loam 5 to 10 days
clay 5 to 14 days or longer
peat 5 to 20 days.
NOTE 3  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. Where temperature control is not available, the
laboratory temperature should be monitored as the work is conducted, and reported in the test report.
NOTE 4  Very coarse pores are not water-filled when the soil sample is saturated by capillary rise.
NOTE 5  Water can be de-aerated by boiling for 5 min. It should be stored cool in a stoppered vessel.
NOTE 6  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.
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ISO 11274:1998(E)
5  Determination of the soil water characteristic using sand, kaolin and ceramic suction
tables
5.1  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.
5.2  Apparatus
5.2.1  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.
5.2.2  Tubing and connecting pieces to construct the draining system for the suction table.
5.2.3  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.
5.2.4  Levelling bottle, stopcock and 5-litre aspirator bottle.
5.2.5  Tensiometer system (optional).
5.2.6  Drying oven, capable of maintaining a temperature of (105 – 2) °C.
5.2.7  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
Use Base of suction Surface of suction Surface of suction Surface of suction
tables tables (5 kPa matric tables (11 kPa matric tables (21 kPa matric
pressure) pressure) pressure)
Typical particle size Percent content
distribution
> 600 μm 1 1 1 0
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
5

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ISO 11274:1998(E)
5.3  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.
5.4  Procedure
Prepare soil cores as described in 4.2. Weigh the cores and then place them on a suction table at the desired matric
pressure. Leave the cores for 7 days. 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.
NOTE  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 days to equilibrate at each potential and sometimes 20 days or more. A minimum of 7 days is
recommended so that samples establish good capillary connectivity, enabling an equilibrium status to be more rapidly attained.
5.5  Expression of results
5.5.1  Procedure for soils containing less than 20 % stones (diameter greater than 2 mm)
5.5.1.1  Calculate the water content mass ratio at a matric pressure p using the formula:
m
mp()−m
m d
wp()=
m
m
d
where
w(p ) is the water content mass ratio at a matric pressure p , in grams;
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
5.5.1.2  Calculate the water content on volume basis at matric pressure p using the formula:
m
mp()−m
m d
q()p =
m
V× r
w
where
u(p ) is the water content volume fraction at a matric pressure p , in cubic centimetres water per cubic
m m
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 centimetres;
-3
r is the density of water, in grams per cubic centimetre (= 1 g cm ).
w
NOTE 1  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 n(p ).
m
NOTE 2  The water content volume fraction is related to the water content mass ratio as follows:
b
r

m
d s
q()p =w(p) =w()p
mm m
V × r r
w w
6

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ISO
ISO 11274:1998(E)
where
w(p ) is the water content mass ratio at a matric pressure p , in grams water per gram soil;
m m
b
r is the bulk density of the oven-dried soil, in grams per cubic centimetre.
s
5.5.2  Conversion of results to a fine earth basis
The stone content of a laboratory soil sample may not accurately represent the field situation and therefore
conversion of data to a fine earth 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 earth basis (f) is
required for soils containing stones, the following method shall be used:
q
t
q
=
f
(1− q )
s
where:
q is the water content of the fine earth, expressed as a fraction of volume;
f
q is the volume of stones, expressed as a fraction of total core volume;
s
q is the water content of the total earth, expressed as a fraction of total core volume.
t
Thus in a soil containing 0,05 total core volume fraction of nonporous stones:
q
t
q =
f
(1− 0,05)
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
qq−×( 0,05)
ts
q=
f
09, 5
where:
q is the water content of the porous stones, expressed as a fraction of the total porous stone volume in the
s
soil sample.
NOTE 1  In soils containing many very porous stones, it is recommended that the stones be considered as part of the soil
mass, and q is not distinguished from q .
f t
NOTE 2  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.
5.6  Test report
The test report shall include the following information:
a) a reference to this International Standard;
b) a reference to the method used;
c) complete identification of the sample:
7

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ISO 11274:1998(E)
- grid reference of the sample location
- date of field sampling
- soil moisture conditions
- depth of sampling
- number of samples per determination
- size of samples
- condition of sample - undisturbed soil core/aggregate, disturbed,
 sieved, porous stone, etc.
- wetting fluid used
- temperature and range at which determinations were made;
d) the results of the determinations:
- water contents at each pressure determined as total or fine earth fraction and expressed clearly as either:
1) volume fraction
2) mass ratio
or, if water contents at several pressures using the same soil sample have been determined:
3) plot the results as a water-retention characteristic
- details of any curve-fitting method that has been applied.
e) any details not specified in this International Standard or regarded as optional, as well as any factor which may
have affected the results.
6  Determination of soil water characteristic using a porous plate and burette
6.1  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 1  It is also possible to determine the adsorption curve as the sample is wetted.
NOTE 2  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.
6.2  Apparatus
6.2.1  Buchner funnel
6.2.2  Porous ceramic plate
6.2.3  Flexible watertight tubing
6.2.4  Graduated burette
NOTE  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
3
appropriate for a soil sample of 300 cm volume.
6.2.5  Drying oven, capable of maintaining a temperature of (105 ± 2) °C
6.2.6  Balance, capable of weighing accurately to 0,01 g
6.2.7  Rubber stoppers and connector
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6.3  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.
6.4  Procedure
Place a prewetted 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 wate
...

SLOVENSKI STANDARD
SIST ISO 11274:2006
01-september-2006
.DNRYRVWWDO±'RORþHYDQMH]DGUåHYDQMDYRGH±/DERUDWRULMVNHPHWRGH
Soil quality - Determination of the water-retention characteristic - Laboratory methods
Ta slovenski standard je istoveten z:
ICS:
13.080.40 Hidrološke lastnosti tal Hydrological properties of
soils
SIST ISO 11274:2006 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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INTERNATIONAL ISO
STANDARD 11274
First edition
1998-07-01
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
A
Reference number
ISO 11274:1998(E)

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ISO 11274:1998(E)
Contents Page
1 Scope . 1
2 Definitions . 1
3 Guidelines for choice of method . 2
4 Sampling . 3
Determination of the soil water characteristic using sand,
5
kaolin and ceramic suction tables . 5
6 Determination of soil water characteristic using a porous
plate and burette. 8
7 Determination of soil water characteristic by pressure
plate extractor. 11
8 Determination of soil water characteristic using pressure
membrane cells . 13
9 Precision . 15
Annexes .
A (informative)  Construction of suction tables . 16
B (informative)  Bibliography. 20
©  ISO 1998
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet iso@iso.ch
Printed in Switzerland
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©
ISO ISO 11274:1998(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.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard ISO 11274 was prepared by Technical Committee
ISO/TC 190, Soil quality, Subcommittee SC 5, Physical methods.
Annexes A and B of this International Standard are for information only.
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ISO 11274:1998(E) ISO
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 decreasing matric pressure is associated with a
decreasing soil water content [5], [6]. 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
6
saturated soil (approximately 0 kPa) to oven-dry soil (about 210 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).
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INTERNATIONAL STANDARD  ISO ISO 11274:1998(E)
Soil quality — Determination of the water-retention
characteristic — Laboratory methods
1  Scope
This International Standard specifies laboratory methods for determination of the soil water-retention characteristic.
This International Standard 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 - 1500 kPa;
d) method using a pressurized gas and pressure membrane cells for determination of matric pressures from
- 33 kPa to - 1500 kPa.
Guidelines are given to select the most suitable method in a particular case.
2  Definitions
For the purposes of this International Standard, the following definitions apply.
2.1
soil water-retention characteristic
relation between soil water content and soil matric head of a given soil sample
2.2
matric pressure
amount of work that must be 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
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ISO 11274:1998(E)
2.3
water content mass ratio
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)
2.4
water content volume fraction
q
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  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  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  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  For swelling and shrinking soils, seek the advice of a specialist laboratory since interpretation of water-retention data
will be affected by these properties.
3  Guidelines for choice of method
Guidelines are given below to help select the most suitable method in a particular case.
3.1  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.
3.2  Porous plate and burette apparatus for determination of pressures from 0 kPa to – 20 kPa
The porous plate and burette apparatus allows 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.
3.3  Pressure plate extractor for determination of pressures from – 5 kPa to – 1500 kPa
The pressure plate method can be used for determinations of all pressures to - 1500 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 1500 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 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.
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3.4  Pressure membrane cells for determination of pressures from – 33 kPa to – 1500 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.
4  Sampling
4.1  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 properties. 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 which is 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 stoney 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.
Table 1 — Recommended sample sizes (height 3 diameter) for the different test methods
Dimensions in millimetres
Test Structure
method
Coarse Medium Fine
Suction table 50 3 100 40 3 76 24 3 50
Porous plate 50 3 76 40 3 76 20 3 36
Pressure plate 10 3 76 10 3 50
Pressure membrane 20 3 76 10 3 50
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NOTE 1 The points mentioned here are specific to water-retention analyses. Reference is made to ISO 10381-1 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. Dry
conditions should be avoided, especially for clayey soils, which are both difficult to core when dry and contract 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 should be taken.
NOTE 3 Other relevant site information should be noted, e.g. soil water status, topsoil/surface conditions, etc. (see clause 5.6).
4.2  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 de-aerated tap water or 0,005 mol/l calcium sulfate solution. 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 clause 6.5.
Report the temperature at which the water-retention measurements are made.
NOTE 1  It may be necessary to discard samples with large projecting stones. The chemical composition of the wetting fluid
can affect the water-retention characteristic, particularly in fine-textured soils with swelling clays. Wetting with distilled or freshly
drawn tap water is not generally recommended. De-aerated 0,005 mol/l calcium sulfate solution is suggested to represent the
chemical composition of the soil solution.
NOTE 2  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 to 5 days
loam 5 to 10 days
clay 5 to 14 days or longer
peat 5 to 20 days.
NOTE 3  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. Where temperature control is not available, the
laboratory temperature should be monitored as the work is conducted, and reported in the test report.
NOTE 4  Very coarse pores are not water-filled when the soil sample is saturated by capillary rise.
NOTE 5  Water can be de-aerated by boiling for 5 min. It should be stored cool in a stoppered vessel.
NOTE 6  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.
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ISO 11274:1998(E)
5  Determination of the soil water characteristic using sand, kaolin and ceramic suction
tables
5.1  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.
5.2  Apparatus
5.2.1  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.
5.2.2  Tubing and connecting pieces to construct the draining system for the suction table.
5.2.3  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.
5.2.4  Levelling bottle, stopcock and 5-litre aspirator bottle.
5.2.5  Tensiometer system (optional).
5.2.6  Drying oven, capable of maintaining a temperature of (105 – 2) °C.
5.2.7  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
Use Base of suction Surface of suction Surface of suction Surface of suction
tables tables (5 kPa matric tables (11 kPa matric tables (21 kPa matric
pressure) pressure) pressure)
Typical particle size Percent content
distribution
> 600 μm 1 1 1 0
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
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5.3  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.
5.4  Procedure
Prepare soil cores as described in 4.2. Weigh the cores and then place them on a suction table at the desired matric
pressure. Leave the cores for 7 days. 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.
NOTE  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 days to equilibrate at each potential and sometimes 20 days or more. A minimum of 7 days is
recommended so that samples establish good capillary connectivity, enabling an equilibrium status to be more rapidly attained.
5.5  Expression of results
5.5.1  Procedure for soils containing less than 20 % stones (diameter greater than 2 mm)
5.5.1.1  Calculate the water content mass ratio at a matric pressure p using the formula:
m
mp()−m
m d
wp()=
m
m
d
where
w(p ) is the water content mass ratio at a matric pressure p , in grams;
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
5.5.1.2  Calculate the water content on volume basis at matric pressure p using the formula:
m
mp()−m
m d
q()p =
m
V× r
w
where
u(p ) is the water content volume fraction at a matric pressure p , in cubic centimetres water per cubic
m m
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 centimetres;
-3
r is the density of water, in grams per cubic centimetre (= 1 g cm ).
w
NOTE 1  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 n(p ).
m
NOTE 2  The water content volume fraction is related to the water content mass ratio as follows:
b
r

m
d s
q()p =w(p) =w()p
mm m
V × r r
w w
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ISO 11274:1998(E)
where
w(p ) is the water content mass ratio at a matric pressure p , in grams water per gram soil;
m m
b
r is the bulk density of the oven-dried soil, in grams per cubic centimetre.
s
5.5.2  Conversion of results to a fine earth basis
The stone content of a laboratory soil sample may not accurately represent the field situation and therefore
conversion of data to a fine earth 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 earth basis (f) is
required for soils containing stones, the following method shall be used:
q
t
q
=
f
(1− q )
s
where:
q is the water content of the fine earth, expressed as a fraction of volume;
f
q is the volume of stones, expressed as a fraction of total core volume;
s
q is the water content of the total earth, expressed as a fraction of total core volume.
t
Thus in a soil containing 0,05 total core volume fraction of nonporous stones:
q
t
q =
f
(1− 0,05)
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
qq−×( 0,05)
ts
q=
f
09, 5
where:
q is the water content of the porous stones, expressed as a fraction of the total porous stone volume in the
s
soil sample.
NOTE 1  In soils containing many very porous stones, it is recommended that the stones be considered as part of the soil
mass, and q is not distinguished from q .
f t
NOTE 2  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.
5.6  Test report
The test report shall include the following information:
a) a reference to this International Standard;
b) a reference to the method used;
c) complete identification of the sample:
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- grid reference of the sample location
- date of field sampling
- soil moisture conditions
- depth of sampling
- number of samples per determination
- size of samples
- condition of sample - undisturbed soil core/aggregate, disturbed,
 sieved, porous stone, etc.
- wetting fluid used
- temperature and range at which determinations were made;
d) the results of the determinations:
- water contents at each pressure determined as total or fine earth fraction and expressed clearly as either:
1) volume fraction
2) mass ratio
or, if water contents at several pressures using the same soil sample have been determined:
3) plot the results as a water-retention characteristic
- details of any curve-fitting method that has been applied.
e) any details not specified in this International Standard or regarded as optional, as well as any factor which may
have affected the results.
6  Determination of soil water characteristic using a porous plate and burette
6.1  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 1  It is also possible to determine the adsorption curve as the sample is wetted.
NOTE 2  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.
6.2  Apparatus
6.2.1  Buchner funnel
6.2.2  Porous ceramic plate
6.2.3  Flexible watertight tubing
6.2.4  Graduated burette
NOTE  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
3
appropriate for a soil sample of 300 cm volume.
6.2.5  Drying oven, capable of maintaining a temperature of (105 ± 2) °C
6.2.6  Balance, capable of weighing accurately to 0,01 g
6.2.7  Rubber stoppers and connector
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6.3  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 vacuu
...

NORME ISO
INTERNATIONALE 11274
Première édition
1998-07-01
Qualité du sol — Détermination de la
caractéristique de la rétention en eau —
Méthodes de laboratoire
Soil quality — Determination of the water-retention characteristic —
Laboratory methods
A
Numéro de référence
ISO 11274:1998(F)

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ISO 11274:1998(F)
Sommaire Page
1 Domaine d'application . 1
2 Définitions . 1
3 Lignes directrices pour le choix de la méthode. 2
4 Échantillonnage . 3
Détermination de la caractéristique de rétention en eau
5
du sol à l'aide de tables à succion à sable, à kaolin et
à plaque en céramique . 5
6 Détermination de la caractéristique de rétention en eau du sol
en utilisant une plaque poreuse et une burette. 8
7 Détermination de la caractéristique en eau du sol par
l'extracteur à plaque de pression. 11
Détermination de la caractéristique en eau du sol par
8
l'utilisation d'enceinte à membrane sous pression. 14
9 Fidélité . 16
Annexes .
A (informative)  Construction de tables à succion . 17
B (informative)  Bibliographie .
22
©  ISO 1998
Droits de reproduction réservés. Sauf prescription différente, aucune partie de cette publi-
cation ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun pro-
cédé, électronique ou mécanique, y compris la photocopie et les microfilms, sans l'accord
écrit de l'éditeur.
Organisation internationale de normalisation
Case postale 56 • CH-1211 Genève 20 • Suisse
Internet iso@iso.ch
Imprimé en Suisse
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ISO ISO 11274:1998(F)
Avant-propos
L'ISO (Organisation internationale de normalisation) est une fédération
mondiale d'organismes nationaux de normalisation (comités membres de
l'ISO). L'élaboration des Normes internationales est en général confiée aux
comités techniques de l'ISO. Chaque comité membre intéressé par une
étude a le droit de faire partie du comité technique créé à cet effet. Les
organisations internationales, gouvernementales et non gouvernementales,
en liaison avec l'ISO participent également aux travaux. L'ISO collabore
étroitement avec la Commission électrotechnique internationale (CEI) en
ce qui concerne la normalisation électrotechnique.
Les projets de Normes internationales adoptés par les comités techniques
sont soumis aux comités membres pour vote. Leur publication comme
Normes internationales requiert l'approbation de 75 % au moins des
comités membres votants.
La Norme internationale ISO 11274 a été élaborée par le comité technique
ISO/TC 190, Qualité du sol, sous-comité SC 5, Méthodes physiques.
Les annexes A et B de la présente Norme internationale sont données
uniquement à titre d'information.
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Introduction
La teneur en eau du sol et la pression matricielle sont deux phénomènes
liés qui déterminent les caractéristiques de la rétention en eau d'un sol.
L'eau présente dans le sol en équilibre avec l'eau libre est la pression
matricielle (ou succion) égale à zéro, le sol est donc saturé. À mesure que
le sol sèche, la pression matricielle décroît (c'est-à-dire qu'elle devient
négative), et les pores les plus grands se vident de l'eau qu'ils contiennent.
La diminution progressive de la pression matricielle va contribuer à vider
de leur eau des pores de plus en plus petits, jusqu'à ce que l'eau ne
remplisse plus que les pores les plus fins. L'eau est non seulement
éliminée des pores du sol, mais l'épaisseur des pellicules d'eau qui
entourent les particules du sol diminue également. Aussi, la diminution de
la pression matricielle correspond-elle à une diminution de la teneur en eau
du sol [5], [6]. Il est possible de mesurer ces deux paramètres en
laboratoire ou sur le terrain, et d'établir leur relation en traçant la courbe
correspondant à la caractéristique de rétention en eau du sol. Cette
relation s'étend des sols saturés (0 kPa environ) aux sols desséchés en
6
étuve (environ - 10 kPa).
La caractéristique de la rétention en eau du sol est différente pour chaque
type de sol. La forme et la position de la courbe sur un repère orthonormé
sont fonction des propriétés du sol, telles que sa texture, sa densité,
l'hystérésis associée aux phases d'humidification et de séchage. Il est
possible de définir, à des fins spécifiques, certains points de la courbe
caractérisant la rétention d'eau.
Il est possible d'utiliser les résultats obtenus à l'aide de ces méthodes pour,
par exemple:
— évaluer la répartition des pores par tailles (par exemple: identification
des pores macroscopiques et microscopiques);
— attribuer des niveaux correspondant à l'eau disponible dans le sol pour
la culture des plantes et classer les sols en conséquence (à des fins
d'irrigation, par exemple);
— déterminer l'espace poral drainable (par exemple pour concevoir un
système de drainage ou évaluer les risques de pollution);
— surveiller tout changement dans la structure d'un sol (provoqué, par
exemple, par les travaux agricoles, la compaction ou l'addition de
matières organiques ou de traitements artificiels);
— vérifier la relation entre la pression matricielle négative et les autres
propriétés physiques du sol (comme la conductivité hydraulique ou
thermique, par exemple);
— déterminer la teneur en eau correspondant à des pressions
matricielles négatives spécifiques (dans le cadre d'une étude de la
dégradation microbiologique, par exemple);
— évaluer d'autres propriétés physiques du sol (comme la conductivité
hydraulique, par exemple).
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NORME INTERNATIONALE  ISO ISO 11274:1998(F)
Qualité du sol — Détermination de la caractéristique de la
rétention en eau — Méthodes de laboratoire
1  Domaine d'application
La présente Norme internationale décrit les méthodes de laboratoire permettant de déterminer les caractéristiques
de rétention en eau du sol.
La présente Norme internationale s'applique uniquement aux mesurages effectués pour établir les courbes de
séchage et de désorption.
Il existe quatre méthodes pour prendre en compte l'ensemble du domaine des pressions de l'eau des sols, à savoir:
a) méthode utilisant des tables à succion à sable, kaolin ou céramique permettant de déterminer des pressions
matricielles comprises entre 0 kPa et - 50 kPa;
b) méthode associant une plaque poreuse à un appareillage à burette pour déterminer des pressions matricielles
comprises entre 0 kPa et - 20 kPa;
c) méthode utilisant un gaz sous pression et un extracteur à plaque poreuse permettant de déterminer des
pressions matricielles comprises entre - 5 kPa et - 1 500 kPa;
d) méthode utilisant un gaz sous pression et des cellules à membranes sous pression pour déterminer des
pressions matricielles comprises entre - 33 kPa et - 1 500 kPa;
Des lignes directrices sont données à l'article 3 pour faciliter le choix de la méthode la mieux adaptée à chaque cas
particulier.
2  Définitions
Pour les besoins de la présente Norme internationale, les définitions suivantes s'appliquent.
2.1
caractéristique de la rétention en eau du sol
rapport entre la teneur en eau du sol et la pression matricielle d'un échantillon de sol donné
2.2
pression matricielle
quantité de travail nécessaire au transport, de façon réversible et isotherme, d'une quantité infinitésimale d'eau, de
composition identique à celle présente dans le sol, d'un point dont l'altitude et la pression gazeuse externe sont
identiques à celles du point considéré, dans l'eau du sol, au point considéré, divisée par le volume d'eau transporté
2.3
teneur en eau rapportée à la masse
w
masse d'eau s'évaporant du sol lorsqu'il est séché à 105 °C jusqu'à obtention d'une masse constante, divisée par la
masse de sol sec (soit le rapport entre masse d'eau et particules solides dans un échantillon de sol)
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2.4
fraction volumique de la teneur en eau
q
volume d'eau, s'évaporant du sol lorsqu'il est séché à 105 °C jusqu'à obtention d'une masse constante, divisée par
le volume apparent initial du sol (soit le rapport entre le volume d'eau, sous forme liquide contenu dans un
échantillon de sol, et le volume total de cet échantillon, espace poral compris)
NOTES
1  La caractéristique de la rétention en eau du sol apparaît dans la documentation scientifique sous des noms différents,
comme la courbe de libération d'eau du sol, courbe de rétention en eau du sol, courbe pF ou encore courbe de pression
capillaire à saturation. L'utilisation de ces termes est déconseillée.
2  Le pascal est l'unité de pression normalisée. Néanmoins, de nombreuses autres unités continuent d'être utilisées. Le
tableau A.1 permet de convertir en pascals la plupart de ces unités.
3  Dans certains cas, on préfère parler de succion au lieu de pression pour éviter d'utiliser des signes négatifs (voir
Introduction). Cependant, en raison des confusions qui peuvent s'ensuivre, il est déconseillé d'utiliser ce terme, et
particulièrement lorsqu'il s'agit de la pression matricielle.
4  Pour les sols présentant des phénomènes de gonflement ou de retrait, demander conseil à un laboratoire spécialisé, les
données relatives à la rétention en eau étant affectées par ces propriétés.
3  Lignes directrices pour le choix de la méthode
3.1  Tables à succion à sable, kaolin ou céramique pour appliquer des pressions allant de 0 kPa
à – 50 kPa
Les méthodes utilisant des tables à succion à sable, kaolin ou céramique conviennent à des déterminations en
grand nombre, effectuées à des pressions élevées, sur des échantillons non remaniés ou des granulats de formes
et de tailles différentes. Il est possible d'analyser simultanément des échantillons de textures et de teneurs en
matières organiques très diverses, la mise à l'équilibre étant déterminée séparément pour chaque échantillon. Ces
méthodes utilisant des tables à succion sont recommandées dans le cadre de laboratoires qui effectuent des
analyses périodiques et mettent régulièrement en œuvre des procédures d'entretien du matériel.
3.2  Appareillage à burette associé à une plaque poreuse pour appliquer des pressions allant de
0 kPa à – 20 kPa
Ce dispositif associant un appareillage à burette à une plaque poreuse ne permet d'analyser qu'un seul échantillon
à la fois. Il est donc nécessaire de disposer de plusieurs dispositifs de ce genre pour permettre la réplication des
mesures et fournir ainsi une description complète du profil du sol. En raison du faible risque pour ces échantillons
d'être perturbés, cette méthode convient particulièrement aux sols peu structurés, ainsi qu'aux sables susceptibles
de s'affaisser ou d'absorber rapidement de l'eau. Ce mode opératoire préserve les contacts capillaires et permet à
tous les échantillons de sol, et particulièrement à ceux ayant une forte teneur en matières organiques ou ayant une
texture sableuse, d'atteindre plus rapidement l'équilibre. Il s'agit d'une technique simple, à la portée des petits
laboratoires.
3.3  Extracteur à plaque poreuse pour appliquer des pressions allant de – 5 kPa à – 1 500 kPa
Si cette méthode utilisant une plaque poreuse peut être utilisée pour déterminer n'importe quelle pression jusqu'à
- 1 500 kPa, les spécifications relatives aux chambres de pression et aux plaques en céramique peuvent être
différentes selon la plage de pression, par exemple de 0 kPa à 20 kPa, de 20 kPa à 100 kPa, et de 100 kPa à
1 500 kPa. Cependant, en raison des phénomènes d'intrusion d'air qui peuvent se produire à des pressions
négatives élevées, cette méthode convient mieux aux pressions inférieures ou égales à - 33 kPa. Il est préférable
d'analyser des sols ayant des propriétés hydrique comparables, pour obtenir des temps de mise en équilibre à peu
près égaux, bien que, dans la pratique, cela présente des difficultés. La taille des échantillons analysés par cette
méthode est en général inférieure à celle des échantillons analysés par les deux méthodes précédentes, ce qui
rend cette méthode peu adaptée à l'analyse d'horizons de sol hétérogènes, ou à celle de sols fortement structurés.
Traditionnellement, on utilise cette méthode pour analyser des échantillons de sol perturbés.
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3.4  Cellules à membrane sous pression pour appliquer des pressions allant de – 33 kPa
à – 1 500 kPa
Il convient de réserver l'utilisation des cellules à membrane sous pression à des pressions inférieures à - 33 kPa. À
des pressions plus élevées, le contact capillaire nécessaire à cette méthode n'est pas satisfaisant. Si cette méthode
peut être utilisée quel que soit le type de sol, il est recommandé d'utiliser des membranes doubles pour faire des
mesures sur des sols à texture grossière (sableuse). La dimension de l'échantillon peut être choisie en fonction de
la structure du sol (tout en tenant compte de la taille de la cellule de pression). Des textures différentes peuvent être
mises en équilibre séparément à l'aide d'une série de cellules liées à un même dispositif de mise sous pression.
4  Échantillonnage
4.1  Prescriptions générales
Il est essentiel d'utiliser des échantillons de sol non perturbés pour effectuer des mesurages à des pressions
matricielles élevées, comprises entre 0 kPa et - 100 kPa, la structure du sol ayant une influence prépondérante sur
ses propriétés de rétention en eau. Pour les méthodes utilisant des pressions matricielles plus basses
(< - 100 kPa), utiliser des carottes non perturbées ou, le cas échéant, des agrégats élémentaires.
Les carottes doivent être prélevées dans le sol à l'aide d'un cylindre en métal ou en plastique, dont la hauteur et le
diamètre sont choisis dans le souci d'obtenir une carotte représentative de la diversité et de la structure du sol
étudié. Les dimensions des échantillons prélevés sur le site sont fonction de la texture et de la structure du sol, ainsi
que de la méthode d'essai retenue. Le tableau 1 donne des conseils relatifs aux dimensions des échantillons en
fonction de la méthode et de la structure du sol.
Les carottes doivent être prélevées dans le sol avec soin, pour éviter de les compacter ou d'en modifier la structure,
soit à la main, à l'aide d'un outil adapté, soit en utilisant un préleveur approprié. Prélever au minimum trois
échantillons représentatifs de chaque horizon ou couche de sol récemment ouvert. S'agissant de sols rocailleux,
prélever un plus grand nombre d'échantillons. Consigner dans un rapport la date d'échantillonnage, la référence de
l'échantillon sur la grille d'échantillonnage du site, l'horizon dont il s'agit ainsi que la profondeur d'échantillonnage.
Remonter avec précaution le cylindre à l'aide d'une truelle, égaliser grossièrement les deux extrémités à l'aide d'un
couteau et, le cas échéant, ajuster l'échantillon dans le manchon avant de fixer un couvercle à chaque extrémité, et
apposer sur l'extrémité supérieure une étiquette mentionnant la référence de l'échantillon sur la grille
d'échantillonnage du site, le sens de l'échantillonnage (vertical ou horizontal), le numéro de l'horizon et la
profondeur où l'échantillon a été prélevé.
Emballer les échantillons dans une feuille d'aluminium ou dans un sac en plastique par exemple, pour qu'ils
conservent leur structure et ne se dessèchent pas. Il est également possible d'excaver sur le site des cubes de sol
non remué, de 30 cm de côté environ, de les emballer dans une feuille d'aluminium, ou dans de la paraffine (pour
préserver leur structurer et les empêcher de se dessécher) et de les emporter au laboratoire pour les subdiviser.
Stocker les échantillons à une température comprise entre 1 °C et 2 °C pour éviter les pertes d'eau et inhiber
l'activité biologique en attendant le moment de les analyser. Traiter les échantillons présentant une activité macro-
faunique évidente à l'aide d'un biocide approprié, par exemple une solution de sulfate de cuivre à 0,05 %.
NOTES
1  Les points mentionnés ici concernent spécifiquement les analyses de la rétention en eau. On se reportera à l'ISO 10381-1
qui donne des conseils généraux pour l'échantillonnage et les problèmes rencontrés.
2  Il est plus facile d'échantillonner un sol dans des conditions humides. S'agissant de sols sujets au gonflement et au retrait,
la masse volumique apparente la plus faible correspond à celle obtenue dans des conditions naturelles. Il est donc déconseillé
de prélever les échantillons à la saison humide, lorsque les pressions matricielles du sol sont de l'ordre de - 5 kPa. Il est
conseillé d'éviter des conditions climatiques sèches, particulièrement dans le cas de sols argileux dans lesquels il est difficile
de prélever des carottes et dont le volume varie en fonction de la teneur en eau. Des échantillons de sol sujets au gonflement
et au retrait peuvent être prélevés, mais uniquement sous forme de cylindre, dans des conditions de saturation complète, c'est-
à-dire sous la nappe phréatique ou dans la zone de frange capillaire. Dans tous les autres cas, il convient de prélever des
agrégats élémentaires.
3  Il convient de noter toute information pertinente relative au site comme l'état de l'eau présente dans le sol, l'état de la
couche arable et de la surface, etc. (voir 5.6).
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Tableau 1 — Dimensions recommandées pour les échantillons (hauteur · diamètre) selon
la méthode d'essai retenue
Dimensions en millimètres
Méthode d'essai Structure
Grossière Moyenne Fine
Table à succion 50 · 100 40 · 76 24 · 50
Plaque poreuse 50 · 76 40 · 76 20 · 36
Plaque de pression 10 · 76 10 · 50
Membrane sous pression 20 · 76 10 · 50
4.2  Préparation de l'échantillon
Pour préparer les échantillons destinés aux mesurages de rétention en eau à des pressions supérieures à - 50 kPa
(voir article 3), égaliser les deux extrémités du cylindre de sol non perturbé et refermer l'une des extrémités à l'aide
d'un filet en polyamide (nylon), ou tout autre tissage serré, ou encore avec du papier, retenu à l'aide d'un bracelet
élastique, si la teneur en eau est connue. Le filet assure le maintien de l'échantillon dans le manchon tout en
permettant un contact direct entre le sol et le milieu poreux. Éviter de lisser la surface des sols argileux. Éliminer
tous les petits cailloux saillants pour assurer une surface de contact maximale et corriger, si nécessaire, le volume
en conséquence. Replacer l'autre couvercle pour éviter le dessèchement des échantillons par évaporation. Pour
des mesurages à une pression matricielle élevée, préparer les agrégats du sol en égalisant l'une des faces et en
enveloppant les autres dans une feuille d'aluminium, pour réduire au minimum les pertes en eau. Il est conseillé
d'emballer les échantillons de sol perturbé dans un manchon fermé par un filet. Compacter le sol en le tapotant et
en exerçant une légère pression afin d'obtenir la masse volumique apparente spécifiée.
Peser les échantillons préparés. Vérifier que les échantillons ont bien été amenés à une pression inférieure au
premier point d'équilibre en les humidifiant, si nécessaire, par capillarité: l'extrémité prisonnière du filet, ou
l'extrémité égalisée, étant en contact avec une plaque de caoutchouc mousse saturée d'eau du robinet désaérée,
ou, de préfrence, d'une solution de sulfate de calcium à 0,005 mol/l. Peser l'échantillon humide au moment où une
fine pellicule d'eau apparaît à la surface. Cette teneur en eau correspond à la capacité de rétention en eau
maximale ou totale, et se calcule conformément à 6.5.
Consigner dans un rapport la température à laquelle les mesurages de la rétention en eau ont été effectués.
NOTES
1  Il peut s'avérer nécessaire de rejeter les échantillons présentant de gros cailloux saillants. La composition chimique du
fluide de mouillage peut affecter la caractéristique de rétention en eau, particulièrement lorsqu'il s'agit de sols à texture fine ou
contenant de l'argile susceptible de gonfler. En général, il est recommandé de ne pas utiliser de l'eau distillée ou de l'eau du
robinet pour mouiller les échantillons. On suggère d'utiliser une solution de sulfate de calcium désaérée à 0,005 mol/l, plus
représentative de la composition du liquide présent dans le sol.
2  Le temps nécessaire pour humecter les échantillons varie en fonction de la teneur en eau initiale et de la structure du sol, et
peut aller d'un jour ou deux pour les sables, à deux semaines ou plus, pour les sols argileux. Pour empêcher les inclusions
d'air, le mouillage doit être relativement lent, sauf pour le sable. Il convient de veiller à ne pas prolonger l'humectation des sols
sableux en raison des risques d'effondrement de leur structure. Les sables de sous-sol de faible masse volumique, et qui ne
sont pas stabilisés par des racines ou des matières organiques, sont les plus exposés à ce risque. La méthode de la burette
associée à une plaque poreuse est la mieux adaptée à ce type de sols et les échantillons peuvent être humectés selon la
procédure décrite en 6.3. Il convient que, lors de leur humectation, les sols aient conservé leur humidité naturelle. Les
phénomènes d'hydrophobie et d'hystérésis peuvent, dans le cas de sols desséchés, modifier la caractéristique de rétention en
eau.
Les durées de mouilllage conseillées sont en général:
pour le sable: de 1 j à 5 j
pour la terre glaise: de 5 j à 10 j
pour les sols argileux: de 5 j à 14 j et plus
pour la tourbe: de 5 j à 20 j.
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3  Toute augmentation de température peut entraîner une diminution de la teneur en eau à une pression donnée. Il est
recommandé d'effectuer tous les mesurages relatifs à la rétention en eau à une température constante de (20 – 2) °C. À défaut
d'un thermostat, il convient de contrôler régulièrement la température du laboratoire pendant la durée des travaux et de la
consigner dans le rapport d'essai.
4  Lorsque la saturation de l'échantillon se fait par capillarité, les pores les plus grossiers ne se remplissent pas d'eau.
5  Il est possible de désaérer l'eau en la faisant bouillir pendant 5 min. Il convient de la conserver au frais dans un récipient
fermé.
6  La caractéristique de rétention en eau des sols sujets au gonflement et au retrait doit normalement être déterminée sous
une charge identique à celle supportée in situ. Sinon, les données obtenues en laboratoire pour la caractéristique de rétention
en eau peuvent s'écarter de celles obtenues dans les conditions naturelles prévalant sur le site.
5  Détermination de la caractéristique de rétention en eau du sol à l'aide de tables à
succion à sable, à kaolin et à plaque en céramique
5.1  Principe
Une pression matricielle négative est appliquée à du limon grossier ou à du sable très fin, contenu dans un récipient
rigide, étanche et inoxydable (un évier en céramique est particulièrement adapté). Les échantillons de sols se
trouvant au contact de la table perdent l'eau contenue dans leurs pores jusqu'à ce que leur pression matricielle soit
identique à celle de la table. Le moment où l'équilibre est atteint est déterminé en pesant régulièrement les
échantillons de sol, et la teneur en eau est déterminée en les pesant, en les séchant à l'étuve et en les pesant de
nouveau. La pression négative maximale qui peut être appliquée, avant qu'une entrée d'air se produise, est fonction
de la répartition des pores par tailles du sable fin ou du limon grossier compacté, répartition qui est elle même
fonction de la granulométrie, de la forme des particules et de leur compaction.
5.2  Appareillage
5.2.1  Grand évier en céramique, ou tout autre récipient rigide, étanche et inoxydable, muni d'un trou d'évacuation
(ayant les dimensions 50 cm · 70 cm · 25 cm) et d'un bouchon hermétique.
5.2.2  Tubes et raccords permettant de construire un système de drainage pour la table à succion.
5.2.3  Sable, limon ou kaolin, utilisés comme matériau de remplissage pour la table à succion.
Les sables les mieux adaptés sont les sables industriels triés et lavés, d'une granulométrie étroite et vendus dans le
commerce. Les granulométries de certaines qualités de sables adaptées, et la vapeur approximative de la succion
qui leur est associée, figurent dans le tableau 2. Il est admis d'utiliser d'autres matériaux de remplissage, tels que
de petites billes de verre ou de la poudre d'oxyde d'aluminium, à condition qu'ils puissent atteindre les valeurs
requises pour le point d'entrée d'air.
5.2.4  Flacon pour maintenir le niveau à l'équilibre, muni d'un robinet et flacon aspirateur de 5 l.
5.2.5  Tensiomètre (facultatif).
5.2.6  Étuve de séchage, à température constante de (105 – 2) °C.
5.2.7  Balance, de précision de l'ordre de 0,1 % de la valeur mesurée.
NOTE  L'annexe A propose des exemples de système d'écoulement, de tables en sable et kaolin et précise les détails de leur
fabrication.
5.3  Préparation des tables à succion
Préparer les tables à succion en utilisant du matériau de remplissage pouvant atteindre les valeurs requises pour
les points d'entrée d'air (voir tableu 2). L'annexe A propose en exemple le mode opératoire détaillé à suivre pour un
modèle particulier de table à succion.
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Tableau 2 — Exemples de sables et farine de silice pour tables à succion
Type Sable grossier Sable moyen Sable fin Farine de silice
Utilisation Base des tables Surface des tables Surface des tables Surface des tables
de succion de succion de succion de succion
(succion de 5 kPa) (succion de 11 kPa) (succion de 21 kPa)
Répartition Teneur en pourcentage
granulométrique type
> 600 μm 1 1 1 0
200 μm à 600 μm 61 8 1 0
100 μm à 200 μm 36 68 11 1
63 μm à 100 μm 1 20 30 9
20 μm à 63 μm 1 3 52 43
< 20 μm 0 0 5 47
5.4  Mode opératoire
Préparer des cylindres de sol conformément aux indications données en 4.2. Peser les cylindres et les placer sur
une table à succion ayant atteint la pression matricielle souhaitée. Laisser reposer les échantillons pendant 7 j.
Peser ensuite un échantillon, et le peser aussi souvent que nécessaire pour vérifier quotidiennement que la masse
de l'éprouvette reste identique à 0,02 % près. Si tel est le cas, considérer l'échantillon comme étant à l'équilibre et le
poser sur une table à succion ayant une pression inférieure, ou bien le sécher en étuve. Il convient que les
échantillons n'ayant pas atteint l'équilibre soient de nouveau replacés fermement sur la table à succion dont le
revêtement a été remis en place pour réduire au maximum les risques d'évaporation de la table.
NOTE  Le temps nécessaire pour atteindre des conditions d'équilibre est proportionnel au carré de la hauteur de l'échantillon,
mais on peut également dire que les carottes nécessitent normalement, pour s'équilibrer à chaque potentiel, un minimum de
7 j, et parfois même, 20 j ou plus. Il est recommandé de respecter un minimum de 7 j pour laisser aux échantillons le temps
nécessaire pour établir un contact capillaire satisfaisant, permettant d'atteindre plus rapidement l'état d'équilibre.
5.5  Expression des résultats
5.5.1  Mode opératoire pour les sols contenant moins de 20 % de cailloux (de taille supérieure à 2 mm).
5.5.1.1  Calculer le rapport entre la masse et la teneur en eau, à une pression matricielle, p , à l'aide de la formule
m
suivante:
mp()−m
m
d
wp()=
m
m
d

w(p ) est le rapport de la masse à la teneur en eau, à la pression matricielle p .
m m
m(p ) est la masse de l'échantillon de sol, en grammes, à la pression matricielle p .
m m
m est la masse de l'échantillon de sol séché en étuve, en grammes.
d
5.5.1.2  Calculer la teneur volumique en eau, à la pression matricielle p , à l'aide de la formule suivante:
m
mp()−m
m d
q()p =
m
V× r
w

q(p ) est la teneur volumique en eau, à la pression matricielle p , en centimètres cubes d'eau par
m m
centimètre cube (de sol);
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©
ISO
ISO 11274:1998(F)
m(p ) est la masse de l'échantillon de sol, à la pression matricielle p , en grammes;
m m
m est la masse de l'échantillon de sol séché en étuve, en grammes;
d
V est le volume de l'échantillon de sol, en centimètres cubes;
. -3
r est la masse volumique de l'eau, en grammes par centimètres cubes (= 1 g cm ).
w
NOTES
1  Pour obtenir m(p ), il convient de peser les manchons, filet et bracelet élastique éventuellement utilisés et de déduire leurs
m
masses de la masse totale de la carotte de sol.
2  La teneur volumique en eau est liée au rapport de la masse à la teneur en eau, par la relation suivante:
b
r
m
d s
q()p =w(p) =w()p
mm m
r r
V ×
w w

w(p ) est le rapport de la masse à la teneur en eau, à la pression matricielle p , en grammes d'eau par granme de sol;
m m
b
r est la masse volumique apparente du sol séché en étuve, en grammes par centimètre cube.
s
5.5.2  Conversion des résultats pour ne prendre en compte que la terre fine
Il arrive que la teneur en cailloux d'un échantillon de sol pour laboratoire ne soit pas représentative de la situation in
situ. Il peut donc s'avérer nécessaire de convertir les données en ne tenant compte que de la terre fine pour
permettre la comparaison des résultats ou pour les corriger de la teneur en cailloux mesurée in situ. Pour convertir,
sur c
...

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