1、BRITISH STANDARD ICS 13.080.20 BS EN ISO 11276:2014 Soil quality Determination of pore water pressure Tensiometer methodNational foreword This British Standard is the UK implementation of EN ISO 11276:2014. It is identical to ISO 11276:1995. It supersedes BS 7755-5.1:1996 (dual numbered as ISO 11276
2、:1995), which is withdrawn. The UK participation in its preparation was entrusted to Technical Committee EH/4, Soil quality. A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of
3、 a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal obligations. BS EN ISO 11276:2014 This British Standard, having been prepared under the direction of the Health and Environment Sector Board, was published under the a
4、uthority of the Standards Board and comes into effect on 15 April 1996 Amendments/corrigenda issued since publication Date Comments 31 May 2014 This corrigendum renumbers BS 7755-5.1:1996 (dual numbered as ISO 11276:1995) as BS EN ISO 11276:2014 ISBN 978 0 580 82149 3 The British Standards Instituti
5、on 2014. Published by BSI Standards Limited 2014 EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 11276 March 2014 ICS 13.080.20 English Version Soil quality - Determination of pore water pressure - Tensiometer method (ISO 11276:1995) Qualit du sol - Dtermination de la pression deau dans les
6、 pores - Mthode du tensiomtre (ISO 11276:1995) Bodenbeschaffenheit - Bestimmung des Porenwasserdrucks - Tensiometerverfahren (ISO 11276:1995) This European Standard was approved by CEN on 13 March 2014. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the con
7、ditions 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 exis
8、ts 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 sta
9、ndards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, S
10、lovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels 2014 CEN All rights of exploitation in any form and by any means reser
11、ved worldwide for CEN national Members. Ref. No. EN ISO 11276:2014 EForeword The text of ISO 11276:1995 has been prepared by Technical Committee ISO/TC 190 “Soil quality” of the International Organization for Standardization (ISO) and has been taken over as EN ISO 11276:2014 by Technical Committee C
12、EN/TC 345 “Characterization of soils” 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 September 2014, and conflicting national standards shall be withdrawn
13、 at the latest by September 2014. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights. According to the CEN-CENELEC Internal Regulations, t
14、he national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latv
15、ia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. Endorsement notice The text of ISO 11276:1995 has been approved by CEN as EN ISO 11276:2014 without any modification. 2 BS EN ISO 11276:201
16、4 EN ISO 11276:2014 (E) BSI 03-2000 i Contents Page 1 Scope 1 2 Definitions 1 3 Principle 1 4 Apparatus 2 5 Procedure 3 6 Expression of results 5 7 Test report 5 Annex A (normative) Construction and use of mercury manometers 7 Annex B (informative) Tensiometer materials and construction 10 Annex C (
17、informative) Examples of pressure sensors other than mercury manometers 11 Annex D (informative) Field installation of tensiometers 12 Annex E (informative) Relation of pore water pressure and hydraulic pressure, and calculation from tensiometer measurements 14 Annex F (informative) Bibliography 16
18、Figure 1 The main elements of tensiometers incorporated into avarietyofdesigns intended for field and laboratory use 4 Figure 2 Components of the pressure measured by a sensor attachedtoatensiometer 6 Figure A.1 Mercury manometer system for use with tensiometers 8 Figure A.2 Diagram of the pressure
19、components measured by a mercury-manometer type tensiometer 9 Figure B.1 Alternative air trap and connecting tube arrangements 11 Figure D.1 Tensiometer installed at depth from the side of a pit 13 Figure D.2 Tensiometer installation methods 14 Table 1 Conversions between soil water potential and it
20、s pressure and head equivalents 2 BS EN ISO 11276:2014 ISO 11276:1995This page deliberately set blank BSI 03-2000 1 1 Scope This International Standard specifies methods for the determination of pore water pressure in both unsaturated and saturated soil using tensiometers. The methods are applicable
21、 for in situ pore water pressure measurements in the field, as well as for monitoring pore water pressure in, for example, plant containers or soil cores used in experimental procedures. At normal atmospheric pressures, i.e.about100kPa, the application of these methods is limited to a range of press
22、ures down to about85kPa. The range is reduced at lower atmospheric pressures. Tensiometers will not function if sub-zero temperatures occur at the measurement depth. Their accuracy is influenced by soil and air temperature fluctuations. Tensiometer response time ranges from a few seconds to several
23、days. To obtain reliable measurements under field conditions, tensiometers require frequent servicing. A tensiometer provides point measurements of pore water pressure. To measure pore water pressure at different depths, several tensiometers will be necessary. In the field, replicate sets of instrum
24、ents will be required if the spatial variability of the soil is to be allowed for. 2 Definitions For the purposes of this International Standard, the following definitions apply. NOTE 1Additional definitions are given in E.2, for information only. 2.1 pore water pressure the sum of matric and pneuma
25、tic pressures NOTE 2Pore water pressure is also referred to as tensiometer pressure. NOTE 3The pore water pressure represents the sum of the pressures due to interfacial forces acting between the water, air and solid phases of the soil (matric pressure), the part of the mass of overlying material no
26、t carried by the soil skeleton and therefore carried by the soil water (overburden pressure; this pressure is often considered as part of the matric pressure) and the local air pressure within the soil (pneumatic pressure). Under most circumstances, the overburden and pneumatic pressures are zero. 2
27、.2 matric pressure the 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
28、the point under consideration, divided by the volume of water transported 2.3 pneumatic pressure the 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 atmospheric pressure
29、and at the elevation of the point under consideration, to a similar pool at an external gas pressure of the point under consideration, divided by the volume of water transported NOTE 4Soil water pressure can be considered as a pressure equivalent of soil water potential. The same applies to the soil
30、 water head, the head equivalent of soil water potential. The relationship between these is ? w = p hg w In this International Standard pressure equivalents and soil water potentials are used. The corresponding unit of measurement is the pascal (Pa).Table 1 provides conversions between soil water po
31、tential and its pressure and head equivalents. 3 Principle A tensiometer comprises a porous cup that ispermeable to water connected to a pressure-measuring device. The pores of the wall of the cup are small enough to prevent air passing through when it is wet. The porous cup is filled with water. Wh
32、en the cup is placed in the soil, water within the tensiometer flows through the porous wall to the soil, or soil water flows into the tensiometer, until the pressure of the water on both sides of the porous wall is equal. When equilibrium has been reached, the measured pressure of the water inside
33、the tensiometer, after correction for the difference in height between the pressure sensor and the porous cup equals the pore water pressure of the soil water at the position of the porous cup. where ? is the soil water potential, in joules per kilogram on a mass basis; p is the pressure equivalent
34、of soil water potential, injoules per cubic metre on a volume basis(1j/m 3 =1N/m 2 =1Pa); h is the head equivalent of soil water potential, in joules per newton on a force basis(1J/N=1m); w is the density of water, in kilograms per cubic metre; g is the acceleration due to gravity, in metres per sec
35、ond squared. BS EN ISO 11276:2014 ISO 11276:19952 BSI 03-2000 4 Apparatus 4.1 Tensiometer, usually consisting of a porous cup, a connecting tube and/or a body tube, a pressure sensor and a mechanism for expelling any air which accumulates within the tensiometer. The details of the design depend prim
36、arily on whether the instrument is intended for field or indoor use and the type of pressure sensor employed; examples are shown inFigure 1.Annex B provides information on materials for the construction of tensiometers and on their construction. 4.1.1 Porous cup, made of a porous material of air-ent
37、ry value (i.e.the pressure required to force air through the water-saturated cup) larger in magnitude than the lowest pore water pressure to be measured and the known hydraulic conductivity. The material shall be rigid and not subject to degradation in soil. Usually unglazed ceramic is used; alterna
38、tives are described inAnnex B. 4.1.2 Connecting and body tubes, made from appropriate materials of low permeability to water and gas and connected by leakproof joints. Rigid or semi-rigid tubing shall be used to connect the tensiometer to the pressure sensor (seeAnnex B). The function of the connect
39、ing tube may, in part or totally, be served by the body tube. The body tube usually fills the hole remaining above or behind the tensiometer cup after inserting it into the soil. It is a rigid tube with the same outside diameter as the porous cup. In many designs, it is filled with water, but in oth
40、ers it forms a casing for smaller tubes connected to the porous cup and/or cables attached to a pressure transducer located behind the cup. Table 1 Conversions between soil water potential and its pressure and head equivalents 4.1.3 Pressure sensors. Several forms are used in tensiometers, the most
41、common being mercury manometers, Bourdon gauges and electrical pressure transducers. The use of other types of manometer is permissible. The accuracy of the pressure sensor determines how accurately the pressure of the water within the tensiometer can be measured. Annex A details the construction an
42、d use of mercury manometers for use with tensiometers. The other pressure sensors are described inAnnex C. The accuracy of Bourdon gauge and pressure transducer tensiometers shall be verified before installation and at least annually thereafter. NOTE 5The accuracy of instruments used in the field ma
43、y be tested with a mercury manometer reference. The complete tensiometer assembly can be tested in the field by inserting a “T” piece into the connecting tube. When required, another connecting tube is attached to it for connection to a mercury manometer. Should greater accuracy be required for labo
44、ratory purposes, specialized testing equipment will be necessary. 4.2 Tensiometer construction Details of materials for constructing tensiometers and of their construction are given in Annex B. Since the interior of a tensiometer installed in unsaturated soil is under a partial vacuum, it is essenti
45、al that all possible leakage points are made as secure as possible. The number of joints in the system shall be kept to the minimum possible. Adhesive joints shall be made so that the void space between components is filled completely. Joints relying on a tight fit of two materials, for example stop
46、pers, shall be correctly sized, with as large an area of contact as possible. The system is used in a damp environment. Hence all materials shall be chosen to resist moisture. Thisapplies particularly to adhesives, some kinds of which may soften or swell (leading to failure of cemented parts) in dam
47、p conditions. If a tensiometer assembly of new design or of untried materials is to be used, it shall be tested for leaks under pressure and/or under vacuum before installation. This procedure is recommended for all installations. Parameter to be converted Pressure equivalent (Pa) Head equivalent (m
48、) Potential (J/kg) Pressure equivalent (Pa) Head equivalent(m) Potential (J/kg) 1 9807 10 3 0,1020 10 3 1 0,1020 10 3 9,807 1 NOTE 1To convert from the potential or its equivalent in the first vertical to another equivalent or potential, multiply by the factor given, for example: a potential of1J/kg
49、 has a pressure equivalent of10 3 Pa and a head equivalent of0,1020m. NOTE 2Acceleration due to gravity=9,807m/s 2 Density of water=1000kg/m 3 BS EN ISO 11276:2014 ISO 11276:1995 BSI 03-2000 3 5 Procedure 5.1 Installation of tensiometers Tensiometers may be installed vertically or horizontally, whichever is most suitable for the required purpose. Install each tensiometer so that the centre of the porous cup is at the depth at which measurement is required. Ensure minimal disturbance to the soil that will surround the tensiometer, both at
