ISO INTERNATIONAL STANDARD 11276 First edition 1995-09-01 Soil quality --- Determination of pore water pressure - - Tensiometer method Qualite du sol - Détermination de la pression d'eau dans les pores - Méthodedutensiometre ISO Reference number ISO11276:1995(E) Copyright International Organization for Standardizatior Not for Resale S011276:1995(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (isO member bodies). The work of preparing Internationat 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. are Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard ISO 11276 was prepared by Technical Committee ISO/TC 190,Soil quality,Subcommittee SC 5,Physicalmethods. Annex A forms an integral part of this internationai Standard. Annexes B C, D, E and F are for information only. @ISO1995 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 Geneve 20 : Switzerland Printed in Switzerland !! Copyright International Organization for Standardization No reproduction or d without license from IHS Not for Resale ISO 11276:1995(E) INTERNATIONAL STANDARD ISO Soil quality --- Determination of pore water pressure Tensiometer method Scope NOTES 1 2 Pore water pressure is also referred to as tensiometer This International Standard specifies methods for the pressure. determination of pore water pressure in both unsatu- rated and saturated soil using tensiometers. The 3Thepore water pressurerepresents the sum of the methods are applicable for in situ pore water pressure pressuresdue tointerfacial forces acting between the measurements in the field, as well as for monitoring water,airand solid phases of the soil (matric pressure),the pore waterpressurein,forexample,plant containers part of themass of overlying material not carriedbythe soil or soil cores used in experimental procedures. skeletonandtherefore carriedbythe soilwater (overburden pressure; this pressure is often considered as part of the At normal atmospheric pressures, i.e. about 100 kPa. matric pressure) and the local air pressure within the soil (pneumatic pressure). Under most circumstances, the the application of these methods is limited to a range overburden and pneumatic pressures are zero. of pressures down to about - 85 kPa. The range is reduced at lower atmospheric pressures. Tensiometers will not function if sub-zero tempera- 2.2 matric pressure: The amount of work that must tures occur at the measurement depth. Their accuracy be done inordertotransportreversiblyand is influenced by soil and air temperature fluctuations. isothermally an infinitesimal quantity of water, ident- Tensiometer response time ranges from a few sec- ical in composition to the soil water, from a pool at the onds to several days. To obtain reliable measure- elevation and the external gas pressure of the point ments under field conditions, tensiometers require under consideration, to the soil water at the point frequent servicing. under consideration, divided by the volume of water transported. A tensiometer provides point measurements of pore different depths, several tensiometers will be 2.3 pneumatic pressure: The amount of work that necessary. In the field, replicate sets of instruments must be done in order to