1、Designation: D 5126 90 (Reapproved 2004)Standard Guide forComparison of Field Methods for Determining HydraulicConductivity in Vadose Zone1This standard is issued under the fixed designation D 5126; the number immediately following the designation indicates the year oforiginal adoption or, in the ca
2、se of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers a review of the test methods fordetermining hydraulic conductivity in u
3、nsaturated soils andsediments. Test methods for determining both field-saturatedand unsaturated hydraulic conductivity are described.1.2 Measurement of hydraulic conductivity in the field isused for estimating the rate of water movement through clayliners to determine if they are a barrier to water
4、flux, forcharacterizing water movement below waste disposal sites topredict contaminant movement, and to measure infiltration anddrainage in soils and sediment for a variety of applications.Test methods are needed for measuring hydraulic conductivityranging from 1 3 102to 1 3 108cm/s, for both surfa
5、ce andsubsurface layers, and for both field-saturated and unsaturatedflow.1.3 For these field test methods a distinction must be madebetween “saturated” (Ks) and “field-saturated” (Kfs) hydraulicconductivity. True saturated conditions seldom occur in thevadose zone except where impermeable layers re
6、sult in thepresence of perched water tables. During infiltration events orin the event of a leak from a lined pond, a “field-saturated”condition develops. True saturation does not occur due toentrapped air (1).2The entrapped air prevents water frommoving in air-filled pores that, in turn, may reduce
7、 thehydraulic conductivity measured in the field by as much as afactor of two compared to conditions when trapped air is notpresent (2). Field test methods should simulate the “field-saturated” condition.1.4 Field test methods commonly used to determine field-saturated hydraulic conductivity include
8、 various double-ringinfiltrometer test methods, air-entry permeameter test methods,and borehole permeameter tests. Many empirical test methodsare used for calculating hydraulic conductivity from dataobtained with each test method. A general description of eachtest method and special characteristics
9、affecting applicability isprovided.1.5 Field test methods used to determine unsaturated hy-draulic conductivity in the field include direct measurementtechniques and various estimation methods. Direct measure-ment techniques for determining unsaturated hydraulic conduc-tivity include the instantaneo
10、us profile (IP) test method and thegypsum crust method. Estimation techniques have been devel-oped using borehole permeameter data and using data obtainedfrom desorption curves (a curve relating water content tomatric potential).1.6 The values stated in SI units are to be regarded asstandard.1.7 Thi
11、s standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.1.8 This guide offers
12、an organized collection of informationor a series of options and does not recommend a specificcourse of action. This document cannot replace education orexperience and should be used in conjunction with professionaljudgment. Not all aspects of this guide may be applicable in allcircumstances. This A
13、STM standard is not intended to repre-sent or replace the standard of care by which the adequacy ofa given professional service must be judged, nor should thisdocument be applied without consideration of a projects manyunique aspects. The word “Standard” in the title of thisdocument means only that
14、the document has been approvedthrough the ASTM consensus process.2. Referenced Documents2.1 ASTM Standards:3D 653 Terminology Relating to Soil, Rock, and ContainedFluidsD 2434 Test Method for Permeability of Granular Soils(Constant Head)D 3385 Test Method for Infiltration Rate of Soils in FieldUsing
15、 Double-Ring InfiltrometersD 4643 Test Method for Determination of Water (Moisture)1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand is the direct responsibility of Subcommittee D18.21 on Ground Water andVadose Zone Investigations.Current edition approved July 1, 2004. P
16、ublished July 2004. Originally approvedin 1990. Last previous edition approved in 1998 as D 5126 - 90 (1998)e1.2The boldface numbers in parentheses refer to a list of references at the end ofthe text.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Servic
17、e at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Content of Soil by the Microwave Oven Method3.
18、 Terminology3.1 Definitions:3.1.1 Definitions shall be in accordance with TerminologyD 653.3.2 Definitions of Terms Specific to This Standard:3.2.1 Descriptions of terms shall be in accordance with Ref(2).4. Summary of Guide4.1 Test Methods for Measuring Saturated Hydraulic Con-ductivity Above the W
19、ater TableThere are several test meth-ods available for determining the field saturated hydraulicconductivity of unsaturated materials above the water table.Most of these methods involve measurement of the infiltrationrate of water into the soil from an infiltrometer or permeameterdevice. Infiltrome
20、ters typically measure conductivity at the soilsurface, whereas permeameters may be used to determineconductivity at different depths within the soil profile. Arepresentative list of the most commonly used equipmentincludes the following: infiltrometers (single and double-ringinfiltrometers), double
21、-tube method, air-entry permeameter,and borehole permeameter methods (constant and multiplehead methods).4.1.1 Infiltrometer Test Method:4.1.1.1 Infiltrometer test methods measure the rate of infil-tration at the soil surface (see Test Method D 2434) that isinfluenced both by saturated hydraulic con
22、ductivity as well ascapillary effects of soil (4). Capillary effect refers to the abilityof dry soil to pull or wick water away from a zone of saturationfaster than would occur if soil were uniformly saturated. Themagnitude of the capillary effect is determined by initialmoisture content at the time
23、 of testing, the pore size, soilphysical characteristics (texture, structure), and a number ofother factors. By waiting until steady-state infiltration isreached, the capillary effects are minimized.4.1.1.2 Most infiltrometers generally employ the use of ametal cylinder placed at shallow depths into
24、 the soil, andinclude the single-ring infiltrometer, the double-ring infiltrom-eter, and the infiltration gradient method. Various adaptationsto the design and implementation of these methods have beenemployed to determine the field-saturated hydraulic conduc-tivity of material within the unsaturate
25、d zone (5). The prin-ciples of operation of these methods are similar in that thesteady volumetric flux of water infiltrating into the soilenclosed within the infiltrometer ring is measured. Saturatedhydraulic conductivity is derived directly from solution ofDarcys Equation for saturated flow. Prima
26、ry assumptions arethat the volume of soil being tested is field saturated and thatthe saturated hydraulic conductivity is a function of the flowrate and the applied hydraulic gradient across the soil volume.4.1.1.3 Additional assumptions common to infiltrometertests are as follows:(a) The movement o
27、f water into the soil profile is one-dimensional downward.(b) Equipment compliance effects are minimal and may bedisregarded or easily accounted for.(c) The pressure of soil gas does not offer any impedanceto the downward movement of the wetting front.(d) The wetting front is distinct and easily det
28、ermined.(e) Dispersion of clays in the surface layer of finer soils isinsignificant.(f) The soil is non-swelling, or the effects of swelling caneasily be accounted for.4.1.2 Single-Ring Infiltrometer:4.1.2.1 The single-ring infiltrometer typically consists of acylindrical ring 30 cm or larger in dia
29、meter that is drivenseveral centimetres into the soil. Water is ponded within thering above the soil surface. The upper surface of the ring isoften covered to prevent evaporation. The volumetric rate ofwater added to the ring sufficient to maintain a constant headwithin the ring is measured. Alterna
30、tively, if the head of waterwithin the ring is relatively large, a falling head type test maybe used wherein the flow rate, as measured by the rate ofdecline of the water level within the ring, and the head for thelater portion of the test are used in the calculations. Infiltrationis terminated afte
31、r the flow rate has approximately stabilized.The infiltrometer is removed immediately after termination ofinfiltration, and the depth to the wetting front is determinedeither visually, with a penetrometer-type probe, or by moisturecontent determination for soil samples (see Test MethodD 4643).4.1.2.
32、2 A special type of single-ring infiltrometer is theponded infiltration basin. This type of test is conducted byponding water within a generally rectangular basin that may beas large as several metres on a side. The flow rate required tomaintain a constant head of water within the pond is measured.I
33、f the depth of ponding is negligible compared to the depth ofthe wetting front, the steady state flux of water across the soilsurface within the basin is presumed to be equal to thesaturated hydraulic conductivity of the soil.4.1.2.3 Another variant of the single-ring infiltrometer is theair-entry p
34、ermeameter (see Fig. 1). The air-entry permeameteris discussed in 4.1.4.4.1.3 Double-Ring Infiltrometer:4.1.3.1 The underlying principles and method of operationof the double-ring infiltrometer are similar to the single-ringFIG. 1 Diagram of the Equipment for the Air-Entry PermeameterTechnique (from
35、 Klute, 1986)D 5126 90 (2004)2infiltrometer, with the exception that an outer ring is includedto ensure that one-dimensional downward flow exists withinthe tested horizon of the inner ring. Water that infiltratedthrough the outer ring acts as a barrier to lateral movement ofwater from the inner ring
36、 (see Fig. 2). Double-ring infiltrom-eters may be either open to the atmosphere, or most commonly,the inner ring may be covered to prevent evaporation. For opendouble-ring infiltrometers, the flow rate is measured directlyfrom the rate of decline of the water level within the inner ringfor falling h
37、ead tests, or from the rate of water input necessaryto maintain a stable head within the inner ring for the constanthead case; for sealed double-ring infiltrometers, the flow rate ismeasured by weighing a sealed flexible bag that is used as thesupple reservoir for the inner ring (6).4.1.3.2 Refer to
38、 Test Method D 3385 for measuring infiltra-tion rates in the range of 102to 105cm/s. A modifieddouble-ring infiltrometer test method for infiltration rates from105to 108cm/s is also being developed.4.1.4 Double-Tube Test Method:4.1.4.1 The double-tube test method proposed by Bouwer(6, 7, 8) has been
39、 described by Boersma (9) as a means ofmeasuring the horizontal, as well as the vertical, field-saturatedhydraulic conductivity of material in the vadose zone.4.1.4.2 This test method as proposed by Bouwer (6, 7, 8)utilizes two coaxial cylinders positioned in an auger hole. Thedifference between the
40、 rate of flow in the inner cylinder and thesimultaneous rate of combined flow from in the inner and outercylinders is used to calculate Kfs.4.1.4.3 Aborehole is augured to the desired depth and a holeconditioning device is used to square the bottom of the hole.The hole is then cleaned anda1to2-cm la
41、yer of coarseprotective sand is placed in the bottom of the hole. An outertube is then placed in the hole and sunken about 5 cm into thesoil. The outer tube is then filled with water and a smaller innertube is placed at the center of the outer tube. It is then driveninto the soil. A top plate assemb
42、ly (see Fig. 2) consisting ofwater supply valves and standpipes for the inner and outercylinders is installed. Water is then supplied to both cylinders.The standpipe for the outer cylinder is allowed to overflow andthe standpipe gage for the inner cylinder is set at 0 by adjustingthe appropriate wat
43、er supply values. After an equilibriumperiod of approximately 1 h, the hole is saturated.4.1.4.4 After saturation is achieved, the level of fall of waterin the inner standpipe, H, is recorded at given time intervals, t.H is recorded at least every 5 cm, for a total of at least 30 cm(Test 2). During
44、this test, water in the outer standpipe remainsat a constant head.4.1.4.5 After the data is recorded, the inner reservoir isagain filled and the inner standpipe water level is set to 0. Thesystem is allowed to re-equilibrate for a period of time at leastten times as long as the time required to coll
45、ect the first dataset.4.1.4.6 After waiting, Test 2 is performed. The levels in theouter standpipe and inner standpipe are both brought to 0. Onceagain the drop in the inner standpipe in cm, H, is recorded asa function of time, t. During the second test, however, waterlevels in both tubes drop simul
46、taneously. Both tests are thenperformed a second time or until the results of two consecutiveruns are consistent.4.1.5 Air-Entry Permeameter:4.1.5.1 The air-entry permeameter is similar to a single-ringinfiltrometer in design and operation in that the volumetric fluxof water into the soil within a s
47、ingle permeameter ring is usedto calculate field-saturated hydraulic conductivity. The primarydifferences between the two test methods are that the air-entrypermeameter typically penetrates deeper into the soil profileand measures the air-entry pressure of the soil. Air-entrypressure is used as an a
48、pproximation of the wetting frontpressure head for determination of the hydraulic gradient, andconsequently field-saturated hydraulic conductivity.4.1.5.2 The air-entry permeameter consists of a single ring,typically 30 cm in diameter, sealed at the top, that is driven intothe soil approximately 15
49、to 25 cm.Water is introduced into thepermeameter through a standpipe, to the top of which isattached a water supply reservoir. Water is allowed to infiltrateinto the soil within the permeameter ring, and the flow rate ismeasured by observing the decline of the water level within thereservoir.After a predetermined amount of water has infiltrated(based upon the estimated available storage of the soil intervalcontained within the ring), and the flow rate is relatively stable,infiltration is terminated and the wetted profile is allowed todrain. The air-entry value is the minimum p
