1、Designation: D5126/D5126M 90 (Reapproved 2010)1Standard Guide forComparison of Field Methods for Determining HydraulicConductivity in Vadose Zone1This standard is issued under the fixed designation D5126/D5126M; the number immediately following the designation indicates theyear of original adoption
2、or, in the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEThe units statement in 1.6 and the designation were revised editorially in August 20
3、10.1. Scope1.1 This guide covers a review of the test methods fordetermining hydraulic conductivity in unsaturated soils andsediments. Test methods for determining both field-saturatedand unsaturated hydraulic conductivity are described.1.2 Measurement of hydraulic conductivity in the field isused f
4、or estimating the rate of water movement through clayliners to determine if they are a barrier to water 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 m
5、ethods are needed for measuring hydraulic conductivityranging from 1 3 102to 1 3 108cm/s, for both surface 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) hydraulicc
6、onductivity. True saturated conditions seldom occur in thevadose zone except where impermeable layers result 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 toentr
7、apped air (1).2The entrapped air prevents water frommoving in air-filled pores that, in turn, may reduce 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” co
8、ndition.1.4 Field test methods commonly used to determine field-saturated hydraulic conductivity include various double-ringinfiltrometer test methods, air-entry permeameter test methods,and borehole permeameter tests. Many empirical test methodsare used for calculating hydraulic conductivity from d
9、ataobtained with each test method. A general description of eachtest method and special characteristics 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. Di
10、rect measure-ment techniques for determining unsaturated hydraulic conduc-tivity include the instantaneous 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 w
11、ater content tomatric potential).1.6 The values stated in either SI units or inch-pound unitspresented in brackets are to be regarded separately asstandard. The values stated in each system may not be exactequivalents; therefore, each system shall be used independentlyof the other. Combining values
12、from the two systems mayresult in non-conformance with the standard.1.6.1 The gravitational system of inch-pound units is usedwhen dealing with inch-pound units. In this system, the pound(lbf) represents a unit of force (weight), while the unit for massis slugs. The rationalized slug unit is not giv
13、en, unless dynamic(F = ma) calculations are involved.1.7 This 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 o
14、f regulatory limitations prior to use.1.8 This guide offers 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 professional1This guide is under the
15、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 Aug. 1, 2010. Published September 2010. Originallyapproved in 1990. Last previous edition approved in 2004 as D512690(2004)
16、.DOI: 10.1520/D5126_D5126M-90R10E01.2The boldface numbers in parentheses refer to a list of references at the end ofthe text.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.judgment. Not all aspects of this guide may be applicable in
17、 allcircumstances. This ASTM 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 this
18、document means only that the document has been approvedthrough the ASTM consensus process.2. Referenced Documents2.1 ASTM Standards:3D653 Terminology Relating to Soil, Rock, and ContainedFluidsD2434 Test Method for Permeability of Granular Soils(Constant Head)D3385 Test Method for Infiltration Rate
19、of Soils in FieldUsing Double-Ring InfiltrometerD4643 Test Method for Determination of Water (Moisture)Content of Soil by Microwave Oven Heating3. Terminology3.1 Definitions:3.1.1 Definitions shall be in accordance with TerminologyD653.3.2 Definitions of Terms Specific to This Standard:3.2.1 Descrip
20、tions of terms shall be in accordance with Ref(2).4. Summary of Guide4.1 Test Methods for Measuring Saturated Hydraulic Con-ductivity Above the Water TableThere are several test meth-ods available for determining the field saturated hydraulicconductivity of unsaturated materials above the water tabl
21、e.Most of these methods involve measurement of the infiltrationrate of water into the soil from an infiltrometer or permeameterdevice. Infiltrometers typically measure conductivity at the soilsurface, whereas permeameters may be used to determineconductivity at different depths within the soil profi
22、le. Arepresentative list of the most commonly used equipmentincludes the following: infiltrometers (single and double-ringinfiltrometers), double-tube method, air-entry permeameter,and borehole permeameter methods (constant and multiplehead methods).4.1.1 Infiltrometer Test Method:4.1.1.1 Infiltrome
23、ter test methods measure the rate of infil-tration at the soil surface (see Test Method D2434) that isinfluenced both by saturated hydraulic conductivity 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 saturationfas
24、ter than would occur if soil were uniformly saturated. Themagnitude of the capillary effect is determined by initialmoisture content at the time of testing, the pore size, soilphysical characteristics (texture, structure), and a number ofother factors. By waiting until steady-state infiltration isre
25、ached, the capillary effects are minimized.4.1.1.2 Most infiltrometers generally employ the use of ametal cylinder placed at shallow depths into the soil, andinclude the single-ring infiltrometer, the double-ring infiltrom-eter, and the infiltration gradient method. Various adaptationsto the design
26、and implementation of these methods have beenemployed to determine the field-saturated hydraulic conduc-tivity of material within the unsaturated zone (5). The prin-ciples of operation of these methods are similar in that thesteady volumetric flux of water infiltrating into the soilenclosed within t
27、he infiltrometer ring is measured. Saturatedhydraulic conductivity is derived directly from solution ofDarcys Equation for saturated flow. Primary assumptions arethat the volume of soil being tested is field saturated and thatthe saturated hydraulic conductivity is a function of the flowrate and the
28、 applied hydraulic gradient across the soil volume.4.1.1.3 Additional assumptions common to infiltrometertests are as follows:(a) The movement of water into the soil profile is one-dimensional downward.(b) Equipment compliance effects are minimal and may bedisregarded or easily accounted for.(c) The
29、 pressure of soil gas does not offer any impedanceto the downward movement of the wetting front.(d) The wetting front is distinct and easily determined.(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 ac
30、counted 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 diameter that is drivenseveral centimetres into the soil. Water is ponded within thering above the soil surface. The upper surface of the ring isoften covered
31、to prevent evaporation. The volumetric rate ofwater added to the ring sufficient to maintain a constant headwithin the ring is measured. Alternatively, 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 ofdeclin
32、e of the water level within the ring, and the head for thelater portion of the test are used in the calculations. Infiltrationis terminated after the flow rate has approximately stabilized.The infiltrometer is removed immediately after termination ofinfiltration, and the depth to the wetting front i
33、s determinedeither visually, with a penetrometer-type probe, or by moisturecontent determination for soil samples (see Test MethodD4643).4.1.2.2 A special type of single-ring infiltrometer is theponded infiltration basin. This type of test is conducted byponding water within a generally rectangular
34、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.If 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 pre
35、sumed to be equal to thesaturated hydraulic conductivity of the soil.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM
36、website.D5126/D5126M 90 (2010)124.1.2.3 Another variant of the single-ring infiltrometer is theair-entry permeameter (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
37、are similar to the single-ringinfiltrometer, 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
38、 (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
39、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
40、 Test Method D3385 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
41、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
42、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 lay
43、er 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 assembl
44、y (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 wate
45、r 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 t
46、his 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 colle
47、ct 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 simult
48、aneously. 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 si
49、ngle 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 approximation of the wetting frontFIG. 1 Diagram of the Equipment for the Air-Entry PermeameterTechnique (from Klute, 1986)FIG. 2 Diagram of the Equipment Used for Double-Tube TestMethod (from Klute, 1986)D5126/D5126M 90 (2010)13pressure head for determination of the hydrau
