1、Designation: D5126 161Standard Guide forComparison of Field Methods for Determining HydraulicConductivity in Vadose Zone1This standard is issued under the fixed designation D5126; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、 year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEThe designation was editorially corrected to match the units of measurement statement in October 2016.1. Scope*1.1 T
3、his 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 for estimating th
4、e 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 methods are neede
5、d for measuring hydraulic conductivityranging from 1 102to1108cm/s, for both surface andsubsurface layers, and for both field-saturated and unsaturatedflow.1.3 For these field test methods a distinction is madebetween “saturated” (Ks) and “field-saturated” (Kfs) hydraulicconductivity. True saturated
6、 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 toentrapped air (1).2The entrappe
7、d 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” condition.1.4 Field test meth
8、ods 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 dataobtained with each test
9、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. Direct measure-ment technique
10、s 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 water content tomatric poten
11、tial).1.6 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.7 All observed and calculated values shall conform to theguidelines for significant digits and rounding established inPractice D6026.1.7.1 The method used to specify ho
12、w data are collected,calculated, or recorded in this standard is not directly related tothe accuracy to which the data can be applied in design or otheruses, or both. How one applies the results obtained using thisstandard is beyond its scope.1.8 This standard does not purport to address all of thes
13、afety 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.1.9 This guide offers an organized collection of informationor a series
14、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 ASTM standard is not intended to repre-sent or repl
15、ace 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 many1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand is the direct responsibility of Subcommittee D18.21
16、on Groundwater andVadose Zone Investigations.Current edition approved July 1, 2016. Published July 2016. Originally approvedin 1990. Last previous edition approved in 2010 as D512690(2010)1. DOI:10.1520/D5126-16E01.2The boldface numbers in parentheses refer to a list of references at the end ofthe t
17、ext.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1unique aspects. The word “Standard” in the title of thisdocument means only that the document has been approvedthroug
18、h 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) (Withdrawn 2015)4D3385 Test Method for Infiltration Rate of Soils in FieldUsing Double-Ring Infiltro
19、meterD3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD4643 Test Method for Determination of Water (Moisture)Content of Soil by Microwave Oven HeatingD6026 Practice for Using Significant Digits in G
20、eotechnicalData3. Terminology3.1 Definitions:3.1.1 For common definitions of terms in this standard, referto Terminology D653.3.2 Descriptions of other related terms can be found in Ref(3).4. Summary of Guide4.1 Test Methods for Measuring Saturated Hydraulic Con-ductivity Above the Water TableThere
21、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. Infiltrometers typically m
22、easure 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-tube method, ai
23、r-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 D2434) that isinfluenced both by saturated hydraulic conductivity as well
24、 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 of testing, the
25、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 the soil, andinc
26、lude the single-ring infiltrometer, the double-ringinfiltrometer, and the infiltration gradient method. Variousadaptations to the design and implementation of these methodshave been employed to determine the field-saturated hydraulicconductivity of material within the unsaturated zone (5). Theprinci
27、ples 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. Primary assumptions arethat
28、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 of water into the soil p
29、rofile 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 impedance tothe downward movement of the wetting front.(d) The wetting front is distinct and easily determined.(e) Dispersion
30、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 diameter that is drivensev
31、eral 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. Alternatively, if the head of
32、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 after the flow rate has app
33、roximately 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 MethodD4643).4.1.2.2 A special type of sing
34、le-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 to maintaina constant head of water within the pond is measured. If thedepth of ponding is negligi
35、ble compared to the depth of thewetting 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.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at se
36、rviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4The last approved version of this historical standard is referenced onwww.astm.org.D5126 16124.1.2.3 Another variant of the single-ring infiltrometer is theair-entry p
37、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-ringinfiltrometer, with the exception that an outer ring is includedto make sure
38、 that one-dimensional downward flow existswithin the tested horizon of the inner ring. Water that infiltratedthrough the outer ring acts as a barrier to lateral movement ofwater from the inner ring (see Fig. 2). Double-ring infiltrom-eters may be either open to the atmosphere, or most commonly,the i
39、nner 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 head tests, or from the rate of water input necessaryto maintain a stable head within the inner ring for
40、 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 Test Method D3385 for measuring infiltra-tion rates in the range of 102to 105cm/s. A modifieddouble-ri
41、ng 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 described by Boersma (9) as a means ofmeasuring the horizontal, as well as the vertical, field-saturate
42、dhydraulic 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 rate of flow in the inner cylinder and thesimultaneous rate of combined flow from in the inner and oute
43、rcylinders 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 layer of coarseprotective sand is placed in the bottom of the hole. An outertube is then placed in the hol
44、e 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 assembly (see Fig. 2) consisting ofwater supply valves and standpipes for the inner and outercylinders is inst
45、alled. 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 water supply values. After an equilibriumperiod of approximately 1 h, the hole is saturated.4.1.4.4 After s
46、aturation is achieved, the level of fall of waterin the inner standpipe, H, is recorded at given time intervals, t.H is recorded in most cases at least every 5 cm, for a totalminimum of 30 cm (Test 2). During this test, water in the outerstandpipe remains at a constant head.4.1.4.5 After the data is
47、 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, aminimum ten times as long as the time needed to collect thefirst data set.4.1.4.6 After waiting, Test 2 is performed. The levels in theouter st
48、andpipe 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 simultaneously. Both tests are thenperformed a second time or until the results of two consecuti
49、veruns 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 single 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
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