1、Designation: D5126/D5126M 16Standard 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 or, in the case of
2、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.1. Scope*1.1 This guide covers a review of the test methods fordetermining hydraulic conductivity in unsatur
3、ated 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 flux,
4、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 102to1108cm/s, for both surface andsubsur
5、face 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 conditions seldom occur in thevadose zone except where impermeable layers result in thepresen
6、ce 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 thehydraulic con
7、ductivity 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 various double-r
8、inginfiltrometer 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 affecting applica
9、bility 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 instantaneous profile (IP) t
10、est 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. No other units of measu
11、rement 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 how data are collected,calculated, or recorded in this standard is not directly related tothe ac
12、curacy 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 thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this s
13、tandard 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 of options and does not recommend a specificcourse of action. This document cannot replace edu
14、cation 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 replace the standard of care by which the adequacy ofa given professional service must be judged,
15、nor should thisdocument be applied without consideration of a projects manyunique aspects. The word “Standard” in the title of thisdocument means only that the document has been approvedthrough the ASTM consensus process.1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand
16、is the direct responsibility of Subcommittee D18.21 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/D5126-16.2The boldface numbers in parentheses
17、 refer to a list of references at the end ofthe text.*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 States12. Referenced Documents2.1 ASTM Standards:3D653 Terminology Relating
18、 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 InfiltrometerD3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of
19、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 GeotechnicalData3. Terminology3.1 Definitions:3.1.1 For common definitions of terms in this standa
20、rd, 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 are several test meth-ods available for determining the field saturated hydraulicconductivity of
21、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 measure conductivity at the soilsurface, whereas permeameters may be used to determineconductivity
22、 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, air-entry permeameter,and borehole permeameter methods (constant and multiplehead methods).4.1.1 In
23、filtrometer 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 ascapillary effects of soil (4). Capillary effect refers to the abilityof dry soil to pull or wi
24、ck 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 pore size, soilphysical characteristics (texture, structure), and a number ofother factors. By wa
25、iting 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, andinclude the single-ring infiltrometer, the double-ringinfiltrometer, and the infiltration gradient m
26、ethod. Variousadaptations to the design and implementation of these methodshave been employed to determine the field-saturated hydraulicconductivity of material within the unsaturated zone (5). Theprinciples of operation of these methods are similar in that thesteady volumetric flux of water infiltr
27、ating into the soilenclosed within the 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 i
28、s 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 profile is one-dimensional downward.(b) Equipment compliance effects are minimal and may bedisrega
29、rded 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 of clays in the surface layer of finer soils isinsignificant.(f) The soil is non-swelling, or the
30、 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 drivenseveral centimetres into the soil. Water is ponded within thering above the soil surface. The upper
31、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 waterwithin the ring is relatively large, a falling head type test maybe used wherein the flow ra
32、te, 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 approximately stabilized.The infiltrometer is removed immediately after termination ofinfiltration,
33、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 single-ring infiltrometer is theponded infiltration basin. This type of test is conducted byponding w
34、ater 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 negligible compared to the depth of thewetting front, the steady state flux of water across the soilsurf
35、ace 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 permeameter (see Fig. 1). The air-entry permeameteris discussed in 4.1.4.4.1.3 Double-Ring Infiltrometer:3For referenced ASTM stand
36、ards, 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 website.4The last approved version of this historical standard is referenced onwww.astm.org.D51
37、26/D5126M 1624.1.3.1 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 that one-dimensional downward flow existswithin the tested horizon of the inner ring. Wate
38、r 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 inner ring may be covered to prevent evaporation. For opendouble-ring infiltrometers, the fl
39、ow 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 the constanthead case; for sealed double-ring infiltrometers, the flow rate ismeasured by
40、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-ring infiltrometer test method for infiltration rates from105to 108cm/s is also being develop
41、ed.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-saturatedhydraulic conductivity of material in the vadose zone.4.1.4.2 This test method as proposed
42、 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 outercylinders is used to calculate Kfs.4.1.4.3 Aborehole is augured to the desired depth and a
43、 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 hole and sunken about 5 cm into thesoil. The outer tube is then filled with water and a smalle
44、r 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 installed. Water is then supplied to both cylinders.The standpipe for the outer cylinder is all
45、owed 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 saturation is achieved, the level of fall of waterin the inner standpipe, H, is recorded at
46、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 recorded, the inner reservoir isagain filled and the inner standpipe water level is set to
47、 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 standpipe and inner standpipe are both brought to 0. Onceagain the drop in the inner standpip
48、e 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 consecutiveruns are consistent.4.1.5 Air-Entry Permeameter:4.1.5.1 The air-entry permeameter is simi
49、lar 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 frontpressure head for determination of the hydraulic gradient, andconsequently field-saturated hydraulic conductivity.4.1.5.2 The
