Chapter 3 Moisture Content

8/10/2019 Chapter 3 Moisture Content

1/9

INTRODUCTION The moisture content of soil also referred to as watercontent is an in

dicator of the amount of water present in soil. By definition, moisturecontent is theratioof the mass of waterin a sampleto the massof solids

in the sample, expressed as a percentage.In equation form,

M.x100

w = moisture content ofsoil expressed as a percentage

= mass of water in soil sample i.e., initial mass of moist soilminus mass ofoven-dried soil

M8 = mass of soil solids in sample i.e., the soil's "oven-dried

mass"

M and M8 maybe expressed in any units ofmass, but both should beexpressed in the same unit.

Itmightbe notedthat the moisturecontentcouldbe mistakenly definedas the ratioof mass ofwaterto totalmass of moistsoilrather than

tothe mass of oven-dried soil.Becausethe totalmassof moistsoil isthe

sum of the mass of water and oven-dried soil, this incorrect definition

would give a fraction in which both numerator and denominator vary

where:

3-1

Ctw*R THREE

23


2/9

24 Chapter3

but not in the same proportion according to the amount ofmoisturepresent. Such a definitionwouldbeundesirable, becausemoisturecontent would then be based on a varying quantity ofmoist mass of soilratherthan aconstantquantityof oven-dried soil.Statedanotherway,with the incorrect definition, the moisture content would not be di

rectly proportional to themass of waterpresent.With the correctdefinition given by Eq. 3-1, moisturecontent is directly proportional tothe mass of water present. This characteristic makes moisture content, asdefinedby Eq. 3-1,one ofthe most useful and important soilparameters.

APPARATUS Dryingoven with accurate temperature controland temperatureAND SUPPLIES gage

Balancewith accuracy to 0.01 g

Containers e.g.,tinor aluminummoisture cans withlids

Desiccator

Container-handling apparatus: gloves, tongs,or suitableholder formovingand handlinghot containers after drying

Miscellaneous: knives, spatulas, scoops, quartering cloth, samplesplitters, etc.

SAMPLES III 1 Samplesshallbepreservedand transportedin accordancewith

ASTM Test MethodD 4220 Groups B,C, orD

soils. Keep thesam

ples that are stored prior to testing in noncorrodible airtight con

tainers at a temperature between approximately 30 and 30C andin an area that prevents direct contact with sunlight. Disturbedsamples in jars or other containers shallbe stored in such away astoprevent orminimizemoisturecondensationon the insidesof thecontainers.

2 The water content determination should be done as soon aspracticable after sampling, especially ifpotentially corrodible con

tainers such asthin-walled steel tubes, paint cans, etc. or plastic

sample bags are used.

TEST 1 For water contents being determined in conjunction with anSPECIMEN Ill other ASTM method, the specimen mass requirement stated in

thatmethod shall be used if one is provided. If no minimum specimen mass is providedin thatmethod, then the values given belowshall apply.

2 The minimummass ofmoist material selected to berepresentative of thetotalsample shallbe inaccordancewiththe following:


3/9

Determiningthe Moisture Content of Soil ConventionalOven Method 25

Recommended Recommended

Minimum Mass of Minimum Mass of

Moist Test Spec- Moist Test Spec-

Maximum Particle imen for Water imen for WaterSize 100% Standard Sieve Content Reported Content Reported

passing Size to 0.1% to 1%

2mmorless No.10 20g 20g*

4.75mm No.4 bOg 2Og9.5mm %-in. 500 g 50 g

19.0mm 34-in. 2.5 kg 250 g37.5mm 1>-in. 10kg 1kg75.0mm 3-in. 50 kg 5kg

NOTE_*To be representativenot less than 20 g shall be used.

2.1 The minimum mass used may have to beincreased to obtainthe needed significant digits for the mass ofwaterwhen reporting

water contents to the nearest0.1%.

3 Usinga test specimen smaller than the minimum indicated in

2 requiresdiscretion,though it m ay be adequate for the purposes

of the test. Any specimen used not meeting these requirements

shall benoted onthetest data forms or test data sheets.

4 When working with a small less than 200 g specimen containinga relativelylarge gravel particle,it is appropriate not to in

clude this particle in the test specimen. However, any discarded

materialshall be described and noted onthe test dataformsor test

datasheets.

5 For those samples consisting entirely of intact rock, the mini

mum specimenmass shallbe 500 g. Representativeportions of thesample may be broken into smaller particles, depending on thesample's size, the container, and balance being used, and to facili

tate drying to constant mass, see Section 4 under"Procedure."

TEST SPECIMEN 1 When the test specimen is a portion ofa larger amount of ma-SELECTION III terial, the specimenmust beselectedtoberepresentativeof thewa

terconditionof theentireamount of material. Themanner inwhich

the test specimen is selected depends on the purpose and applica

tion ofthe test, type of material being tested, the water condition,

andthe typeof samplefrom another test,bag,block,and the likes.

2 For disturbed samples, such as trimmings, bag samples, and

the like, obtain the test specimen by one of the following methods

listed in order ofpreference:

2.1 Ifthe material is such that it can be manipulated and handled withoutsignificant moisture loss and segregation,the mater

ialshould bemixedthoroughlyand then selectarepresentative por

tion using a scoop of a size that no more than a few scoopfuls are

requiredto obtainthe propersize of specimendefinedbyNo. 2 un

derthe Section "Test Specimen."


4/9

26 ChapterS

2.2 If the material is such that it cannot be thoroughly mixedand/or split, form a stockpile of the material, mixing as much aspossible.Take at least fiveportionsof material at randomlocationsusing a sampling tube, shovel, scoop, trowel, or similar device appropriate to the maximum particle size present in the material.Combine all the portions for the test specimen.

2.3 Ifthe material or conditions are such that a stockpile cannotbeformed,take as manyportionsofthe materialas practical usingrandom locations that will best represent the moisture condition.Combine all the portions for the test specimen.

3 Intactsamples,suchas block,tube,splitbarrel,andthe like,obtain the test specimen by one of the following methods dependingon the purpose and potentialuse ofthe sample.

3.1 Usinga knife,wire saw, orothersharpcuttingdevice,trimtheoutsideportion ofthe sample a sufficient distanceto seeifthe material is layered and to remove material that appears more dry or

more wet than the main portion of the sample. Ifthe existence oflayeringis questionable, slice the sample in half. Ifthe material islayered,see No. 3.3.

3.2 If thematerialis not layered,obtain the specimen meetingthemass requirementsin No. 2 underthe Section"TestSpecimen" by:1 taking all or one-halfof the intervalbeing tested; 2 trimminga representative slice from the interval being tested; or 3 trimming the exposed surface of one-half or from the interval beingtested.

Note 1-Migrationofmoisturein some cohesionless soils may

requirethatthe full sectionbe sampled.

3.3 Ifa layered material or more than one material type is encountered, select an average specimen, or individual specimens, orboth. Specimens must be properlyidentified as to location or whatthey represent and appropriate remarks entered on the test dataforms or test data sheets.

PROCEDURE Determinationof moisture contentofsoil is actuallyquitesimple. As indicatedbyEq. 3-1, it is necessaryonlyto determinethe1 massofwa

ter in thesoil sampleand 2 massof soil solids in the samesample.Thisis easily done by determiningthe mass ofthe moist soil sample, dryingthe sample to removemoisture, and then measuringthe mass of the remaining oven-driedsample.The mass ofthe remainingoven-dried sample is,of course,the mass ofsoil solids in the sample. The differencebetweenthat mass and the mass of the original moist sample is the massofwaterin the original sample. Substituting thesevalues into Eq. 3-1will give the desired moisturecontentof the soil.


5/9


6/9


7/9


8/9


9/9

Sample No.

SoilsTesting LaboratoryMoIstureContent Determination

Boring No.

___________ ______

Depth

Description of Sample

Testedby

Project No.

Location -

Date

Determination Na: 1 2 3

Container can no.

Mass of container + wet specimen, M09g

Mass of container + oven-dried specimen, Mg

Mass of container, M0 g

Mass of water, Mg

Mass of solid particles, Mg

Moisture content, w%

31

Chapter 3 Moisture Content

Documents

Transcript of Chapter 3 Moisture Content