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Water Content Or Moisture Content Environmental Sciences Essay

5118 words (20 pages) Essay in Environmental Sciences

5/12/16 Environmental Sciences Reference this

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Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, fruit, or wood. Water content is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 (completely dry) to the value of the materials’ porosity at saturation. It can be given on a volumetric or mass (gravimetric) basis.

The water content of a material is used in expressing the phase relationships of air, water, and solids in a given volume of material.

In fine-grained (cohesive) soils, the consistency of a given soil type depends on its water content. The water content of a soil, along with its liquid and plastic limits as determined by Test Method D4318, is used to express  its relative consistency or liquidity index.

The quality of the result produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice D3740 does not in itself ensure reliable results.

The mass of water used in the above expression is the mass of free pore water only. Hence for moisture content determination the soil samples are dried to the temperature at which only pore water is evaporated. This temperature was standardized 105 C to 110 C. Soils having gypsum are dried at 60C to 80 C.

The quantity of soil sample needed for the determination of moisture content depends on the gradation and the maximum size of particles. Following quantities are recommended.

Soil Max quantity used (gm)

Coarse gravel 1000 to 2000

Fine gravel 300 to 500

Coarse sand 200

Medium sand 50

Fine sand 25

Silt and clays 10 to 25

Moisture content affection :

Always the amount of moisture contents affects the soil strongly by different issues , and this is the dramatically classifications of the different amounts of the moisture content in the soil :

The soil is called ( brittle solid ) when its in a dry state or have a very little amount of moisture content inside the soil , and it will be hard and brittle as a result of that , though it breaks before it will deform ( hard candy ).

The soil is described as ( semi-solid ) when its have a little amount of moisture content in it , that€™s not able to cancel the solidity in the soil because of the little amount of it in the soil , and the behavior of the soil will be between the brittle and ductile state , and though it deforms permanently but with cracks ( like stiff cheese ).

The soil described also as ( plastic ) when it have a noticed amount of moisture content which have an appearance affect in the soil , when the amount of the water content is nor little neither much in the soil , and the behavior of the soil in the state will noticed directly while catching the samlple of the soil by hand , it will have a very ductile , malleable behavior , that€™s will deform without cracking ( like play-doh ).

The soil in the last case , is the ( liquid ) soil which will have for sure a big amount of moisture content inside it , it we can notice that easily by slight moving or even by the naked eye , which will be like a thick or thin viscous fluid or like a soup.

Actually always there is a limits between each state of the moisture content for the soil , and these limits called the consistency or atterberg limits of the soil , and to talk more briefly about the ( Atterberg Limits ) :

The Atterberg limits are a basic measure of the nature of a fine-grained soil. Depending on the water content of the soil, it may appear in four states: solid, semi-solid, plastic and liquid. In each state the consistency and behavior of a soil is different and thus so are its engineering properties. Thus, the boundary between each state can be defined based on a change in the soil’s behavior. The Atterberg limits can be used to distinguish between silt and clay, and it can distinguish between different types of silts and clays. These limits were created by Albert Atterberg, a Swedishchemist.[1] They were later refined by Arthur Casagrande. These distinctions in soil are used in picking the soils to build structures on top. Soils when wet retain water and expand in volume. The amount of expansion is related to the ability of the soil to take in water and its structural make up (the type of atoms present). These tests are mainly used on clayey or silty soils since these are the soils that expand and shrink due to moisture content. Clays and silts react with the water and thus change sizes and have varying shear strengths. Thus these tests are used widely in the preliminary stages of building any structure to ensure that the soil will have the correct amount of shear strength and not too much change in volume as it expands and shrinks with different moisture contents, aand here is the informations about the three atterberg limits , shrinkage , plastic and liquid limit :

Shrinkage limit

The shrinkage limit (SL) is the water content where further loss of moisture will not result in any more volume reduction.[2] The test to determine the shrinkage limit is ASTM International D4943. The shrinkage limit is much less commonly used than the liquid and plastic limits.

[edit]Plastic limit

The plastic limit is determined by rolling out a thread of the fine portion of a soil on a flat, non-porous surface. The procedure is defined in ASTM Standard D 4318.

If the soil is plastic, this thread will retain its shape down to a very narrow diameter. The sample can then be remoulded and the test repeated.

As the moisture content falls due to evaporation, the thread will begin to break apart at larger diameters. The plastic limit is defined as the moisture content where the thread breaks apart at a diameter of 3 mm (about 1/8″).

A soil is considered non-plastic if a thread cannot be rolled out down to 3mm at any moisture.

[edit]Liquid limit

The liquid limit (LL) is the water content at which a soil changes from plastic to liquid behavior. The original liquid limit test of Atterberg’s involved mixing a pat of clay in a round-bottomed porcelain bowl of 10-12cm diameter. A groove was cut through the pat of clay with a spatula, and the bowl was then struck many times against the palm of one hand.

Casagrande subsequently standardized the apparatus and the procedures to make the measurement more repeatable. Soil is placed into the metal cup portion of the device and a groove is made down its center with a standardized tool of 13.5 millimetres (0.53 in) width. The cup is repeatedly dropped 10mm onto a hard rubber base at a rate of 120 blows per minute, during which the groove closes up gradually as a result of the impact. The number of blows for the groove to close is recorded. The moisture content at which it takes 25 drops of the cup to cause the groove to close over a distance of 13.5 millimetres (0.53 in) is defined as the liquid limit. The test is normally run at several moisture contents, and the moisture content which requires 25 blows to close the groove is interpolated from the test results. The Liquid Limit test is defined by ASTM standard test method D 4318.[3] The test method also allows running the test at one moisture content where 20 to 30 blows are required to close the groove; then a correction factor is applied to obtain the liquid limit from the moisture content..[4]

The following is when you should record the N in number of blows needed to close this 1/2-inch gap:

The materials needed to do a Liquid limit test are as follows

Casagrande cup (liquid limit device)

Grooving tool

Soil pat before test

Soil pat after test

Another method for measuring the liquid limit is the fall cone test. It is based on the measurement of penetration into the soil of a standardized cone of specific mass. Although the Casagrande test is widely used across North America, the fall cone test is much more prevalent in Europe due to being less dependant on the operator in determining the Liquid Limit.

http://upload.wikimedia.org/wikipedia/commons/thumb/1/16/Atterberg_limits_02.JPG/220px-Atterberg_limits_02.JPG http://upload.wikimedia.org/wikipedia/commons/thumb/2/24/Casagrande_2.JPG/220px-Casagrande_2.JPG

[edit]Importance of Liquid Limit test

The importance of the liquid limit test is to classify soils. Different soils have varying liquid limits. Also to find the plasticity index of a soil you need to know the liquid limit and the plastic limit.

[edit]Derived limits

The values of these limits are used in a number of ways. There is also a close relationship between the limits and properties of a soil such as compressibility, permeability, and strength. This is thought to be very useful because as limit determination is relatively simple, it is more difficult to determine these other properties. Thus the Atterberg limits are not only used to identify the soil’s classification, but it allows for the use of empirical correlations for some other engineering properties.

[edit]Plasticity index

The plasticity index (PI) is a measure of the plasticity of a soil. The plasticity index is the size of the range of water contents where the soil exhibits plastic properties. The PI is the difference between the liquid limit and the plastic limit (PI = LL-PL). Soils with a high PI tend to be clay, those with a lower PI tend to be silt, and those with a PI of 0 (non-plastic) tend to have little or no silt or clay.

PI and their meanings

0 – Nonplastic

(1-5)- Slightly plastic

(5-10) – Low plasticity

(10-20)- Medium plasticity

(20-40)- High plasticity

>40 Very high plasticity

[edit]Liquidity index

The liquidity index (LI) is used for scaling the natural water content of a soil sample to the limits. It can be calculated as a ratio of difference between natural water content, plastic limit, and liquid limit: LI=(W-PL)/(LL-PL) where W is the natural water content. The effects of the water content on the strength of saturated remolded soils can be quantified by the use of the liquidity index, LI:

When the LI is 1, remolded soil is at the liquid limit and it has an undrained shear strength of about 2 kPa. When the soil is at the plastic limit, the LI is 0 and the undrained shear strength is about 200 kPa.[4][11]

[edit]Activity

The activity (A) of a soil is the PI divided by the percent of clay-sized particles (less than 2 μm) present. Different types of clays have different specific surface areas which controls how much wetting is required to move a soil from one phase to another such as across the liquid limit or the plastic limit. From the activity, one can predict the dominant clay type present in a soil sample. High activity signifies large volume change when wetted and large shrinkage when dried. Soils with high activity are very reactive chemically. Normally the activity of clay is between 0.75 and 1.25, and in this range clay is called normal. It is assumed that the plasticity index is approximately equal to the clay fraction (A = 1). When A is less than 0.75, it is considered inactive. When it is greater than 1.25, it is considered active.

After briefly explaining the the differences between the amounts of moisture content in the soil , we should explain a vey important issue , which is the methods of affection of the moisture content in the soil which is :

Strength decreases as water content increases.

􀂄 Soils swell-up when water content increases.

􀂄 Fine-grained soils at very high water content possess properties similar to liquids.

􀂄 As the water content is reduced, the volume of the soil decreases and the soils become plastic.

􀂄 If the water content is further reduced, the soil becomes semi-solid when the volume does not change.

And to talk more about the affection of the moisture aontent in the soil , this is a general affection of the moisture content in the soil at nature :

The effect of increasing soil moisture content on soil temperature, soil reflectance and soil heat storage is studied in this work. The results show that an increase in moisture content decreases the soil temperature differences between day-time and night-time, which provides protection to the plant root system against sharp and sudden changes of soil temperature. It is also found that the solar energy absorption increases as the moisture content increases, which results in a higher heat storage capacity at higher moisture content. Finally, plant growth rate and yield increased due to the modification of plant climate at higher moisture content

Water content is an important property of soils, in¯uencing soil solution chemistry and nutrient uptake by plants.Morphology and other speci®c properties of the root, nutrient concentration in the soil solution, the mobility of nutrients in the soil, and supply from solid phases, aï¬â‚¬ect nutrient uptake (Nye and Tinker, 1977; Barber, 1995). Consequently, there are consistent diï¬â‚¬erences in concen- trations of elements near the rhizoplane at a range of soil water contents (Dunham and Nye, 1976). Soil chemical properties may exert a profound in¯uence on growth and performance of plants (Grime and Curtis, 1976), and soil concentrations of several elements may be closely related to oristic composition (Tyler, 1996a). Under ®eld conditions, soil moisture ¯uctuates with temperature and rainfall. By changing soil solution chemistry, moisture ¯uctuations could regulate the availability of nutrients, and the ®eld distribution of plant species.

Water has a very different thermal conductivity than most soil particles and air (the thermal properties of the soil are determined by these three). The thermal conductivity of water is much greater than that of air, so the higher the soil moisture content the greater the thermal conductivity. The greater the soil moisture content, the more the soil thermal conductivity is like that of water. Therefore, a saturated soil has a conductivity near that of water. However, just because the soil moisture content is high, doesn’t mean that the soil will warm up faster in the Sun than a dry soil. Evaporation of the water will remove much of the Sun’s energy before the soil will have a chance to warm. Therefore, dry soils do warm up faster from sunlight and cool faster at night. This is assuming that there isn’t a vegetation cover over the soil. Most wet soils evaporate the water, keeping the soil from warming as fast during the day, and cool more slowly at night because of their greater heat capacity (because of the higher water content). 

Moisture content phase diagrame :

this is a rough photo about the general form of the phase diagram of the soil , that we use always for calculation done for moisture contents and all other issues in the soil :

http://upload.wikimedia.org/wikipedia/commons/thumb/5/54/Soil-phase-diagram.svg/300px-Soil-phase-diagram.svg.png

Weight Components:

􀂄 Weight of Solids = Ws

􀂄 Weight of Water = Ww

􀂄 Weight of Air ~ 0

Volume Components:

􀂄 Volume of Solids = Vs

􀂄 Volume of Water = Vw

􀂄 Volume of Air = Va

􀂄 Volume of Voids = Va + Vw = Vv

Weight-Volume Relationships :

􀂆 Steps to develop the weight-volume

relationship

􀂄 Separate the three phases

􀂄 The total volume of a soil

􀂄 Assuming the weight of air (Wa) to be

negligible, the total weight is then given as

V = Vs + Vv = Vs + Vw + Va

W =Ws +Ww

Objectives & Practical Applications

This is some properties that we could conclude the state of it in the soil from knowing the amount of moisture content in the soil :

€” Storability of the soil

€” Agglomeration in the case of powders

€” Microbiolgical stability

€” Flow properties, viscosity

€” Dry substance content

€” Concentration or purity

€” Commercial grade (compliance with quality agreements)

€” Nutritional value of the product

€” Legal conformity (statutory regulations governing food)

Objectives :

To learn the procedures of finding moisture content in the soil , and the variety in methods using to determine the moisture content.

To determine the quantity of moisture content in the soil by good , accurate , safe , sheep way.

To learn the differences in affection on the soil due to different amounts of moisture content in the soil

To know the performance of the soil due to different amounts of moisture contents.

To know how to use geotechnical laboratory tools, Such as the oven , balance , soil containers and all other different tools

To know the importance of this experiment in the field work and how it affects the type and method of foundations must put upon different types of structures.

Practical Applications :

Moisture content plays an important role in understanding the behavior of fine

grained soils. It is the moisture content which changes the soils from liquid state to plastic and solid

states. Its value controls the shear strength and compressibility of soils. Compaction of soils in the

field is also controlled by the quantity of water present. Densities of soils are directly influenced by

its value and are used in calculating the Stability of slopes, bearing capacity of soils-foundation

system, earth pressure behind the retaining walls and pressure due to overburden.

The knowledge of determining the moisture content is helpful in many of the laboratory tests

such as Atterberg€™s limits, shears strength compaction and consolidation.

This experiment may be performed by two different methods. Geotechnical Engineering- I

A. Oven drying method

B. Torsion balance moisture content

Actully we use the moisture content experiment mainly for getting the amount of water content inside the soil to be able to make the classification needs in the field for this soil ,and though to know how could we use this soil and where it could work and the amount of compaction needs of the soil containing a different amounts of water contents , to get the last conclusion from this important experiment , which is that the moisture content determination in the in situ in all field project is from the most important things that getting me ready to know the method of foundation that€™s need above this soil to build on it at the end , stable , strong and good structure on it .

In biological applications there can also be a distinction between physisorbed water and “free” water €” the physisorbed water being that closely associated with and relatively difficult to remove from a biological material. The method used to determine water content may affect whether water present in this form is accounted for. For a better indication of “free” and “bound” water, the water activity of a material should be considered.

Water molecules may also be present in materials closely associated with individual molecules, as “water of crystallization”, or as water molecules which are static components of protein structure.

In conclusion , Knowing the amount of moisture content of a substance helps determining if the soil is suitable for a specific use. Such like:-

To know if the soil can hold structure safely for long time safely and serviceability or not.

To be able and ready for the design of the foundation of any type of the structures.

Determining and controlling the moisture in substances is unique and necessary for many products, and the process borders between art and science , in many and variable sides of the life and nature

knowing how the Soil water regulates soil temperature by different amounts and shape of moisture content.

Soil water serves as a solvent and carrier of food nutrients for plant growth.

Tools , equipments and specimens

Equipments that we have use in the laboratory for the moisture content determination experiment :

Soil container : It€™s a container which is ceramic containers of various shapes on light wood background Stock Photo – 8282849

used to put different types of soil inside

it or a combined types with others in the

same container , and we have used it in

this experiment to put a random type of

fine-grained soil inside it and mix it with

to determine the wight of it , and actually

Soil container there are many sizes of the soil container

upon to the quantity of soil need to put

it in the container.

IMG_0212.JPG

SpatulaSpatula : it is an aluminum thin tool use to put soil by it in the soil container and for mixing the soil and water with each other in the soil container and also it€™s used for transfering soil from container and put it into heat resistance pot which is made of steel.

IMG_0209.JPG

Steel ContainerSteel Container : it is a container made of steel that have a heat resistance quality , which used to put the moist (wet) sample of soil inside it , to put the moist sample then inside the oven to dry the sample of the soil.

Digital Balance : is the instrument use to weigh the different things , that not have an enormous weights , and it used in this experiment to weigh the soil container alone once , and to weight the soil container with soil inside it then.

Digital Balance

http://www.supplierlist.com/photo_images/167132/Vacuum_Drying_Oven.jpg

Oven DryOven Dry : it is an apparatus used to heat the specimens needs to heat in the laboratories , and it was used in this experiment to dry the moist sample of soil.

moist soil sample : the wet soil > Dry soil sample : the dry soil

sample before putting in the oven sample after putting in the ovenIMG_0209.JPGIMG_0211.JPG

Moist Soil Sample

Dry soil sample

Background

Based on the literature review, the feasibility of using microwave oven to determine

moisture content of soils is well demonstrated. In addition to the GS, there is an available

international standard test method (ASTM D4643) for such determination. This method

includes requirements to control the power ratings of microwave ovens and the period of

drying procedure. Therefore, the possibility of overheating of a soil sample can be greatly

reduced. In addition, the soil sample is required to be carefully mixed after each time of

ovens heating for a certain period in order to prevent non-uniform heating of the sample.

And in this experiment we going to compute the moisture content using this test method method be determine the weight of the soil before and after the dry process by the laboratory oven dry ,and then compute by a dramatically series of calculations the amount of moisture content in that sample of soil given in the laboratory.

Procedures

According to ASTM 2216, the dry and clean container should be weighted using balance and its mass recorded.

A representative sample should be selected .

The moist representative sample should be placed in the container.

The lid should be secured in its position.

The mass of the container with the sample should be taken and recorded.

The lid should be removed and specimen should be placed in the oven.

The sample should be dried in the oven at.

The container should be removed from the oven when the sample reach a constant weight which means all the water has been evaporated.

The specimen should be weighted and recorded.

The moisture content then calculated by a series of calculations , and below in the next paragraph , all of the data and calculations is explained preefly by a list of numbers.

Work Sheet

DETERMINATION OF WATER (MOISTURE) €” CONTENT

Lab. Humidity : 57% Lab. Temperature : 20.5 0C

Moist Fine Grained Sample Of Soil

Testing Stander ASTM : D2216-92

Moisture Condition : Moisture Added

Type Of Oven : Convection Oven

Method Of Drying : Continuous Heating

Mass Of Moist Sample = 20 g

Soil Passing 4.75 mm. (No.4) Sieve = 100%

Soil Passing 37.5 mm. Sieve =100%

B3

6

OBSERVATIONS

Sample No.

Container No.

9.5

g

Mass Of Container

29.5

g

Mass Of Wet Soil + Container

28.0

g

Mass Of Dry Soil + Container

CALCULATIONS

1.5

g

Mass Of Water

18.5

g

Mass Of Dry Soil

8.1%

%

Water Content

Formulas & Calculation

Formulas:

1) Mass of water = (Mass of wet soil + container ) €” (Mass of dry soil + container)

Mw = Mcws €” Mcs

2) Mass of dry soil = (Mass of dry soil + container ) €” (Mass of container )

Ms = Mcs €” Mc

3) water content = (Mass of water)/(Mass of dry soil) *100

w = Mw / Ms *100

Calculation:

1) Mass of water = 29.5 €” 28.0

= 1.5 (g)

2) Mass of soil = 28.0 €” 9.5

= 18.5 (g)

3) Water content = 1.5/18.5 * 100

= 8.1%

Discussion

The measurement of moisture content is a lab or a procedure used to measure the amount of moisture or water that is embedded in a certain content in the soil , actually , the intended purpose for this lab or procedure once again as stated before is to measure the amount of moisture in a content. Times in construction we often need soil that must be suitable for building. In some cases the soil there and depending on where the land is located, the soil may not hold foundation of a building well. In order for us to find out if the soil is durable enough to hold the foundation of a building we might have to measure the moisture of the content. When the percent of water is found we can than choose of the soil is suitable enough for the foundation of the building. actully the most important thing we have concluded from the experiment of determining the moisture content in the soil , is to know how much amount of compaction needs for this soil under the foundation to held the structure safely. Actully all foundations (including abutment) surfaces shall be shaped one horizontal to one vertical or flatter except as otherwise specified.And after stripping (due to stripping specification), the foundation shall be loosened thoroughly by scarifying or plowing to a minimum depth of six inches. The foundation shall then be compacted to the density and moisture requirements specified for the fill Areas that are too low after stripping and shaping must be filled to base grade with compacted fill equal to that used in other parts of the project, and eventhough the moisture content determination is from the most important tests that is from the basics we need in the Geo-technichal engineering, and later on in the foundation design.

Conclusion

The result of water content we get in the experiment after quit dry of the sample in the oven dry was 8.1% which is not acceptable to be able for building over it. It€™s quite high for fine grain. This means it€™s not safe to build a structure, because the maximum allowable water content for grain is 1 %. Also this experiment is very important in Civil Engineering. Before construction it€™s very obligatory to know the water content of the soil. If the water content is very high and construction is done, that might cause damage to structure which will appear later. Actully , for each type of soil has its own capacity to keep the structure safe. For example, If the sample is coarse the maximum allowable water content is 6%. While for fine its 1% , so the last result we get from the determination of the moisture contents in this soil is that , with this high amount of moisture content we can not use this soid for the construction purposes , and if we try to do , it will cause a big proplems and damage in the building later in the future and will neve ever by safety to use it in the civil society.

Type of errors

Personal errors:-

Personal errors such as mistakes in reading from the balance , or mistakes done by wrong transferring data to the data sheet ,also the delaying of time taking out sample from oven it can cause error.

Instrumental errors:-

Errors might occur in digital balance due to the amount of accuracy of the digital balance. The reading also will change because of air condition. To eliminate such type of errors the reading should be taken several times.

Environmental errors:-

Moisture in lab and air of air condition can cause errors in readings , and though will not give us the absolute amount of moisture content , and the temperature in the laboratory affecting the sample of soil and instruments in the lab , all of these invironmental factors could give us wrong readings in the esperiment.

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