DETERMINATION OF MOISTURE CONTENT OF A GIVEN SOIL SAMPLE

Determination of  Moisture content of a given soil sample.

             AIM

To determine the amount of moisture content in the grains of a soil sample.

APPARATUS

The apparatus used in the experiment includes:

•      Electronic balance 

•      Oven machine

•      Spatula

•      Non-corrodible container

•      Trimming knife

THEORY

The moisture content is also called the water content of the soil and it is defined as the ratio of weight of eater to the weight of solids in a given mass of soil.  

The moisture content of a soil is assumed to be the amount of water within the pore between the soil grains which is removable by oven drying at 105 °C – 110 °C, expressed as a percentage of the mass of dry soil.

The moisture content is generally expressed as a percentage. However, when used in the formulae giving relationship between certain quantities, it may also be expressed as a fraction.

Mathematically,

Moisture content w (%)   = M_w / M_s where

M_w is the mass of water

                   M_s  is the mass of the soil particle after drying.

Adsorbed Water

This is the layer of water on the surface of the soil particle held by powerful forces of electrical attraction and virtually in a solid state. This layer is of very small thickness, perhaps in the order of 0.005 (microns). It is pertinent to note that this layer of water cannot be removed by oven drying at 110 °C, and may therefore be considered to be part of the solid soil grain.

 PROCEDURES

After getting all the apparatus, 

•      The container was cleaned and its weight recorded.

•      The container was filled with soil sample and its new weight recorded.

•      The container filled with sample was oven-dried for about 24hours (or more) and allowed to cool.

•      The sample was re-weighed again to get the weight of the oven dried sample.

•      The experiment was repeated three times with the same soil sample for higher degree of accuracy.

DATA AND CALCULATION

The data obtained during the course of the experiments is given as given below:

Mass of the containers, m₁ = 25g, 22g and 24g

Mass of container + wet soil, m₂ = 122g, 140g, 145g.

Mass of container + dry soil (after oven drying), m₃ = 118g, 136g, 140g.

Therefore, 

Moisture content w (%)   =  [ (m₂ - m₃)  / (m₃ - m₁ )  ] * 100 

For the first experiment:

          m₁ = 25g, m₂  = 122g, m₃ = 118g.

w (%) = [ (122 - 118)  / (118 - 25)  ] * 100 

 = 4.30 %

For the second experiment:

          m₁ = 22g, m₂  = 140g, m₃ = 136g

w (%) = [ (140 - 136)  / (136 - 22)  ] * 100

                         =  3.50 %

For the third experiment:

m₁ = 24g, m₂  = 145g, m₃ = 140g w (%) = [ (145 - 140)  / (140 - 24)  ] * 100

                          =  4.3 %

So, the average moisture content for the soil sample is:

(4.3 + 3.5 + 4.3) / 3 = 4.033 %

Therefore, the average moisture content for the soil sample is 4.033 %

OBSERVATION

It was observed that the weight of the sample was reduced upon oven drying for

24hours in each of the test specimen containing the same weight of the soil sample.

PRECAUTION

Some of the precautive measures adopted during the course of the experiment were as below.

•      The sample used is true representative of the soil sample from which it was taken.

•      Each container with wet soil was weighed as soon as practicable after taking the specimen.

•      Constant mass of the soil sample was used throughout i.e. the weight of the soil sample in each container was equal.

•      It was ensured that each container harboring the sample was exposed to the same experimental condition in the oven.

•      The container was ensured cleaned, wiped and dried before filling with soil sample.

•      Parallax error was avoided when taking the readings.

ERRORS

Some of the various types of error that may undermine the outcome of the experimental result includes:

 Human Error:

•      Incorrect measurement of the sample

•      Erratic error

•      Parallax error

 Systemic Error (old age of the instruments and apparatus used)

 Instrumental Error

•      Insensitivity of the electronic balance

 Random Error 

•      Environmental air effect

•      Laboratory experimental condition

•      Effect of atmospheric water on the soil sample.

 CONCLUSION

The reduction in the weight of the soil sample upon oven drying corresponds to the weight of water lost form the grains of the soil sample. Determination of this helps in ascertaining the amount of moisture content present in the pore spaces of the grains of the soil sample in its in-situ condition.

This experiment is suffice enough to determine the amount of water content in a soil sample and can be determined as outlined in this experiment.