Determining the Moisture Content of a Sample Soil

A soil is an aggregate of soil particles having a porous structure. The pores may have water or air. The pores are also known as voids. If voids carefully filled with water. The soil is called saturated soil and if voids have only air the soil is called dry.

The moisture content of a soil is assumed to be the amount of water present in within the pore between the soil grains which is removed by oven drying or other means at 105 degree – 110 degree, expressed as the percentage of mass of dry soil.

Moisture content is also defined as the ratio of the mass/weight of water to the mass/weight of water to the mass/weight of soil solids.

Moisture content determined by;

w(%) = (Mb-Mc)/(Mc-Ma) X 100

Where,
Ma = mass of empty container
Mb = mass of container + wet soil
Mc = mass of container + air dried soil

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 degree to 110 degree. Soils having gypsum are dried at 60 degree to 80 degree. The quantity of soil sample needed for the determination of moisture content in the laboratory are open air, oven-drying, pycno-meter, infrared lamp with torsion balance moisture meter.

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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. Density 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. The approximate methods are alcohol burning method and calcium carbide method. In this experiment we will be using the open air method.

 

PROCEDURES

To carry out the specific gravity operation, the followings are the procedures used:

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• The containers and lid are thoroughly clean, then measure afterwards(Ma).

• The mass of the soil sample to be use is weigh and record as (Mb).

• The containers are fill with sample of soil and weigh and record as Mb.

• The containers is air – dry for 24 hours.

• The containers is re-weigh after air drying and record as Mc.

• Lastly, calculate the percentage.

 

DATA AND CALCULATION

Moisture content determined by;

w(%) = (Mb-Mc)/(Mc-Ma) X 100

Where,
Ma = mass of empty container
Mb = mass of container + wet soil
Mc = mass of container + air dried soil

 

PRECAUTIONS

• Ensure accurate measurement of the soil sample.

• Ensure that all the apparatus being use are clean and free from dirt before use.

• Utmost care should be taken in handling the apparatus.

 

APPARATUS

The following are the apparatus use determining the moisture content of soil.

• Chattaway spatula 150mm X 3mm

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• Analytical balance reading ( to 0.001g)

• Pan

 

POSSIBLE ERRORS

Natural Error: This include uneven distribution of air and humidity in the practical lab.

Systematic Error: This can occur due to old age and inefficiency of the apparatus being used

Human Error: This may be in form of parallax or as a result of the inexperience of the group members.

 

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Determining the Moisture Content of a Sample Soil

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