Question

a. Equipment play important role in construction project. Appraise five equipment uses for compaction in civil engineering field. (EV5 Marks)

b. As a student you are given a project to manage. Explain Factors Influencing compaction on soil properties (AN6 Marks)

c. Moisture content is one of the lubricant use in compaction of road soil works. Formulate Moisture content test (CR7 marks)

Answer 1

A.

There are different types of rollers and other soil compaction equipments available. Use of these compacting machines depends on soil types and moisture conditions.

1.Rammers:

Rammers are used for compacting small areas by providing impact load to the soil. This equipment is light and can be hand or machine operated. The base size of rammers can be 15cm x 15cm or 20cm x 20cm or more.

2. Vibrating plate compactors :

These are used for compaction of coarse soils with 4 to 8% fines. These equipments are used for small areas. The usual weights of these machines vary from 100 kg to 2 tonne with plate areas between 0.16 m2 and 1.6 m2.

3.Vibro Tampers:

Vibro tampers is used for compaction of small areas in confined space. This machine is suitable for compaction of all types of soil by vibrations set up in a base plate through a spring activated by an engine driven reciprocating mechanism. They are usually manually guided and weigh between 50 and 100 kg (100 to 220 lbs).

4.

Smooth Wheeled Rollers:

Smooth wheeled rollers are of two types:

• Static smooth wheeled rollers
• Vibrating smooth wheeled rollers

The most suitable soils for these roller type are well graded sand, gravel, crushed rock, asphalt etc. where crushing is required. These are used on soils which does not require great pressure for compaction. These rollers are generally used for finishing the upper surface of the soil. These roller are not used for compaction of uniform sands.

5.Pneumatic Tyred Rollers:

Pneumatic tyred rollers are also called as rubber tyred rollers. These rollers are used for compaction of coarse grained soils with some fines. These rollers are least suitable for uniform coarse soils and rocks. Generally pneumatic tyred rollers are used in pavement subgrade works both earthwork and bituminous works.

B.

Following the different factors affecting compaction of soil:

• Water content
• Amount of compaction
• Types of soil
• Methods of soil compaction
• Contact pressure
• Speed of rolling

Effect of Water Content on Compaction of Soil

At low water content, the soil is stiff and offers more resistance to compaction. As the water content is increased, the soil particles get lubricated. The soil mass becomes more workable and the particles have closer packing.The dry density of the soil increases with an increase in the water content till the optimum water content in reached. At that stage, the air voids attain approximately a constant volume. With further increase in water content, the air voids do not decrease, but the total voids (air plus water) increase and the dry density decreases.Thus the higher dry density is achieved upto the optimum water content due to forcing air voids out from the soil voids. After the optimum water content is reached, it becomes more difficult to force air out and to further reduce the air voids.

Amount of Compaction

The compaction of soil increases with the increase in amount of compactive effort. With increase in compactive effort, the optimum water content required for compaction also decreases. At a water content less than the optimum, the effect of increased compaction is more predominant.At a water content more than the optimum, the volume of air voids become almost constant and the effect of increased compaction on soil is not significant.

Types of soil

The soil type influences the compaction of that soil to a great extent. The coarse grained soils can be compacted to higher dry density than the fine grained soils. The maximum dry density decreases if the quantity of fines is increased to an amount more than that required to fill voids in the coarse grained soils. Hence it’s safe to say a well graded soil obtains a much higher dry density than a poorly graded soil.Cohesive soils such as heavy clays, clays & silts provide higher resistance to compaction as they attain lower maximum dry density. Cohesionless soils such as sandy soils and coarse grained or gravelly soils are susceptible for easy compaction.

Method of soil compaction

The dry density achieved depends not only upon the amount of compactive effort but also on the method of compaction. For the same amount of compactive effort, the dry density will depend upon whether the method of compaction utilizes kneading action, dynamic action or static action.

For example, in Harvard Miniature compaction test, the soil is compacted by the kneading action, and therefore, the compaction curve obtained is different from that obtained from the other conventional tests in which an equal compactive effort is applied.

Contact Pressure

Contact pressure is the pressure between thesoil and wheels of the equipment used for compaction. This pressure depends on the weight of the roller wheel and the contact area. A higher contact pressure increases the dry density and lowers the optimum moisture content.

Speed of Rolling

The speed of rolling is the speed with which the soil is compacted is a significant factor. There are two important things to be considered. The first thing is, the higher the speed of rolling, the more length of embankment can be compacted in a day. Secondly, at higher speed of rolling there is likely a chance of insufficient time required for the deformations to take place and hence more passes may be required to achieve the desired compaction.

C.

Test Procedure of Oven Dry Method

The test procedure of Oven Dry method to find the moisture content of soil consists following steps.

• In first step, clean and dry the containers and weigh them and note down the mass of each container (M1). Also note down the number of each container along with its weight.
• Collect the soil sample from field. Remove the top layer of soil and collect the wet soil from bottom layers.
• Fill the containers with required quantity of soil sample and weigh the each container and note down its mass (M2).
• Place the containers in hot air oven, arrange temperature to 110o ± 5o C and allow them to dry for 24 hours.
• After 24 hours turn off the oven and take out the containers using tongs.
• Cool down the containers in desiccator for one hour.
• After that weigh containers and note down the mass (m3) of each container.

Observations and Calculations of Oven Dry Method

The data collected during the test is noted in below data sheet. From this data the water content of given soil sample is calculated by the below shown formula

W=(M2-M3/M3-M1)×100

Where M1= Mass of empty container with lid,

M2= Mass of the container with wet soil and lid,

M3= Mass of the container with dry soil and lid.

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