The aim of soil stability test is to determine the effect of cement on OMC & MDD of the given soil sample.
Different soil samples exist with various dry and wet densities. After compaction, the voids are reduced and the density is increased. There exist certain soil type that do not meet up the required maximum density after compaction. The maximum density of such soils can be increased through a process called stabilization.
Stabilization involves the addition of certain additive materials to soils to improve its cohesion and therefore increase its maximum density after compaction. Stabilization can be done with
• Soil – cement stabilization
Types I and IA, normal and air entering cements, are most commonly used. All soils can be stabilized with Portland cement, provided sufficient quantity is added. Some soils with a high organic content do not react well with cement and hardening may be delayed. As clay content increases, soils become more difficult to pulverize and work, and larger quantities of cement must be added to harden them. The thickness of a cement-stabilizes base depends upon the traffic loads and volumes and the stability of the subgrade. Thicknesses greater than 7 inches are built in more than one lift. The thickness of sub-base or subgrade stabilization depends upon the nature of the soils and the conditions of the job.
• Soil – lime stabilization
Hydrated lime (calcium hydroxide) is mainly used. There are two basic types of lime: High calcium and High magnesium. Their soil-stabilizing ability is roughly equal. Quicklime is occasionally used to stabilize heavy clays. Quicklime is a strong caustic and requires the use of goggles and protective clothing. Use of a non-dusting granulated product reduces the danger slightly. Principal advantage is a saving in shipping costs: hydrated lime is about one-fourth chemically combined water; quicklime is free from water.
To carry out the stabilization test, the following are the procedures used:
1. Obtain the soil sample and weighed out 3kg of it.
2. The mould without its collar is then weigh to the nearest 1g.
3. 8% of the soil sample (240g) is remove and substitute with cement.
4. Pour the soil sample in the mixing pan and sprinkled 4% (120ml) of water on it and then mix it thoroughly with the hand trowel provided.
5. Part of the thoroughly mixed sand is pour in the compaction mould in three different layers with each of the layers receiving 25 blows of the compaction rammer.
6. The mould together with the wet soil sample is then detach from the base and weigh.
7. Scoop a little quantity off the wet soil into one of the moisture cans and then turn the mould upside down to scoop from the bottom part.
8. The moisture cans with soil sample are weighed and kept safely apart.
9. Pour the remaining part of the sand in the mould into the mixing pan and add a further 60ml of water in the soil.
10. This entire process is then repeated till the soil attains full compaction and further addition of water led to a decrease in the compactivity of the soil sample.
The following are the apparatus used during the execution of the practical:
• Compaction mould
• Compaction hammer
• Content cans
• An oven
• Hand trowel
1. 2760g of soil sample
2. 240g (8%) of cement
3. Clean water
It was observed during the course of the experiment that:
• As the moisture content increase, the dry density and bulk density increase up to a point i.e. optimum moisture content before they started reducing in magnitude.
• Increase in moisture content; increase in the level of compaction to a point before the excess water starts to push the soil particles apart and makes it difficult to compact.
• The volume of soil sample started decreasing after the maximum dry density has been reached.
• You should observe that the OMC of using lime is greater than that of cement while the MOD of using cement is greater than that of lime.
1. Ensure that the weighed balance is working perfectly before commencing the experiment.
2. Ensure that the soil is properly mixed after addition of water to avoid uneven absorption of water.
3. The soil should be thoroughly ram in 3 layers to remove air voids.
4. Ensure that the rammer is drop from a control height of 300mm for each of the 25 blows.
• 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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