Updated March 8th, 2019
Compacting loose soil is a significant part of constructing any civil engineering structures. There are many factors which affect soil compaction. I will discuss 3 most affecting factors of soil compaction in this post.
3 Most Affecting Factors of Soil Compaction
- Moisture content
- Nature and type of soil
- Compaction effort
1. Moisture content: The purpose of compaction is to minimize air voids from soil. Dry soil contains more air voids. Adding water to soil helps to compact soil and increases the dry density of soil. Adding a certain amount of water to a particular soil increases the dry density at maximum level. Adding more water to that soil will reduce the dry density of soil. The amount of water content in soil, at which soil obtains its maximum dry density, is the optimum moisture content of that soil.
2. Types and Nature of soil: There are various types of soil which are generally classified by its grain size. As per AASHTO, soil classification can be categorised into 15 groups. Naturally soil is a combination of soil types. This combination of soil types determines the best compaction method to use.
Basically we find three soil groups in nature – Granular, Cohesive and Organic.
Well graded granular soil obtain high degree of dry density. Coarse-grained soil obtain higher dry density than fine-grained soil. But, If small quantity of fines are added to coarse-grained soil, it will obtain higher dry density with same compaction effort. Adding more fines than the required for filling voids among coarse will decrease the dry density of soil.
Cohesive soils contain high quantity of air voids. This soil group requires more water to minimize air voids and therefore the optimum moisture content is high. Adding water makes this soil plastic and requires more compaction effort.
Organic soil cannot be compacted or not suitable for compaction. So, it doesn’t require any discussion.
3. Compaction effort: If compaction effort is increased, the maximum dry density of soil increases and the optimum moisture content decreases.
After a certain point soil’s dry density doesn’t increase with an increased compaction effort.
Beside the factors discussed above, there are some other factors which also affect the compaction of soil. Such as compaction method, Site condition, etc.