What is Soil Compaction?
By reducing the void space between soil particles, soil compaction is the practice of applying mechanical compaction force to densify soil. When particles are compressed to close the distance between them, compaction takes place. Because there are so few spaces left in highly compacted soils, the soil has a higher unit weight. Maximum density is attained at an OMC, or optimum moisture content.
What Factors Affect Soil Compaction?
Type of Soil
When it comes to compaction, different soil types react differently. Particle size and, in some soil categories, critical water content values or Atterberg limits are used to classify soils. In construction applications, well-graded granular soils with a variety of particle types are preferred because they can be easily compacted, eliminating voids by interlocking the particles and preventing moisture absorption, which enables the soil to support heavier loads because it is a very dense soil. Due to the narrow range of particle sizes and lack of shear strength, which is not related to the non-interlocking particles because of their similar sizes, poorly graded soils are less suitable for construction purposes.
Moisture Content
In soil compaction, water content is a key factor. Only when the water content is at the ideal level can the maximum dry density be reached. The optimum moisture content, or OMC, is at this point. In a lab, maximum dry density and the ideal moisture content are identified, and these values are then used as targets for on-site operations.
Speed of Rolling
There is a dichotomy to take into account when talking about soil compaction speed. More space can be compacted with faster compaction rates. However, if compaction is carried out too quickly, the required deformations might not occur in enough time. In this situation, more passes would be necessary to finish the compaction process.
Contact Pressure
Realizing the contact pressure between the soil and the compaction machinery is also crucial. The total weight of the compaction equipment and the area of soil it contacts both have an impact on contact pressure. More compaction is attained the higher the contact pressure.
Methods Used to Compact Soil?
There are numerous techniques for compacting soil. All techniques involve the manipulation of the soil in addition to a static and/or dynamic force. Static force compacts soil physically and continuously by applying weight pressure. Soil can be compacted at greater depths through manipulation, such as kneading or shearing the soil in alternate directions. A vibrating mechanism can be used to apply dynamic force in addition to pressure and manipulation. Vibratory compaction techniques apply force in alternating directions by using different amplitudes (the amount of movement on an axis) and frequencies (the speed of the movement), typically by using a rotating weight to deliver quick blows to the surface. This causes the soil’s particles to be rearranged, causing compaction throughout the soil, not just in the topmost layers. Impact compaction, which involves using a falling weight, is another dynamic technique for compacting soil. Additionally, this technique can compact soil at greater depths.
Advantages Over Construction
The increased strength qualities of compacted soil also improve its bearing capacity, allowing for greater, heavier loads such as buildings, dams, or other similar structures to be built on top of the compacted soil. Additional benefits of soil compaction include increased soil structure stability, reduced degradation (i.e. erosion), and increased soil permeability (water passage).
