Soil compaction

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In geotechnical engineering, soil compaction is the process by which pressure applied to the soil causes densification as air moves from the pores between the grains of soil. When stress is applied that causes densification due to water (or other liquids) that move from between grains of land, then consolidation, no compaction, has occurred. Typically, compaction is the result of heavy machinery compressing the soil, but can also occur because of the passage (eg) of the animal's foot.

In soil science and agronomy, soil compaction is usually a combination of compaction and consolidation techniques, so that it can occur due to lack of water in the soil, the applied pressure is internal suction due to water evaporation as well as the passing of the animal's foot. The affected soil becomes less able to absorb rainfall, thus increasing runoff and erosion. Plants have difficulty in dense soil because mineral grains are pressed together, leaving little room for air and water, which is essential for root growth. Burrowing animals also find a hostile environment, because the dense ground is more difficult to penetrate. The soil's ability to recover from this type of compaction depends on climate, mineralogy and fauna. Soils with high swelling capacity, such as vertisol, recover quickly from compaction where humidity conditions vary (dried incantations shrink the soil, causing it to crack). But non-cracked clays can not be recovered from compacting themselves unless they entertain animals that live on the ground like earthworms - the Cecil series of land is an example.

Video Soil compaction

Under construction

Soil compaction is an important part of the construction process. It is used to support structural entities such as building foundations, highways, walkways, and retaining structures to name a few. For certain types of soils, certain properties may find it more or less desirable to work adequately for certain circumstances. In general, pre-selected soils should have sufficient strength, relatively compacted so that future settlements are insignificant, stable against volume changes due to moisture or other factors varying, durable and safe against damage, and have the right permeability.

When an area needs to be filled or backfilled, the soil is placed in a layer called the elevator. The ability of the first filler layer to be properly compacted will depend on the condition of the enclosed natural material. If the unsuitable material is left in place and backfilled, it can compress for a long time under the burden of the pile, causing cracking of settlements in filling or in any structure supported by filling. To determine whether the natural soil will support the first fill layer, an area can be proofrolled. Proofrolling consists of the use of heavy construction equipment parts (typically, heavy compaction equipment or transport equipment) to be rolled across a charging site and watch for deflections revealed. These areas will be marked by the development of rutting, pumping, or ground binding.

To ensure adequate soil compaction is achieved, the project specification will indicate the required density of the soil or the level of compaction to be achieved. This specification is generally recommended by geotechnical engineers in geotechnical engineering reports.

Soil types - that is, the grain size distribution, the grain shape of the soil, the density of the soil type, and the amount and type of clay minerals, present - have a major influence on the maximum dry weight of the unit and the optimum moisture content. It also has a major influence on how the material must be solidified in certain situations. Compaction is done using heavy equipment. In sand and gravel, the equipment usually vibrates, causing the re-orientation of soil particles to be a more dense configuration. In mud and clay, sheepsfoot rollers are often used, to create small intense shear zones, which push air out of the ground.

Adequate compaction determination is made by determining the soil density in situ and comparing it to the maximum density determined by the laboratory test. The most commonly used laboratory test is called the Proctor compaction test and there are two different methods of obtaining maximum density. They are a standard Proctor and Proctor module test; Modified proctor is more commonly used. For small dams, standard Proctor can still be a reference.

While the soil beneath the structure and sidewalks needs to be compacted, it is essential after construction to decompose the area for planting so that vegetation can grow.

Compaction method

There are several ways to achieve material compaction. Some are more suitable for soil compaction than others, while some techniques are only suitable for a particular soil or soil under certain conditions. Some are more suitable for compaction of non-soil materials such as bitumen. Generally, those who can apply large numbers of shear as well as compressive pressures, are most effective.

Available techniques can be classified as:

1. Static - great pressure is slowly applied to the ground and then released.
2. Impact - a voltage is applied by dropping large masses to the ground.
3. Vibrate - stress is applied repeatedly and quickly through mechanically actuated plates or hammers. Often combined with rotating compaction (see below).
4. Gyrating - static voltages are applied and maintained in one direction while the ground is the subject of a rotating motion about the static axis of loading. Limited to laboratory applications.
5. Rolls - heavy cylinders rolled to the ground. Commonly used in sports field. Rollers are often installed with vibrating devices to increase their effectiveness.
6. Kneading - sliding is applied in alternating movements in adjacent positions. For example, combined with turning compaction, is a 'sheepsfoot' roller used in solidification of waste in landfills.

The construction plants available to achieve compaction are highly variable and are explained elsewhere.

Test method in lab

The soil compactor is used to perform the test method which includes the laboratory compaction method used to determine the relationship between the printed water content and the weight of the soil dry unit. The soil is placed as a solidified engineering filler to a solid state to obtain satisfactory engineering properties such as shear strength, compressibility, or permeability. In addition, the foundation soil is often compacted to improve the nature of the technique. Laboratory compaction tests provide a basis for determining the percentage of solidification and molding of moisture required to achieve the required engineering properties, and to control the construction to ensure that the required compaction and water content are achieved. Test methods such as EN 13286-2, EN 13286-47, ASTM D698, ASTM D1557, AASHTO T99, AASHTO T180, AASHTO T193, BS 1377: 4 provide soil compaction testing procedures.

Maps Soil compaction

See also

• Soil compaction (agriculture)
• Compactor
• Consolidation (land)
• Homework
• Soil structure
• Aerasi
• Shear strength (ground)

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References

Source of the article : Wikipedia