Why does soil compact

Compaction increases the shear strength of soils by adding friction from the interlocking of particles. Future settlement of soils is reduced by increasing the stiffness and eliminating voids creating a densified soil.

The removal of voids reduces the chance of the soil settling or shrinking or expanding and it decreases water seepage that would lead to deleterious shrinking and swelling soil properties. Maximum dry density, along with optimum moisture content, is determined in the laboratory and provides the target for field compaction. The compactive threshold will be provided by the designing engineer and will be based on the bearing capacity required for the final load to be structurally stable.

There are two basic configurations for What is Soil Remediation? Soil remediation is the application of proven technologies to mitigate What is the Objective of Soil Compaction? Get started now. Types of Soil Compaction Equipment Compaction equipment has been used in construction since the early 20th century. Smooth rollers use static pressure, sometimes in conjunction with vibration and impact, to compact soil. Smooth rollers are not the only type of compactor utilized, but more than likely used in the final compaction step to provide a smooth surface for construction.

Padfoot and Tamping foot rollers use manipulative force to break the natural bonds between particles for better compaction, especially in cohesive soils. They have tapered feet so they do not fluff the soil decreasing the ability of soil to absorb additional water content should it rain. On small to medium soil compaction jobs or mainly gravel soils, pneumatic rollers use staggered rubber tires with varying air pressure where the surface of bladed granular soils needs to be sealed.

These units typically have ballast systems that allow weight to be added or decreased as needed to meet compaction goals. Tire pressure can also be altered to help meet compaction goals. Macropores are large enough to be emptied of water by gravity; a condition usually found a day or two after heavy winter rain 'field capacity'.

They play a role in transmitting air and water through the soil. Macropores include shrinkage cracks, burrows made by soil macrofauna worms, ants and termites and old root channels. Mesopores are small enough to retain water against the pull of gravity at field capacity, to be available to plants.

As soils absorb water and they drain and have water extracted from them, the forces developed between soil particles in the menisci skins which separate water from air can be large enough to draw soil particles together.

You can see the same forces at work when you put a dry paintbrush under water then lift it out; the water films draw the bristles of the brush together. With each cycle of wetting and drying, loose decompacted soils will be drawn together more by these forces known as 'effective stress'. Extreme wetting or flooding of soils and their collapse and drainage can lead to severe compaction and hard setting.

This is exacerbated by chemical instability 'gypsum responsiveness' and can be minimised by inclusion of gypsum application as well as deep ripping. Many of the ancient soils of Western Australia have undergone extreme natural forces in their development. Previous overburden forces, even from glaciers in some places have squeezed sediments and soils together into dense hard layers in the subsoil; extreme wetting and drying events have done this too.

Additionally, there has been opportunity for natural cements made in the soil from compounds of silica, iron and manganese to solidify soil layers in the subsoil; 'coffee rock' is a common example of this in the north-eastern wheatbelt. Many such layers may not be easily or profitably altered by current soil management techniques and caution is advised when considering curative options for the compact layers they form. Subsoils with sufficient macropores have little restriction to drainage and aeration.

Poor aeration leads to the build up of carbon dioxide, methane and sulphide gases, and reduces the ability of plants to take up water and nutrients. The number, activity and biodiversity of micro-organisms and earthworms are also greatest in well aerated soils and are able to decompose and cycle organic matter and nutrients more efficiently.

Roots are unable to penetrate and grow through firm, tight, compacted soils, severely restricting the ability of the plant to utilise the available water and nutrients in the soil profile.

A high penetration resistance not only limits plant uptake of water and nutrients, but greatly reduces fertiliser efficiency and increases the susceptibility of the plant to root diseases.

Soils with good porosity will also tend to produce less greenhouse gases carbon dioxide, methane and nitrous oxide during wetter and warmer conditions. Potential rooting depth is the depth of soil that plant roots can potentially exploit before reaching a barrier to root growth, and generally indicates the ability of the soil to provide a suitable rooting medium for plants.

The greater the rooting depth, the greater the available water-holding capacity of the soil. During dry growing seasons deep roots can access larger water reserves to help alleviate water stress. The exploration of a large volume of soil by deep roots can also access more nutrients. Conversely, soils with restricted rooting limit plant uptake of water and nutrients, reduce fertiliser efficiency, increase leaching and can decrease crop yield.

A high resistance to root penetration can also increase plant stress and the susceptibility of the plant to root diseases. Crops with a deep, vigorous root system help raise soil organic matter levels and soil life at depth.

The physical action of the roots and soil fauna and the glues they produce, promote soil structure, porosity, water storage, soil aeration and drainage at depth.

A healthy root system provides capacity for raising production and may provide significant environmental benefits. Mulch in a perennial garden.

If a mechanical rototiller is used, be careful not to repeatedly go over areas that are already cultivated. Using organic matter like straw or chopped leaves in a vegetable garden that can be mowed and turned into the soil in the spring or fall will add more organic matter. Get a soil test once every three years to check on nutrients, soil pH and percentage of organic matter.

Go to www. For a large vegetable garden, another solution is to grow a cover crop at the end of the season, then mow and turn in the following spring before planting. The roots penetrate the compacted soil and loosen it. By mowing and turning the mowed tops in, the soil is additionally loosened. Cover crops could include annual ryegrass, winter wheat, winter rye, buckwheat, oilseed radishes and hairy vetch. None of these fixes are quick or easy. An awareness of what compacted soils are and how to change them is a lifetime commitment to having better soil and better crops.

For more information on a wide variety of Smart Gardening articles, or to find out about Smart Gardening classes and events, visit www. Download a printable PDF: What to do about compacted soil. This article was published by Michigan State University Extension. What to do about compacted soil. Factors contributing to compacted soil Over-tilling soil. Photo credit: Rebecca Finneran, MSU Extension If a mechanical rototiller is used, be careful not to repeatedly go over areas that are already cultivated.

The key is to wait until the soil is drier and crumbles. Working soil when it is too wet often occurs in the spring when gardeners are anxious to get started. Another form of compaction is mixing sand into clay soils to try to loosen the soil. This creates the opposite of the desired effect and the soil becomes like concrete. The best method for improving soil tilth is to add organic matter such as compost, peat moss or leaf mold.

A fourth form of soil compaction occurs when vehicles often park or drive on a lawn, when construction equipment has frequented an area, or when people repeatedly walk over an area creating a path. Such areas may include where vehicles are parked on the grass, riding lawn mower tires running in the same place over a long period of time, areas where dogs run constantly or the shortest route to the bus stop.

Dead areas indicate where mower tires repeatedly drove over the lawn, compacting the soil. The path between the tires is robust. Once one realizes they have areas with soil compaction problems, there are several things one can do.

Resist the urge to routinely roto-till or cultivate the garden. Instead, consider adding organic matter by using mulch or compost over the top of a flower bed, or hand-spade it into the top 3 to 62 inches of the soil.

For vegetable gardens, put 2 inches of compost on the soil surface and till in and repeat for a total of 4 inches in a growing season.