Soil stabilization


Soil stabilization a general term for any physical, chemical, mechanical, biological or combined method of changing a natural soil to meet an engineering purpose. Improvements include increasing the weight bearing capabilities, tensile strength, and overall performance of in-situ subsoils, sands, and waste materials in order to strengthen road pavements.
Some of the renewable technologies are: enzymes, surfactants, biopolymers, synthetic polymers, co-polymer based products, cross-linking styrene acrylic polymers, tree resins, ionic stabilizers, fiber reinforcement, calcium chloride, calcite, sodium chloride, magnesium chloride and more. Some of these new stabilizing techniques create hydrophobic surfaces and mass that prevent road failure from water penetration or heavy frosts by inhibiting the ingress of water into the treated layer.
However, recent technology has increased the number of traditional additives used for soil stabilization purposes. Such non-traditional stabilizers include: Polymer based products, Copolymer Based Products, fiber reinforcement, calcium chloride, and Sodium Chloride.
Soil can also be stabilized mechanically with stabilization geosynthetics, for example, geogrids or geocells, a 3D mechanical soil stabilization technique. Stabilization is achieved via confinement of particle movement to improve the strength of the entire layer. Confinement in geogrids is by means of interlock between the aggregate and grid, and in geocells, by cell wall confinement stress on the aggregate.
Traditionally and widely accepted types of soil stabilization techniques use products such as bitumen emulsions which can be used as a binding agents for producing a road base. However, bitumen is not environmentally friendly and becomes brittle when it dries out. Portland cement has been used as an alternative to soil stabilization. However, this can often be expensive and is not a very good Environmentally friendly alternative. Cement fly ash, lime fly ash, bitumen, tar, cement kiln dust, tree resin and ionic stabilizers are all commonly used stabilizing agents. Other stabilization techniques include using on-site materials including sub-soils, sands, mining waste, natural stone industry waste and crushed construction waste to provide stable, dust free local roads for complete dust control and soil stabilization.
There are advantages and disadvantages to many of these soil stabilizers.
Many of the environmentally friendly alternatives have essentially the same formula as soap powders, merely lubricating and realigning the soil with no effective binding property. Many of the new approaches rely on large amounts of clay with its inherent binding properties.
Bitumen, tar emulsions, asphalt, cement, lime can be used as a binding agents for producing a road base. When using such products issues such as safety, health and the environment must be considered.
The National Society of Professional Engineers has explored some of the newer types of soil stabilization technology, specifically looking for effective and non-harmful alternatives. One of the examples utilizes new soil stabilization technology, a process based on cross-linking styrene acrylic polymer. Another example uses long crystals to create a closed cell formation that is impermeable to water and is frost, acid, and salt resistant.
Utilizing new soil stabilization technology, a process of cross-linking within the polymeric formulation can replace traditional road/house construction methods in an environmentally friendly and effective way.
There is another soil stabilization method called the Deep Mixing method that is non-destructive and effective at improving load bearing capacity of weak or loose soil strata. This method uses a small, penny-sized injection probe and minimizes debris. This method is ideal for re-compaction and consolidation of weak soil strata, increasing and improving load bearing capacity under structures and the remediation of shallow and deep sinkhole problems. This is particular efficient when there is a need to support deficient public and private infrastructure.

Magnesium chloride

Water absorbing magnesium chloride attributes include
  1. it starts to absorb water from the air at 32% relative humidity, almost independent of temperature,
  2. treated roads can be regraded and re-compacted with less concern for losing moisture and density.
However, limitations include
  1. a minimum humidity level is required to absorb moisture from the air,
  2. it is more suitable in drier climates,
  3. in concentrated solutions it is very corrosive,
  4. it attracts moisture thereby prolonging the active period for corrosion,
  5. rainwater tends to leach out highly soluble chlorides,
  6. if there is a high fines content in treated material then the surface may become slippery when wet,
  7. when less than 20% solution it has performance effectiveness similar to water.
The use of magnesium chloride on roads remains controversial. Advocates claim Cleaner air, which leads to better health as fugitive dust can cause health problems in the young, elderly and people with respiratory conditions; and Greater safety through improved road conditions, including increased driver visibility and decreased risks caused by loose gravel, soft spots, road roughness and flying rocks. It reduces foreign sediment in nearby surface waters , helps prevent stunted crop growth caused by clogged pores in plants, and keeps vehicles and property cleaner. Other studies show the use of salts for road deicing or dust suppressing can contribute substantial amounts of chloride ions to runoff from surface of roads treated with the compounds. The salts MgCl2 are very soluble in water and will dissociate. The salts, when used on road surfaces, will dissolve during wet weather and be transported into the groundwater through infiltration and/or runoff into surface water bodies. Groundwater infiltration can be a problem and the chloride ion in drinking water is considered a problem when concentrations exceed 250 mg/l. It is therefore regulated by the U.S. EPA’s drinking water standards. The chloride concentration in the groundwater or surface water depends on several factors including:
  1. application rate,
  2. composition and type of soil,
  3. type, intensity, and amount of precipitation,
  4. the drainage of the road system.
In addition, the chloride concentration in the surface water also depends on the size or flow rate of the water body and the resulting dilution achieved. In chloride concentration studies carried out in Wisconsin during a winter deicing period, runoff from roadside drainages were analyzed. All studies indicated that the chloride concentration increased as a result of deicing activities but the levels were still below the MCL of 250 mg/L set by the EPA. Nevertheless, the long-term effect of this exposure is not known.
Although the U.S. EPA has set the maximum chloride concentration in water for domestic use at 250 mg/l animals can tolerate higher levels. At excessively high levels, chloride is said to affect the health of animals. As stated by the National Technical Advisory Committee to the Secretary of Interior, “Salinity may have a two-fold effect on wildlife; a direct one affecting the body processes of the species involved and an indirect one altering the environment making living species perpetuation difficult or impossible.” One major problem associated with the use of deicing salt as far as wildlife is concerned is that wildlife are known to have “salt craving” and therefore are attracted to salted highways which can be a traffic hazard to both the animals and motorists.
Regarding the accumulation of chloride salts in roadside soils including the adverse effects on roadside plants and vegetation physiology and morphology, documentation dates back to World War II era times and consistently continues forward to present times. As far as plants and vegetation are concerned, the accumulation of salts in the soil adversely affects their physiology and morphology by: increasing the osmotic pressure of the soil solution, by altering the plant’s mineral nutrition, and by accumulating specific ions to toxic concentrations in the plants. Regarding the intentional application of excessive salts: see Salting the Earth.
Road departments and private industry may apply liquid or powdered magnesium chloride to control dust and erosion on unimproved roads and dusty job sites such as quarries because it is relatively inexpensive to purchase and apply. Its hygroscopy makes it absorb moisture from the air, limiting the number of smaller particles that become airborne. The most significant benefit of applying dust control products is the reduction in gravel road maintenance costs. However, recent research and updates indicate biological toxicity in the environment in plants as an ongoing problem. Since 2001, truckers have complained about "Killer Chemicals" on roads and now some states are backing away from using salt products.
Also a small percentage of owners of indoor arenas may apply magnesium chloride to sand or other "footing" materials to control dust. Although magnesium chloride use in an equestrian arena environment is generally referred to as a dust suppressant it is technically more accurate to consider it as a water augmentation activity since its performance is based on absorbing moisture from the air and from whatever else comes in contact with it.
To control or mitigate dust, chlorides need moisture to work effectively so it works better in humid than arid climates. As the humidity increases the chloride draw moisture out of the air to keep the surface damp and as humidity decreases it diffuses and releases moisture. These naturally occurring equilibrium changes also allow chlorides to also be used as a dehydrating agent including the drying out of and curing and preservation of hides.
As a road stabilizer, magnesium chloride binds gravel and clay particles to keep them from leaving the road. The water-absorbing characteristics of magnesium chloride prevent the road from drying out, which keeps gravel on the ground. The road remains continually "wet" as if a water truck had just sprayed the road.