Three Broad Types of Soil Stabilization

There are three broad types of soil stabilization: biological, physical and chemical.

Biological soil stabilization:

It is achieved through afforestation or planting, and its main purpose is erosion control. Root traits such as architectural, morphological, physiological and biotic play an important role in both the physical and chemical development of soils enabling structural stability of the soil. This method is suitable for terrain exposed to water and wind influences, which are not meant for building. However, initially, planting has to be supported by other types of soil stabilization from the moment seeds or seedlings are planted till the moment the plants become strong. Otherwise, along with the surface layer, seeds or young plants would be carried away by water flow or wind.

Physical soil stabilization:

It is the modification of soil particle size distribution and plasticity by the addition or subtraction of different soil fractions in order to modify its physical properties. Mechanical stabilization is the modification of soil porosity and interparticle friction or interlock. The two methods work synergistically together to yield soil stabilization. Physical and mechanical types of soil stabilization include five different types of techniques namely; compaction, pre-wetting, wetting-drying cycles, reinforcement and solid wastes. Compaction is widely used in soil stabilization and it uses mechanical means for the expulsion of air voids within the soil mass so that the soil can bear load subsequently without further immediate compression. Pre-wetting is a primitive method that was applied in the past for mitigation of swelling in the soil through saturating soil by creating a moisture-rich environment which results in the soil absorbing water and swelling hence creating a construction heave. Fundamentally, a saturation of the soil causes it to swell so that ensuing wetting would not end up in harmful heaving because the soil maintains a constant volume at a very high moisture content. 

Wetting dry cycles involve saturating the soil with water until full swelling then followed by a corresponding drying of the soil to its initial water content. Repetitive cycles are performed until an equilibrium state is reached in which the plastic deformation gradually disappears. Soil reinforcement is a mechanical means of stabilizing weak soils using fibrous materials which can be in the form of geosynthetics or fibres of a natural or synthetic origin. The reinforcements form a spatial 3D network in favour of interlocking the soil grains into a unit mass of improved mechanical performance and resultant stability. Solid wastes such as municipal wastes in the form of plastic, glass, wood, e-waste, rubber from end of life tires, plant debris, metals and other organic materials are the main constituents. Glass powder is a good soil stabilizer because of good heat resistance, its transparency, breakage and pressure resistance, cost-effective and very chemical resistant. On the other hand, e-waste also has good heat resistance, corrosion resistance, flexibility, lightweight, durable and cost-effective. 

The drive for a circular economy over recent years has also found space in the repurposing of waste solid materials in soil stabilization.  Two different stabilization systems, one is drainage and another one is compaction. Drainage is beneficial as it removes excess water from the soil. Water makes the soil more plastic and thus prone to deformation occurrence. Excessive water in the soil can also cause erosion. The drainage system consists of a set of pipes, canals and/or pumps, which makes it quite expensive to build. Compaction makes soil denser and thus less compressible and more water-resistant, but for most of the soils this method alone is not sufficient. It is usually an additional measure to chemical stabilization.

Chemical soil stabilization:

It can be achieved through the use of traditional and non-traditional agents. The distinction between the two classes exists as a result of the pre-existing and well-established additives as compared to the most recently developed agents. Examples of traditional chemical stabilization agents include lime, cement, bitumen and fly ash and they are usually calcium-based.

On exposure to water, they undergo both short- and long-term chemical changes resulting in overall enhancement of the soil matrix with regards to swell reduction, shear strength improvement and resistance to influence of wetting and drying. The mechanisms of stabilization for traditional chemical stabilizers include cation exchange, flocculation, agglomeration, pozzolanic reaction and carbonate cementation. Non-traditional agents react chemically with soil in the presence of sufficient moisture to produce physicochemical interactions in the soil. Examples include but are not limited to bitumen emulsions, cement kiln dust, ground granulated blast furnace slag, pulverized coal bottom ash, steel slag, mine tailings, sulphonated oils and polymers. They are achieved through application of various substances which act as compaction aids, water repellents and/or binders. The most effective stabilizer is, of course, one that has all three possible characteristics. These substances are usually diluted with water and sprayed over soil which can be followed by mixing and compaction

Cement soil stabilization: is the oldest and still very common soil binder. Cement can be used for the stabilization of a wide range of soil types – and is very effective in pavement stabilisation. However, cement application has many limitations as the organic content in soil should be generally limited to 2%  in additional to non-compatibility with soils with high amount of clay. The soil should also be free from deleterious salts such as sulphate which affect the setting time of the cement and result in subsequent disruption of the soil-cement structure. It is not compatible with soils with high amount of clay. On the other side certain concentration of clay is necessary for the method to be successful. Any presence of organic material is not allowed. Application process is quite complicated. High control of water content has to be performed, as well as demanding procedure for determination of right time for compaction. If viewed from economic and environmental aspect, cement production is extremely energy demanding.

Lime soil stabilization: Among chemical types of soil stabilization, lime application is also very common. The lime maybe used in different forms namely hydrated high-calcium lime, monohydrated dolomitic lime, calcitic quicklime, and dolomitic quicklime. The calcium in the lime exchanges with adsorbed cations of the clay mineral causing the clay to flocculate, thus reducing PI of clays as it becomes more workable and mixable.  Lime compounds mostly used are calcium hydroxide Ca(OH)2 and dolomite Ca(OH)2+MgO. Lime is produced through a very energy demanding process and with high carbon dioxide emissions. Clayey materials are most suitable for lime stabilization, if they have PI values lower than 10. Pozzolanic reaction occurs in some clays, resulting in the formation of cementing agents that increase the strength of soil. It is not good stabilizer for silts, granular materials and soils with sulphate contents greater than 0.3 percent. If the treated material is not protected from runoff, some lime could be washed into the surrounding environment and have an impact by raising the pH.

Bitumen soil stabilization: can occur in different forms either as bitumen, cutback bitumen or bitumen emulsions. Selection of type and grade of bitumen is soil type, construction method and weathering conditions dependent. The most important parameters affecting bitumen stabilization include moisture content, bitumen viscosity, bitumen content, uniformity in mixing, aeration, compaction, and curing. The mechanism of action in bitumen stabilization involves binding that it imparts to the soil particles making it more weather resistant. Consequentially, the lack of water ingress leads to a significant improvement in soil strength as well as weather resistance capacity. Presence of organic matter, dissolved salts and high pH values of soils negatively affects bitumen stabilization. The quantity of bitumen required varies from 4% to 7% with higher than optimum values filling voids between soil or aggregate particles which results in poor compaction, decreased strength and compromised deformation behavior of the stabilized soil. 

Fly ash soil stabilization: is another popular chemical stabilizer. It is a by-product of coal fired electric power generation facilities. The mechanism of soil stabilization using fly ash is the pozzolanic reaction and the filing of the voids in the mix. It is among types of soil stabilization suitable for coarse grained particles with little or no fines. Soil to be stabilized should have low moisture content. After proper amount of fly ash added, an activator is usually used to intensify pozzolanic reaction in the mixture because fly ash produced from the combustion of harder, older bituminous, anthracite coal is pozzolanic but not self-cementing. The activator is lime or Portland cement in rate 20 to 30 % of fly ash.  Fly ash contains heavy metals and other harmful compounds which leach easily into soil and water bodies.

GRT offers soil solutions for all types of soil stabilization issues:

Erosion control measure or surface stabilisation can be achieved by application of GRT: Enviro-Binder. It is a polymer-based erosion control that is added to water to reduce soil erosion by binding soil particles that would otherwise be carried away by surface water runoff. GRT: Enviro-Binder also can improve germination rate through creating optimal soil conditions through retaining water, nutrients and plant protecting substances for longer periods.

Structural stabilization is achievable through use of GRT9000 and GRT: PCM. These agents act as a high performing stabilizers and binders that works perfectly with our polymer sealant, GRT7000. When it comes to soil stabilization it is suitable for stabilizing granular subgrade, sub base and base of haul roads, side tracks, car parks, construction or military camps, container hardstands, railroad yards, and temporary landing areas.

GRT product applications are among types of soil stabilization applicable to all kinds of soils under various harsh climate conditions. They are independently verified as environmentally sustainable, manufactured to ISO9001 standards and have been comprehensively reviewed by leading independent testing institutions and major companies worldwide.

What are the benefits of soil stabilization? 

1. Enhances the physical and/or mechanical properties of a soil for a specific application. 
2. Improves durability and strength, where the locally available soil is poor 
3. Increased resistance of soil to loading.  
4. Enables use of environmentally friendly products which feeds into the Earth Stewardship approach to material use. 
5. Dust suppression is achieved through soil stabilization which improves workplace health and safety 
6. Erosion and sediment control is prioritized through soil stabilization hence offering protection to topsoil and its nutritional value. 

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REFERENCES

Andavan, S., and Kumar, B.M. 2019. Case study on soil stabilization by using bitumen emulsions-A review. Materials Today: Proceedings. 

Hall, M.R., Najim, K.B., and Dehdezi, P.K. 2012. Soil stabilization and earth construction: materials, properties and techniques. Book chapter. Woodhead Publishing Limited. 

Hudek, C., Sturrock, C.J., Atkinson, B.S., Stanchi, S., Freppaz, M. 2017. Root morphology and biomechanical characteristics of high-altitude alpine plant species and their potential application in soil stabilization. Ecological Engineering.

Ikeagwuani, C.C. and Nwonu, D.C. 2019. Emerging trends in expansive soil stabilization: A review. Journal of Rock Mechanics and Geotechnical Engineering. 11. 423-440.

Rai, A.K. Singh, G., and Tiwari, A.K. 2020. Comparative study of soil stabilization with glass powder, plastic and e-waste: A review. Materials Today: Proceedings.