Soil Stabilization Methods

Road and civil engineering projects demand high-performance and high-quality soils. Soil stabilization involves the alteration of one or more of the soil properties collectively using techniques of modification to enhance both the physical and mechanical properties of the soil for specific applications through controlled modification of soil texture, plasticity, structure and durability. The suitability of the soil for construction purposes is measured in terms of the size and distribution of its particles and as such is described as well-graded or poorly graded. The main purpose of undertaking the process is to prepare the land and build a strong foundation that can support the design loading. Processes including compaction and potentially stabilization to increase soil strength and durability as well as to suppress dust formation and prevent soil erosion. The advantages of soil stabilization include significant improvement of durability and strength and hence bearing capacity and eliminate the need for expensive surface treatments. Dust control, waterproofing and promotion of the use of waste geomaterials in construction are amongst many other reasons. However, the cost of raw materials can be increased with limitations due to location and expenses incurred due to the transportation of raw materials in cases where marginal materials cannot be utilized. 

The methods used to improve the engineering properties of soil are broadly classified into two categories –

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  • Chemical stabilization
  • Mechanical stabilization

CHEMICAL SOIL STABILIZATION

Chemical stabilization alters the chemical properties of the soil through the use of admixtures. Studies have shown about 18 different chemical mechanism namely: exchange of cations, exchange of anions, adsorption, fixation, formation of new minerals, cementation, salt conversion, modification of water films, adsorption of water films, enrichment of pore water with ions, modification of capillary forces, modification of the electrical surface tension of clay minerals, modification of the electrical forces between particles, modification of chemically bound water, adsorption of chemically bound water, neutralization of acids, neutralization of bases, and proton exchange. Outcomes that are expected can be obtained from laboratory tests, the quantity required for chemical additives needed to effectively achieve stabilization is usually small, the chemical mechanism is not time intensive and effectiveness regardless of soil engineering properties are some of the benefits of chemical stabilization 

The limitations of chemical soil stabilization include disparity between simulated laboratory and field conditions could render insitu application impossible, the risk of groundwater contamination is very high as a result of release of toxic compounds from some of the traditional agents as the leachate of toxic chemicals can affect the environment and human life in general, the balance between cost of chemical soil stabilizer and quantity required to achieve effective stabilization can be a challenge and in prevalent unsuitable conditions the effect of chemical stabilization can result in further detrimental conditions of the soil for instance in the soil-lime-sulphate reactions and stabilization induced cracking. 

A significant challenge with chemical soil stabilization is that one needs to have a good engineering judgment – which only comes from experienced engineers and technicians managing the process. The type of soil, the right additive, the right amount to be used and the right application process are aspects to factor in when using this method of stabilizing soils. If either of them goes wrong, the end result can be the opposite of the desired ones resulting in a total waste of time and higher monetary losses. Additives are combined with the soil using heavy-duty machinery. The best machine to achieve the task is a stabilizer / reclaimer rotary mixer. It breaks up the soil and mixes the additive mixture as evenly as possible. The other equipment used to accomplish the task includes water tankers, motor graders, pad foot rollers, rubber tyre rollers.

There are different types of additives available on the market. As already mentioned above, specific additives work with specific soil types. Portland cement, quicklime or hydrated lime, fly ash, calcium chloride and bitumen as some of the mechanical and chemical additives added to it. Chemical additives work differently to stabilize soils. Some act as binders, other increase soil density while a few alter the effect of moisture on the soil.

MECHANICAL SOIL STABILIZATION

Mechanical stabilization involves the use of physical processes. It is the modification of soil porosity and inter-particle friction or interlock for example by compaction. Unlike chemical stabilization, it changes only the physical properties of soil through compaction, soil blending (adding fibrous and non-biodegradable reinforcement) or placing a barrier on the soil.

In geotechnical engineering, soil compaction is a process wherein pressure is applied to soils by means of heavy machinery. It displaces air from the pores and causes soil densification. 

The mechanism to mechanical stabilization involves addition of different grades of materials to achieve a dense packed material and addition of small amount of fine materials as binders for non-cohesive soils to enhance strength of the material. Sands and gravels with strong angularity impart internal friction and incompressibility to the mix, which renders stabilization with addition of a suitable binder loading. Mechanical stabilization also promotes use of locally available materials in a fit for purpose approach and utilization of mine tailings, coral, shell, clinker, slags and construction waste just to mention but a few. 

The factors affecting mechanical stability of soils include; 

  • Mechanical strength and purity of the constituent materials 
  • Percentage of materials and its gradation in the mix 
  • Degree of soil binding taking place 
  • Mixing, rolling, and compaction procedures adopted in the field
  • Environmental and climatic conditions 

Regulating the amount of pressure when compacting is important as excess pressure disintegrates soil aggregates and causes them to lose their engineering properties. Soil reinforcement is another method employed in mechanical stabilization of soils. In this method, soils are reinforced by adding geotextiles and plastic mesh to arrest soil erosion and change features such as soil permeability. Geosynthetic materials such as geogrids and geotextiles are used in mechanical stabilization improve soil strength and soil engineering properties through particle interlocking, confinement, frictional resistance and tensile strength. Besides this, graded aggregate materials are added to soils to decrease soil plasticity.

Strategies for the ground are integral to Global Road Technology’s services. It has developed a range of liquid soil stabilizers that bring in improvements such as enhanced strength, higher density, reduced water permeability and better bearing capacities. The products are designed to be environmentally-friendly and are easy to apply for a number of applications.

Conclusion

Global Road Technology staffing capabilities consist of experienced civil engineers, water engineers, geo-technical engineers, environmental engineers and industry experts to ensure we always have the right qualified onsite technicians and staff to assist with any soil stabilization project.

It’s our goal to keep industries moving, create better roads for rural communities, and safer road infrastructure in low to middle income countries.

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REFERENCES 

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. 

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.

Patel. A. 2019. Geotechnical Investigations and Improvement of Ground Conditions. Woodhead Publishing Limited.