Construction Methods of Soil Stabilization

Soil stabilization can also be described as the process of enhancing the physical, mechanical and chemical properties of soil to increase the strength, durability and load bearing capacity of soil. Through soil stabilization, engineers are able to turn troubled ground into a dependable base of roads, embankments, airports, pavements, and buildings.

This article gives a very brief summary of the soil stabilization methods in construction, their merits, and their drawbacks as well as the current new development.

Table of Contents

The purposes of Soil Stabilization

The major objectives of soil stabilization are:

Pulling Strength: Strengthen the soil in order to support more loads.
Reducing Plasticity: This aims at enhancing workability through reduction of plastic index of the soil.
Volume Control: Reduce expansion and contraction of expansive soils.
Enhancing Durability: Enhance weathering, erosion and traffic loads resistance.
Water Control: Low permeability and enhance drainage.
Cost Optimization: Implement the utilization of the soils that are available locally rather than the imported fill which is costly.

Issues affecting Soil Stabilization

Engineers consider a number of factors before choosing a stabilization technique:

Soil Type: Clay, silt, sand or organic soil all have varying treatment requirements.
Moisture Content: Water has an impact on the strength and reactivity of soil with additives.
Load Requirements The different stresses are imposed on roads, runways, and buildings.
Environmental Conditions: Performance is affected by freeze-thaw cycles, rain, and levels of groundwater.
Economics: Stabilising materials availability and cost.
Construction Time: There are several methods that give quicker results than others.

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Categorization of Soil Stabilization Methods

Two broad categories of soil stabilization methods are in existence:

Mechanical Stabilization- This relates to physical processes like compaction, mixing or reinforcement.

Chemical Stabilization- Addition of chemicals to modify the soils.

The third category that is commonly thought of nowadays is biological and advanced methods that are eco-friendly and modern technological approaches.

Let us explore each in detail.

Mechanical Soil Stabilization.

Mechanical stabilization does not alter chemical composition of soil and only alters the soil properties. It is normally physical manipulation and enhancement of soil gradation or density.

a) Compaction

Definition Process of making soil dense by mechanical means of filling air spaces.
Machines Involved: Rollers, (sheep foot, smooth drum, vibratory), rammers, and tampers.
Uses: Road embankments, foundations and pavements.
Benefits: Easy, inexpensive and enhances shear strength and bearing capacity.
Limitations: No good use in highly organic soils or soils with high moisture content.

b) Soil Replacement

Soil that is weak is dug up and substituted with stronger and well-graded soil like gravel, sand or crushed rocks.
Applied in shallow foundations when the bad layers of soil are near the surface.
Only economical in the case of small soil thickness that is weak.

c) Blending of Soils

Combining two or more soils of varying gradations to become more stronger and stable.
Example: Plasticity versus strength- mixing clay with sand.

d) Geosynthetics and Strengthening.

Geotextiles, geogrids, geomembranes are laid in between the layers of soil to reinforce the soil. They enhance the distribution of loads, minimize settlement and avert soil erosion.
Applications are in highway construction, retaining walls, and slope stabilization.

Stabilization of Soils Chemically.

Chemical stabilization is the process of adding stabilizers which react with mineral components in the soil or change its structure to enhance properties.

a) Lime Stabilization

Procedure: Clayey soils are combined with Quicklime (CaO) or hydrated lime (Ca(OH) 2 ).
Reactions: Lime lowers plasticity, through a cation exchange reaction and pozzolanic reaction, which produce cementitious compounds.
Advantages: It decreases shrink-swell, improves workability and strengthening.
The uses: Highway subgrades, airport runways, and highway embankments.
Limitations: Can not be used in sandy or silty soils.

b) Cement Stabilization

Process: Soil is compacted with Portland cement.
Reactions: Cement reacts with soil moisture and creates a stiff structure, which cement binds particles.
Merits: Gives it high compressive strength and durability.
Uses: Road bases, foundations and slope protection.
Limitations: It is expensive and has to be mixed and cured.

c) Bituminous Stabilization

Procedure: Bitumen or asphalt is combined with soil to cement particles to eliminate water infiltration.
Advantages: Makes soil waterproof, pliable and traffic load resistant.
Uses: Construction of pavements particularly black cotton soils.
Disadvantages: Expensive, environmentally unfriendly, heat sensitive.

d) Chemical Additives (Salts, Chlorides, Polymers)

Calcium chloride and sodium chloride: Lower frost prone areas in chilly conditions.
Polymers and resins: enhance the strength and decrease permeability.
Fly ash and industrial by-products: This one is used with lime or cement in order to increase strength.

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Biological and environmentally-friendly Stabilization.

Newer environmentally friendly approaches are being taken with sustainability taking priority.

a) Enzyme Stabilization

Enzymes are organic catalysts which combine with soil minerals to form more bond and density.
Solid concrete used when building low-cost roads in country districts.

b) Microbial-Induced Calcite Precipitation (MICP)

Some bacteria like Sporosarcina pasteurii dissolve calcium carbonate in the pores of soil.
Increases strength and decreases permeability.
Green and research active.

c) Bio-polymers

Soil particles are held together using natural polymers such as guar gum, xanthan gum and lignin.
They enhance water resistance and soil stability and do not have a significant negative effect on the environment.

Application of Soil Stabilization in the field.

Highway and Road Construction- Strengthening subgrades and sub-bases.
Airfields – Stabilized soil runways give smooth and firm surfaces.
Railways -Improves the support of ballast and lowers the settlement of the tracks.
Building Foundations – Strongly deters soil- Prevents settling in weak soils.
Slope Stabilization-Geosynthetics and reinforced soil helps in the prevention of landslide.
Embankments and Dams- Soil stability is achieved by making it impermeable and durable.

Benefits of Soil Stabilization.

Takes advantage of locally available soil, which makes finding sources of the borrowed materials more expensive.
Improves the load carrying capacity and lifetime of foundations.
Less maintenance requirements of pavements and structures.
Offers alternatives that are sustainable through reuse of industrial wastes such as fly ash and slag.
Eliminates the dangers of weak soils.

Disadvantages of Soil Stabilization.

The effectiveness is dependent on the soil type and environmental conditions.
Certain ones (cement, bitumen) may be expensive.
Ecological issues may occur when chemical stabilizers are not properly applied.
It needs experienced workforce and quality control.
Aggressive climates can lower performance in the long-run.

New Things that have happened in Soil Stabilization.

Nano-materials: Nano-silica and nano-clay are those which enhance properties of soils at the micro-scale.
Cold Pavement Recycling: Recycles the asphalt and lays it with foamed bitumen or cement.
Green stabilization: Agricultural wastes such as rice husk ash, bagasse ash or coconut coir used.
Smart monitoring: Sensors installed within layers of soil will monitor the stability of soil performance over time

Case Studies:

Metro Rail Project (Delhi, India): The weak alluvial soils were stabilized using lime and cement.
Rural Roads in Africa: Enzyme stabilization was a cost effective and sustainable pavements solution.
Earthquake-Prone Areas of Japan: Cement deep soil mixing (CDSM) technique of stabilizing the loose sandy soils against liquefaction.
Best Practices to Soil Stabilization.
Carry out adequate soil exploration and classification.
Choose stabilizer according to the needs of the project and the type of soil.
Make sure that it is mixed, compacted and cured.
Conduct quality control tests like CBR, UCS and Atterberg limits.
Take into account environmental and sustainability.

Conclusion

The process of soil stabilization is important in contemporary construction since it converts weak soils into stable foundations. Engineers now have vast options of techniques, including traditional mechanical compaction, or state-of-the-art biologically enhanced techniques. The choice of the appropriate approach is determined by the type of soil, the needs of the project, and price as well as the environment.

With the growing construction activities and the increased emphasis on sustainability, new, eco-friendly, and cost-effective soil stabilization methods, including bio-polymers, microbial stabilization, and use of industrial by-products, are the future of soil stabilization.

Through the correct soil stabilization methods, the construction projects can be made to be durable, safe and cost-effective and at the same time reducing their effects on the environment.

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