The soil stabilization method is defined as a method of altering or modifying soil properties to improve the engineering characteristics and performance of soil. The soil Stabilization Method in other words can be defined as the various methods used for modifying the properties of a soil to improve its engineering performance.
Soil stabilization included the mixing of special soil, cementing material, or other chemical materials that are added to natural soil to improve one or more of its properties.
It can also be done by mechanically mixing stabilizing agents and natural soil together so as to achieve a homogeneous mixture or by adding stabilizing material to the soil deposit.
Soil stabilizing methods is used to improve the properties of road base soil. These soil stabilizing agents can improve and maintain soil moisture content, increase soil particle cohesion, and acts as cementing and waterproofing agents.
Civil engineering faces difficult problems while road base soil is found to be clay soil. Soils that have more clay content generally have a tendency to swell more when their moisture content is allowed to increase.
There are much research has been done to improve soil properties by soil stabilization methods using various additives. In most cases, clay soil in pavement work is cement and lime stabilization.
What is Soil?
Soil is defined as a mixture of organic matter, minerals, gases, liquids, and infinity organisms that all in combined form support life on earth. Soils are generally gone under development or changes by physical, chemical, and biological processes, which include weathering with associated erosion. The majority of soil stabilization methods are employed for soft soil in order to achieve desirable engineering properties.
As per the research of Sherwood, small-sized or fine-grained materials can be easily stabilized due to their large surface area in relation to their particle diameter. So, the clay soil surface area compared to others has a large surface area due to flat and elongated particle shapes. On the other hand, silty soil materials are sensitive to small changes in moisture and, therefore, may prove difficult during stabilization.
What Is Soil Stabilization?
Soil stabilization is a method of improving soil properties by adding and mixing other materials to it. Soil stabilization is a method of enhancing the shear strength parameters of soil and thus increasing the bearing capacity of the soil.
It is generally required when the soil under the foundation for construction is not suitable to carry the structural load. Soil stabilization methods is a remedial measure that reduces soil permeability and compressibility of the soil mass in earth structures and to increase its shear strength and which helps in reducing the settlement of structures.
The soil stabilization methods involve the use of the stabilizing agents in weak soils to improve its geotechnical properties such as compressibility, strength, permeability, and durability.
Soil Stabilization Methods
In road construction work, soil and gravel are used as the main ingredients in pavement layers. For that, it required proper tensile stresses and strains spectrum, the soil used for constructing pavement should have a special specification.
By using soil stabilization unbound soil materials can be stabilized with cementitious materials (cement, lime, fly ash, bitumen, or a combination of these). The stabilized soil mass has higher strength, lower permeability, and lower compressibility than the native soil. Soil stabilization can be done in two ways,
1) In situ stabilization and
2) Ex – situ stabilization.
Note that, stabilization method is not magic tools by which every soil properties can be improved for better. The amount of additives and mix proportion depends on which soil properties have to be modified. The major and important properties that every engineer wants to improve are volume stability, strength, compressibility, permeability, and durability.
Some stabilization techniques are listed below,
- Mechanical Stabilization
- Lime Stabilization
- Cement Stabilization
- Chemical Stabilization
- Fly ash Stabilization
- Rice Husk ash Stabilization
- Bituminous Stabilization
- Thermal Stabilization
- Electrical Stabilization
- Stabilization by Geotextile and Fabrics
- Recycled and Waste Products etc.
1. Mechanical Soil Stabilization Method
The mechanical Soil Stabilization Method is the method of improving soil properties by changing its gradation. This method of soil stabilization methods includes compaction and densification of soil matter by application of mechanical energy using various sorts of rollers, rammers, vibration techniques, and sometimes blasting. The stability of the soil generally depends on the inherent properties of the soil material.
In this method, two or more natural soils are mixed together which is superior to any of its components. Mechanical stabilization of soils is done by mixing or blending soils of two or more gradations to obtain a material meeting the required specification.
2. Lime Soil Stabilization Method
Lime stabilization is one of cheapest soil stabilization method.
The soil stabilization method in which lime is added to the soil to improve its properties is known as lime stabilization. There are different types of lime used like hydrated high calcium lime, monohydrated dolomite lime, calcite quick lime, dolomite lime. The amount lime generally added in most soil stabilizer is in the range of 5% to 10%.
Lime Soil stabilization method improvement properties show by increase in strength brought by cation exchange capacity rather than the cementing effect brought by the pozzolanic reaction.
Lime stabilization also indicated by the pozzolanic reaction in which pozzolana materials react with lime in presence of water to produce cementitious compounds. The effect created is indicated by either quicklime, CaO, or hydrated lime, Ca(OH)2.
Lime stabilizations method is most widely utilized in geotechnical and environmental applications.
It has some important applications like an encapsulation of contaminants, highway, slope stabilization, rendering of backfill, and foundation improvement.
However, any existence of sulphur and organic materials may inhibit the lime stabilization process. Sulphate (e.g. gypsum) generally reacts with lime and swell, which may have an effect on soil strength.
3. Cement Soil Stabilization Method
Soil cements stabilization, in which soil particles are bonded together by the cement hydration process which grows into crystals that can interlock with one another giving a high compressive strength. To achieve a hard and strong bond between soil particle cement particles need to coat most of the material particles.
To assure good contact between cement and soil particle for proper bond and efficient soil stabilization, cement particle must be well mixed with certain particle size particles of soil. Soil-cement is generally known as a highly compact mixture of soil, cement, and water.
Soil – cement bond material is hard and durable material as the cement hydrates and develops strength. Cement stabilization is mostly employed when the compaction process is continuing. When cement is added in the soil is fills the void between the soil particles, the void ratio of soil is reduced.
As cement and soil particles mixed well the water is added to the soil, cement reacts with water and goes hard. So, the unit weight of the soil is increased. As cement in the soil get harder the shear strength and bearing capacity are also increased. Cement in stabilized soil decreases the liquid limit and increase the plasticity index and workability of clayey soils.
It is fact that Cement chemical reactions are not dependent on soil minerals, and the key role is its reaction with water that may be available in any soil. This is the primary reason that cement is mostly used to stabilize the soil of any type.
4. Chemical Soil Stabilization Method
Chemical stabilization of soil is a method of modifying the physical-synthetic around and within clay particles in which the earth obliges less water to fulfill the static imbalance.
Calcium chloride generally has the property of hygroscopic and deliquescent is used as a water-retentive additive in mechanically stabilized soil bases and surfacing. This process lower vapor pressure, surface tension increases, and the rate of evaporation decreases.
It also lowers the freezing point of water and which helps in the reduction of frost heave action. It lowers the electric double layer, the salt reduces the water pick up and thus the loss of strength of fine-grained soils. Calcium chloride generally acts as a soil flocculent and facilitates compaction.
Frequent application of calcium chloride may result in loss of chemical by leaching action. For making effective application of salt, the relative humidity of the atmosphere should be above 30%. Sodium chloride is also can be used for this same purpose with a stabilizing action similar to that of calcium chloride.
Sodium silicate is also yet another compound that is used in combination with other chemicals such as calcium chloride, alkyl chlorosilanes, siliconites, polymers, chrome lignin, amines, etc.
5. Fly ash Soil Stabilization Method
Fly ash stabilization is nowadays becoming more popular due to its wide availability. Fly ash stabilization is an inexpensive method and takes less time than any other method. Fly ash wide history in the past and present as an engineering material and has been trustfully employed in geotechnical applications.
Fly ash is a by-product or waste product for coal-based power generation plants. Fly ash little or fewer cementations properties compared to lime and cement. It is known as secondary binders; because these binders cannot produce the desired effect on their own. However, in the presence of primary binders, it can react chemically to form a cementation compound that contributes to improved strength of soft soil.
However, soil fly ash stabilization has below stabilization;
(a) Soil stabilized by this method has low moisture content; therefore, dewatering may be required.
(b) In this method soil and fly ash cured below zero and then soaked in water are highly susceptible to slaking and strength loss.
(c) Fly ash may add expansive minerals in the soil-fly ash mixture, which reduces the long term strength and durability.
6. Rice Husk ash Soil Stabilization Method
Solid waste disposal by landfilling can be reduced by reusing such waste which is having desirable properties such that they can be utilized for various geotechnical application viz. land reclamation, construction of embankment, etc. There is a various method used to improve the soil properties by stabilization that includes densification (such as shallow compaction, dynamic deep compaction, pre-loading), drainage, inclusions (such as geo-synthetics and stone columns), and stabilizations.
The Rice Husk Ash is of suitable material that appears to be an inert material with the silica in the crystalline form suggested by the structure of the particles, but it also may react with lime to form calcium silicates. Risk husk is similar reactive to fly ash, which is more finely divided. So Rice Husk Ash can be used for soil stabilization method would give great results.
7. Bituminous Stabilization
The bituminous soil stabilization method is the method in which is a suitable amount of bituminous material is added and mixed in soil or aggregate material to produce a stable base or wearing surface. Bituminous materials in the soil increase the cohesion and load-bearing capacity of the soil and render it resistant to the action of water.
Bitumen stabilization of soil is generally done by using asphalt cement, asphalt cutback, or asphalt emulsions. The types of bitumen to be used for stabilization is generally depends on the type of soil to be stabilized, method of construction, and weather conditions. Tar binders in frost are must be avoided because of its high-temperature maximum susceptibility.
Asphalts and tars are mostly used in pavement construction as bituminous materials. Bituminous materials when added to soil improves soil cohesion and reduced water absorption.
8. Thermal Stabilization
Thermal change in soil properties can significantly improve the properties of the soil. Thermal stabilization is done by both cooling and heating of soil.
Heating: when soil is heated, its water content is decreasing. This change will decrease electric repulsion between clay particles and the strength of the soil is increased.
Freezing: cooling of any soil is generally resulting in a small amount of loss of strength due to an increase in interparticle repulsion. However, in case, if the soil is cooled to the freezing point the pore water freezes, and the soil, is stabilized.
9. Electrical Stabilization
Electrical stabilization is generally done by using one of the known methods as electro-osmosis. When direct current is passed through a clayey soil, pore water is transferred towards the negative electrode (cathode).
This change is generally happening due to the presence of positive ions (cations) that are present in the water towards the cathode. Due to the removal of water, the strength of the soil is considerably increased. Electro-osmosis is one of the costly methods of soil stabilization method mainly used for drainage of cohesive soils. Incidentally, this method also improves the properties of soil.
10. Stabilization by Geo-textile and Fabrics
Geotextiles are made from porous synthetic materials such as polyethylene, polyester, nylons, and polyvinyl chloride. There is a different variety of geotextile available like woven, non-woven, and grid. Geotextiles materials generally have high strength.
When geotextile properly combined and embedded in the soil which will contribute to its stability. This type of soil stabilization method generally used for the construction of unpaved roads over soft soils. Reinforcing the soil by geotextile materials or metallic strips and providing an anchor or tie back to restrain a facing skin element.
Past research has shown that the load-bearing and strength of subgrades and base course of soil materials can be improved through the addition of no biodegradable reinforcing materials, such as fibers, geotextiles, geo-grids, and geo-composites.
These materials can improve the quality and durability of future highways and may reduce the cost of construction. At present, lots of research and studies are going on these materials based on tests conducted in the laboratory that are only partially complete. Detailed study and practical research are essential for the future use of geotextile materials.
11. Recycled and Waste Products
There are lots of waste material in the world and proper disposal of such waste materials as crushed old asphalt pavement, copper and zinc slag, paper mill sludge, and rubber tire chips are essential to developing proper and effective soil stabilization method.
There is a service need to recycle hazardous materials, it will be necessary to develop a realistic, economical, and effective means of assessing the risk of pollution posed by these materials through leachates and emissions.
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