Soil stabilization as a technique for improving the engineering properties of soil for construction use has been discovered for many years in the construction industry. In the olden day’s construction, different methods of soil stabilization were used in improving soil stability and suitability, some of which were so effective that many of the roads and buildings constructed still exist today. Some of such roads are still in use today such as Fosse Way, Waiting Street, Akeman Street, and many others built by the Romans in Britain dating to 47 AD.
The era of modern soil stabilization started around the 1960s and 1970s when aggregates and fuel resources became scarce and engineers at that time began to reconsider other ways to replace the traditional techniques
of improving poor soils properties at construction sites with boulders and aggregates that have better geological and engineering properties.
This article intended to discuss in detail the different soil stabilization methods obtainable in the construction industry.
What is Soil?
The soil in terms of construction is a natural earthen material that possesses the geotechnical and mechanical properties that can support construction activities and can also be used for construction purposes.
Most civil engineering constructions are done on the earth’s surface and for the stability of the structures a stable soil foundation is usually required to support these structures such as roads, tunnels, bridges, dam structures, towers, irrigation canals, buildings, etc. all of these structures requires a suitable and stable soil foundation base to support them. Most soil materials to be used either as construction materials or as a support base for construction activities their suitability must be examined to ascertain their engineering properties to meet the design requirement and specifications.
In situations where the proposed soil material falls below the design requirements and the engineering specifications, the soil can be subjected to a stabilization process to achieve the properties that can support the proposed designed project. Through research, it has been discovered that proper soil analysis and design of civil engineering structures tend to prevent structural failure, adverse environmental impact, and subsequently the post-construction problems that may occur as a result of improper soil analysis, and design.
Soil stabilization is a technique for transforming, improving, and modifying the geotechnical properties and the engineering characteristics of particular soil material by adding and blending other soil materials with better properties to improve the soil performance. This is a technique for improving the shear strength of soil parameters and thereby increasing the bearing capacity of the soil.
Stabilization becomes necessary when the soil under which the structural foundation will rest cannot bear the proposed structural load. This becomes a remedial measure intended to reduce the permeability and compressibility of the soil materials to the shear strength of the soil and thus reduce the effect of differential settlement of structures on the soil.
The soil stabilization process usually begins in the laboratory where the soil materials in form of samples are scientifically analyzed to determine their stabilization method and the chemical modifiers that will be required to adequately stabilize the soil. A typical laboratory test for determining the types, and quantity of stabilization agents and materials required for proper stabilization of soil materials is Eades and Grim pH test. When the stabilization method and the application rate are determined, soil stabilization is then implemented at the construction site under the strict supervision of an expert.
Soil Stabilization Agents
There are different types of soil stabilizing agents to improve the geotechnical properties such as permeability, compressibility, durability, and strength. Some of the commonly used soil stabilizing agents include the following:
- Lime fly ash
- Cement fly ash
- Tree resin
- Ionic stabilizers
- Cement kiln dust
Soil Stabilization Methods
The soil stabilization methods usually are not a magic tool to transform, modify or improve all types of soil materials for better performance. The quantity of stabilizing agents and their blending proportion usually depends largely on the soil type and the specific soil properties that are to be improved and ultimately the desired result of every engineer is to obtain an improved stable soil volume with adequate strength, compressibility, and permeability to support the intended structural design.
Some of the commonly used soil stabilization methods for improving the geotechnical and the engineering properties of soil materials for better performance are as follows:
- Lime Soil Stabilization Method
- Fly ash Soil Stabilization Method
- Cement Soil Stabilization Method
- Bituminous Soil Stabilization Method
- Rice Husk ash Soil Stabilization Method
- Thermal Soil Stabilization Method
- Electrical Soil Stabilization Method
- Recycled and Waste Products Soil Stabilization Method
- Geotextile and Fabrics Soil Stabilization Method
- Mechanical Soil Stabilization Method
Lime Soil Stabilization Method
The lime soil stabilization method is one of the cheapest stabilization techniques when compared to other methods of soil stabilization.
This method of soil stabilization requires adding lime to the soil to improve its properties and performance. In the lime stabilization method, there are different types of lime used for stabilization which include calcite quick lime, hydrated high calcium lime, monohydrated dolomite lime, and dolomite lime. The amount of lime usually required in most lime stabilization ranges from 5% to 10%.
The lime soil stabilization method largely improves the soil properties by increasing the strength through cation exchange capacity instead of cementing effect produced by the pozzolanic reaction.
This stabilization method can also be identified by the pozzolanic reaction effect when pozzolana materials react with lime in the presence of water to produce cementitious compounds. The result is usually indicated by either hydrated lime in form of Ca(OH)2, or the quicklime in form of CaO.
The major applications of the lime stabilization method are usually in geotechnical and environmental applications.
Fly ash Soil Stabilization Method
Fly ash is usually gotten from burning coal of coal-based power generation plants. There are two major classes of fly ash which include the following:
- Class C fly ash: usually have self-cementing properties and can be substituted for Portland Cement in concrete production and is also used as a stabilizing agent for soil stabilization to modify and strengthen poor soils.
- Class F fly ash: this class of fly ash has very little self-cementing properties compared to class C fly ash but can be mixed with additives such as hydrated lime, cement, or quicklime that create cementitious compounds with the same effect as that of class C.
The Fly ash stabilization method due to its affordability and availability is becoming a more popular stabilization method compared to other stabilization methods and it takes less time to stabilize than any other method.
Cement Soil Stabilization Method
Stabilization of soil with cement is a stabilization method where soil particles are bonded together through the cement hydration process which develops into crystals that can interlock with one another resulting in high compressive strength. In achieving a hard and strong bond between cement and soil particles the material particles must be well coated with cement.
Cement application in soil stabilization starts by determining the required quantities of cement and water ratio. The ratio of the cement-water mixture is carefully controlled to achieve sufficient moisture required for the cement to fully hydrate but no excess water is needed as it would result in to increase in the soil porosity, increase in the water/cement ratio, reduction in the final soil density, reduction in the final strength as well, and would lead to shrinkage cracking. Usually, the amount of cement required is normally determined by laboratory testing and the required water ratio is usually controlled on the site at the time of construction using the simple field-based test.
Bituminous Stabilization Method
Bituminous stabilization is a soil stabilization method by which a controlled quantity of bitumen is thoroughly mixed with existing soil or aggregate material to create a firm and stable base or wearing coast. Bituminous material usually increases the cohesion and load-bearing capacity of the soil and makes it highly resistant to water.
Bitumen soil stabilization is generally executed by using asphalt cutback, asphalt emulsions, or asphalt cement. Ultimately the types of bitumen to be used for any soil stabilization in most cases depend on the type and the nature of the soil to be stabilized, weather conditions, and the method of construction.
Bituminous materials when applied to soil increase soil cohesion and reduce water percolation of the soil.
Rice Husk ash Stabilization Method
Rice husk ash (RHA) is a common by-product of rice milling. It is also used as a soil stabilizer with a lot of environmental benefits. Rice husk ash is usually not self-cementitious, therefore a hydraulic binder such as lime must be added to create a cement bond to improve the soil strength.
Risk husk is usually similar in reaction to fly ash, which is more finely divided. When used for soil stabilization gives great results.
Thermal Stabilization Method
One of the common traditional methods of reducing the plasticity of highly clayey soils is heat treatment commonly known as the thermal stabilization method. This is one of the oldest soil stabilization methods extensively used by Australian agencies in pavement construction.
The thermal soil stabilization method involves the use of a traveling furnace at a temperature over 500°C capable of handling large amounts of soil.
It is also possible to further improve the heat-treated soil with either bitumen or cement. In some cases, to increase the soil reactivity with cement, raw clayey soil is added to the heat-treated soil. This is determined in the laboratory based on compressive strength tests.
Electrical Stabilization Method
Recycled and Waste Products Stabilization Method
There are many waste materials available today such as copper and zinc slag, crushed old asphalt pavement, rubber tire chips, and paper mill sludge which can be used for effective soil stabilization.
Improper plastic waste disposal is becoming an alarming environmental issue in most developing countries. Recycling and using these plastic bottles for soil stabilization is a move in the right direction to make the construction industry an appropriate candidate with its high consumption ability. This is a decent alternative for protecting the environment and clearing the waste of plastic bottles and other plastic wastes.
Geotextile and Fabrics Stabilization Method
Woven geotextile materials are usually produced from porous synthetic materials such as polyethylene, polyester, nylons, and polyvinyl chloride which contain different features to help achieve successful soil stabilization.
The woven geotextile can be used for road stabilization to create a layer between two different soil types. This type of geotextile is made from the polypropylene silt film fabric that offers high strength and resistance to several different aspects of your application in soil stabilization.
Mechanical Soil Stabilization Method
The mechanical Soil Stabilization Method is the process of improving the properties of existing soil by changing its grade. This type of soil stabilization method involves densification and compaction of soil material using applying mechanical energy using various types of heavy construction equipment such as rollers, rammers, vibration machines, and sometimes blasting equipment. In the mechanical soil stabilization method, the stability of the soil depends majorly on the inherent properties of the soil material.
Mechanical stabilization of soils can be achieved by mixing two different types of soil materials of high gradations to create a better material that meets the required specification for stabilization.
This method of soil stabilization is usually used for road sub-base and base courses.