Stabilization of expansive soil is being done for as long as 100 years and many improvements have come in the stabilization methods.

Common methods are

Chemical Stabilization

Mechanical Stabilization such as vibrofloatation (also use cement slurry).

There are various report available on internet, you can download such as:

DESIGN PROCEDURE FOR PAVEMENTS ON EXPANSIVE SOILS: VOLUME 1

Texas Transportation Institute The Texas A&M University System College Station, Texas 77843-3135

Two suggestion according to our local experiences:

Stabilization of expansive soil is being done for as long as 100 years and many improvements have come in the stabilization methods.

Common methods are

Chemical Stabilization

Mechanical Stabilization such as vibrofloatation (also use cement slurry).

There are various report available on internet, you can download such as:

DESIGN PROCEDURE FOR PAVEMENTS ON EXPANSIVE SOILS: VOLUME 1

Texas Transportation Institute The Texas A&M University System College Station, Texas 77843-3135

For urban pavements, most of these methods may be generally ruled out, either on technical and/or economical grounds. Amongst these methods are: the complete removal and replacement of these soils; pavement encapsulation; subgrade pre-wetting by ponding or open flooding, bore hole or trench flooding; chemical stabilization using lime in shallow surficial mixing, shallow pre-drilled lime-filled boreholes, or deep pressure-injected grouting with lime or lime and fly-ash. Pavement construction is increasing day by day due to increase in traffic volumes. Rapid urbanization and industrialization resulted in exponential growth of vehicular population that created huge demand for more number of highways and express way. Expansive soils are those clay soils which exhibited significant volume changes as results of soil moisture variation. This type of soil, upon wetting and drying, causes severe damages to pavement constructed on such soil. Generally, pavements on expansive subgrade soils show early distresses causing the premature failures of the pavement structure. Expansive soils usually have undesirable engineering properties, such as low bearing capacity, coupled with low stability and excessive swelling. The nature of these soils creating serious problems to the civil engineering structures particularly road pavements constructed on them. Many researchers are doing extensive studies on this problem and its remedial measures. Among various methods for the solutions to the problems posed by expansive soils, the stabilization of such soils is the best practical option. In general soil stabilization seems to be an effective alternative for improving soil properties. Stabilization is a technique introduced many years ago with the main purpose to render the soils capable of meeting the requirements of the specific engineering projects. Stabilized materials may be used as improved sub grades or capping layers or sub-bases for road or airfield pavements. It is the alteration of one or more soil properties, by mechanical or chemical means, to create an improved soil material possessing the desired engineering properties. Soils may be stabilized to increase strength and durability or to prevent erosion and dust generation. Purpose of the stabilization of flexible pavement resting on weak and troublesome soil is to acquire desirable properties of sub grade which are high compressive and shear strength, permanency of strength under all weather and loading conditions, ease and permanency of compaction, ease of, drainage and low susceptibility to volume changes and frost action. Since sub grade soils vary considerably, the interrelationship of texture, density, moisture content and strength of sub grade materials is complex.

https://www.google.co.in/imgres?imgurl=https%3A%2F%2Fimage.slidesharecdn.com%2Ftayabji-160225025858%2F95%2Fsubgrade-stabilization-materials-methods-1-638.jpg%3Fcb%3D1456370808&imgrefurl=https%3A%2F%2Fwww.slideshare.net%2Fjillthepill81%2Feuropean-paving-practices-and-designs&docid=8fUNwAfmZx2dzM&tbnid=fP1OrOMFhhBWRM%3A&vet=10ahUKEwihjb21wM3aAhXJsY8KHchiBvAQMwhlKCAwIA..i&w=638&h=479&bih=557&biw=1242&q=mage%20of%20stabilise%20pavement&ved=0ahUKEwihjb21wM3aAhXJsY8KHchiBvAQMwhlKCAwIA&iact=mrc&uact=8

Thank you Nasir and prem

My earlier answer is for urban pavements and the solutions suggested are working well in my country. For asphalt roads and highways I would go for Brem Baboo explanations and suggestions.

Hello Debojit Sarker

From your experimental tests you discovered that " there is a increasing trend of swelling index if percentage of fly ash is increased from 5 to 20%." This is an indication that fly ash cannot stabilize an expansive soil. Similarly, cement cannot do the same. The solution for an expansive soil is to introduce a geomembrane at the interface between pavement and subgrade to prevent ingress of water into the subgrade. In addition, drainage should be provided to conduct storm runoff to a diversion point. The road shoulders should also be protected with a geomembrane below them. The difference between geomembrane and geotextile should be noted.

Amaechi answer technically support the different practices that try to prevent water to reach subgrade for urban pavements areas laid over expansive soils. In my earlier answer I have mentioned our local practice in areas dominated by expansive soils. In this regard would Amaechi and other involved researchers elaborate on the kinds of geomembranes that could be introduced in this case.

Three kinds of geomembranes which are commonly used for waterproofing are (1)constituted by plasticized poly vinyl chloride (PVC-P), (2) high density polyethylene (HDPE) and (3) terpolymer rubber of ethylene-propylene-dienic monomer (EPDM). All of these have comparable qualities and can serve beyond 15 years in reservoir and waste containment applications. The choice of which to use should depend on cheapness in the local market.

Hi Amaechi, absolutely useful information, many thanks

Dear, the best stabilizing agent for expansive soil is hydrated lime.

Many techiques can be used for stabilization of expansive soils. Using various additives such as lime, cement, fly ash, industrial waste products and ‎Polymer. it is recommended to use local available materials and low cost. ‎