What is Soil Stabilization

Definition : The engineering properties of poor soils can be improved by the use of admixtures is known as soil
stabilization. In simple terms, the engineering properties of soil are modified to attain the more stable soil.

The stabilized soil may form the sub-grade or wearing layer of road.

Necessity of Soil Stabilization

• To alter the properties of soil to suit the traffic requirements.
• Generally to increase shear strength of soil.
• It is done to minimize the swelling due to wetting and shrinkage bearing.
• To increase bearing capacity of soil.
• It prevent the crack in soil due to reduction of moisture content.

Soil Stabilization Methods

Following are the methods of soil stabilization commonly used :

• Mechanical Stabilization.
• Bituminous Stabilization.
• Lime Stabilization.
• Cement Stabilization.
• Chemical Stabilization.
• Miscellaneous Methods of Stabilization.

1. Mechanical Stabilization :

This is the most commonly used method of soil stabilization. It is simple and economical. Following three cases will be considered for sand-clay road where mechanical stabilization is done.

Case 1 : Sandy soils i.e. when sand is present and clay is absent.
Case 2 : Clayey soils i.e. when clay is present and sand is absent.
Case 3 : Neither sand nor clay is present to a sufficient extent.

Case I : Sandy Soil :

When the sub-grade is sandy, the existing road surface is cleaned. It is shaped to require section. The top layer of sand of about 50 mm to 100 mm depth is removed.

It is stacked on the sides. The layer of selected clay is then spread upon the surface and it is again covered by the sand which was previously removed.

The two materials are mixed under optimum moisture condition by means of plough, burrows or blade graders.

Mixing of material is carried out till uniformity of texture and moisture are attained. Finally the compaction is done by medium roller of sheep foot roller.

Case II : Clayey Soils :

When the sub-grade contains a large amount of clay, the road surface is cleaned and it is shaped to the required section.

The top 50 mm to 100 mm thickness of clay is loosened or disturbed by means of a plough so that it contains cracks extending to a depth of about 70 mm to 100 mm.

The selected sand is spread and well mixed. Then compaction is carried out by sheep foot roller and then by medium roller.

Case III : Neither Sand Nor Clay is Present :

When the sub-grade does not contain sand or clay to considerable extent, materials (i.e. sand and clay) are brought to site and well mixed in required proportion.

The mixture is spread on road surface. Then compacted by sheep foot roller first and then by a medium roller.

In all above three cases, it should be seen that final section of the road surface has a camber of 1 in 24 to 1 in 36 to drain the surface water.

Factors Affecting on Mechanical Stabilization

The mechanical stability of mixed soil depends upon the following factors :

1. Gradation :

The gradation of the mixed soil should be such that the voids of the coarser particles are filled with finer particles so that a high density is obtained.

2. Compaction :

The mechanical stability of the stabilized soil mass depends upon the degree of compaction attained in the field. Normally, the compaction is done at or near the optimum water content.

3. Soil Properties :

Generally the soil containing higher liquid limit and plasticity index are suitable for use as soil binders for surfacing.

These type of soil generally possess greater cohesion and better moisture retention capacity. They provide a better seal against the downward movement of surface water.

4. Mechanical Strength of the Aggregate :

When the aggregates used have high strength the mixed soil attains higher stability.

However if the mixture is properly designed and compacted even the aggregates of relative low strength can provide good mechanical stability.

5. Mineral Composition :

The mechanical stability of the mixed soil is totally depended upon the composition of the minerals in it. Hence the minerals should be weather resistant.

2. Bituminous Stabilization :

In this method of soil stabilization, bituminous materials such as tar and asphalt are generally used. Bituminous stabilization generally enhances the stability of the soil and reduces its water absorption quality.

Due to this behavior the soil doesn’t get eroded easily and which keeps the surface intact for a longer time.

In this method the combinations of  soil, sand, oil etc are also used along with bitumen for greater results.

3. Lime-Soil Stabilization :

Lime or slaked lime is also one of the best option to be used for soil stabilization. This is one of the economical way of soil stabilization.

Generally a soil which is highly clayey and plastic in nature is stabilized by using slaked lime. As a result the strength and the durability of soil increases.

Whenever there is excess moisture in the soil, it is removed with the help of lime, as its one of the best water absorbing agent.

Slurry lime can also be used in dry soils conditions where water may be required to achieve effective compaction.

4. Cement-Soil Stabilization :

Cement is one of the oldest binding agent used for soil stabilization. Unlike other components, its reaction is not inter-related with the soil minerals.

Cement directly reacts with the water present in every soil to make the stabilization process effective.

There are many types of cement available in the market. The selection of the cement totally depends on the type of the soil and the purpose for which the stabilization is carried out.

5. Chemical Stabilization :

Chemical stabilization is one of the process in which different chemicals are added into soil to alter the properties of soil. This generally helps in proper soil stabilization.

Sodium and calcium chloride are among the most commonly used chemicals for soil stabilization. Soil stabilization depends mainly on chemical reactions between stabilizer and soil minerals to achieve the desired effect.

6. Miscellaneous Methods :

Despite from above mentioned soil stabilization methods, there are many other methods which are also sometimes used if the above methods doesn’t get applied to the scenario.

Following are the other methods of soil stabilization :

• Mass Stabilization Method
• Deep Mixing Method
• Grouting Method
• Electrical Method