Chapter 15 Soil Stabilization
STABILIZATION OF SOILS
Stabilization is the process by which the strength and stability of a soil mass is improved and increased
Soil Stabilization Methods with Different Materials:
Following are the various soil stabilization methods and materials:
-Soil Stabilization with Cement:
The soil stabilized with cement is known as soil cement. The cementing action is believed to be the result of chemical reactions of cement with siliceous soil during hydration reaction. The important factors affecting the soil-cement are nature of soil content, conditions of mixing, compaction, curing and admixtures used.
The appropriate amounts of cement needed for different types of soils may be as follows:
Gravels – 5 to 10%
Sands – 7 to 12%
Silts – 12 to 15%, and
Clays – 12 – 20%
Soil Stabilization using Lime:
-Slaked lime is very effective in treating heavy plastic clayey soils. Lime may be used alone or in combination with cement, bitumen or fly ash. Sandy soils can also be stabilized with these combinations. Lime has been mainly used for stabilizing the road bases and the subgrade.
-Lime changes the nature of the adsorbed layer and provides pozzolanic action. Plasticity index of highly plastic soils are reduced by the addition of lime with soil. There is an increase in the optimum water content and a decrease in the maximum compacted density and he strength and durability of soil increases.
Normally 2 to 8% of lime may be required for coarse grained soils and 5 to 8% of lime may be required for plastic soils. The amount of fly ash as admixture may vary from 8 to 20% of the weight of the soil.
Soil Stabilization with Bitumen
Asphalts and tars are bituminous materials which are used for stabilization of soil, generally for pavement construction. Bituminous materials when added to a soil, it imparts both cohesion and reduced water absorption. Depending upon the above actions and the nature of soils, bitumen stabilization is classified in following four types:
Sand bitumen stabilization
Soil Bitumen stabilization
Water proofed mechanical stabilization, and
Chemical Stabilization of Soil
-Calcium chloride being hygroscopic and deliquescent is used as a water retentive additive in mechanically stabilized soil bases and surfacing. The vapor pressure gets lowered, surface tension increases and rate of evaporation decreases. The freezing point of pure water gets lowered and it results in prevention or reduction of frost heave.
-The depressing the electric double layer, the salt reduces the water pick up and thus the loss of strength of fine grained soils. Calcium chloride acts as a soil flocculent and facilitates compaction.
-Frequent application of calcium chloride may be necessary to make up for the loss of chemical by leaching action. For the salt to be effective, the relative humidity of the atmosphere should be above 30%.
-Sodium chloride is the other chemical that can be used for this purpose with a stabilizing action similar to that of calcium chloride.
-Sodium silicate is yet another chemical used for this purpose in combination with other chemicals such as calcium chloride, polymers, chrome lignin, alkyl chlorosilanes, siliconites, amines and quarternary ammonium salts, sodium hexametaphosphate, phosphoric acid combined with a wetting agent.
Test on Expansive Soil:
-FREE SWELL TEST
-DIFFERENTIAL FREE SOIL TEST
|Degree of Expansiveness||% DFS|
|Medium||20 to 35%|
|High||35 to 50%|
|Very High||> 50%|
|Plasticity Index||Swelling Potential|
|0 to 15||low|
|10 to 35||medium|
|20 to 40||high|
|> 35||very high|