Soil stabilization of highway embankment
• Mechanical stabilization: Improvement of soil properties can be achieved by changing particle gradation. The engineering performance depends
mainly on grain size distribution and plasticity.
Significant changes in the properties can be made by the addition or removal of suitable soil fractions.
Granular fraction imparts strength and hardness. Fine fraction imparts cohesion, water, retention capacity and it acts as filler.
• Extreme caution is required for adding fine to roadbases and subgrades.
• The common technique of soil alteration is the addition of sodium montmorillonite (bentonite) to reduce the permeability of the soil. Addition of 10% of
bentonite reduces permeability coefficient k. Asphalt
have been also tried.
Lime Stabilization :
Hydrated (or slacked) lime is very effective in
treating heavy plastic clayey soils. Lime may be used alone or in combination with cement, bitumen, or flash. Lime has been mainly used for stabilizing the
road bases and subgrades.
• On addition of lime to the soil, two main types of
chemical reactions occur i) alteration in the nature of the adsorbed layer through base exchange phenomenon and ii) cementing or pozzolanic action.
Lime reduces P.I. of highly plastic soils making them more friable and easy to be handled and pulverized.
The P.I. of low plasticity generally increases. There is generally an increase in the O.M.C. and decrease in the compacted density, by strength and durability
• Normally 2 10 8 % of lime may be required for coarse-grained soils and 5 to IO % for plastic soil.
Cement Stabilization :
The soil stabilized with cement (Portland) is known as soil cement. The cementing action is believed to be the result of chemical reactions of cement with silicious soil during hydration. The binding action of individual
particles through cement may be possible only in coarse-grained soils. In cohesive soils, only some of the particles can be excepted to have cement bonds and the rest will be bonded through natural cohesion.
Bitumen Stabilization :
• Earth roads can be improved by spraying the dry soil surface with a stabilizer such as aspheric and cut back bitumen oil, tars, or emulsions in small quantities. The bituminous materials when added to soil impact cohesion or binding action and reduce water absorption. About 4 to 7 % by weight of
bitumen is required. Any inorganic soil can be
stabilized well-graded soils give goods results from 10^3 mm/s to 10^8 mm/s in case of silty sands. Local clays may be used.
These are the methods of stabilization