Lime soil stabilization

Lime soil stabilization method is a unique technic to improve the strength of the soil in different projects such as road buildings. Briefly, adding lime increases the soil stability, bearing capacity and reduce its  permeability. The high efficiency of this method has been proven by many projects all over the world. It is noteworthy that lime soil stabilization is suitable for clayey soils and not for granular soil or sandy soil.

Chemical effect of adding lime

When lime is added a pozzolanic reaction occurs resulting in production of stable calcium silicate hydrates and calcium aluminate hydrates. If there is enough lime and proper PH, this pozzolanic reaction might last for a very long period of time to be 100 percent completed. This chemical reaction is accompanied with an exchange of ions between lime and soil resulting in plasticity index reduction. Consequently adding lime increase the stability of soil. To reach the maximum possible strength and to optimize this method, mixture must be designed based on codes and experience of experts.

General procedure of lime soil stabilization

After designing the optimized mixture, lime content is added in two steps. Adding lime can be carried out either with slurry or lime powder. Adding slurry is more effective to reach a more uniform mixture. In case of adding lime powder, water is sprayed on the soil to provide the optimized moisture for the mixing.  After first adding is finished, depending on the type of the soil and the plan, the mixture is left for a period of time (up to 5 days). Next the remaining clime content is added to the soil.  The final mixture is compacted by rollers and moisturized to reach its maximum dry density. As usual, the quality of the operation should be verified with sampling and in situ tests.

Curing and additive considerations

To reach the ultimate stability, the mixture must be cured in the first and second mixing stages. Temperature plays a crucial part in curing process. Water content is another important factor in curing. In some projects, to increase the strength of the mixture, additives such as Portland cement and fly ash are used. However additives are generally produced for soil improvement, but use of some chemical additives might have detrimental effects on swelling properties of the soil. So it is highly recommended to consult with experts to choose the right chemical additives.

 

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