soil stabilization

Introduction
Soil stabilization refers to the process of changing soil
properties to improve strength and durability. There are many
techniques for soil stabilization, including compaction,
dewatering and by adding material to the soil. This summary
will focus on mechanical and chemical stabilization based
adding IRC materials. Mechanical stabilization improves soil
properties by mixing other soil materials with the target soil
to change the gradation and therefore change the engineering
properties. Chemical stabilization used the addition of
cementitious or pozzolanic materials to improve the soil
properties. Chemical stabilization has traditionally relied on
Portland cement and lime for chemical stabilization. There a
number of IRC materials that can be used individually, or
mixed with other materials, to achieve soil stabilization.
IRC Materials in Soil Stabilization Applications
Coal fly ash (CFA) has a long history of use in soil stabilization applications. Class F CFA is typically
added to both cement and lime stabilized soils because the pozzolanic reactions provide improved
strength and increased density and durability. In addition, self-cementing (Class C) CFA has been used
successfully to stabilize fined grained soils. It was found that the rapid reactions of the Class C CFA
reduced the plasticity of the soil, lowered the water content and increased the strength of the soil.
Similarly, blast furnace slag in the form of slag cement has also been used successfully for soil
stabilization. Slag cement can be used by itself or mixed with Portland cement, depending on the site
conditions. Slag cement is a cost effective way to dewater the soil and increases the strength. In addition,
work has shown that soil cement can help mitigate sulfate-induced heave than is often encountered
during lime stabilization of sulfate bearing soils.
It should be noted that the performance of CFA and slag cement in soil stabilization applications, like that
of lime and cement, is very dependent on the site conditions. The fines content and plasticity of the soil,
the presence of sulfates, depth to the water table and freeze-thaw conditions are all factors that need to
be considered when stabilizing soil. Test mixture should be made to determine the best mixture for the
site.
Foundry sand has also been shown to be an effective soil stabilization material when added to poor soils
to change the gradation. The foundry sand improves drainage, which leads to better engineering
performance.
Benefits
The use of coal fly ash, slag cement and foundry sand for soil
stabilization provides cost effective methods to improve the
engineering properties of marginal or problematic soils. Soils
stabilized with these materials have been extensively tested
and do not have any adverse environmental impact. In fact,
there is actually an added environmental benefit of reducing
green house gas emissions and energy consumption by using
less energy intensive materials like lime and cement, and by
reducing landfilling of high quality foundry sands.