Soil Stabilization

Soil stabilization is treating the subgrade material or subbase of a road so that it’s properties are improved. The improved properties are the ones we talked about in the previous section, ground improvement. The difference between soil stabilization and ground improvement is that soil stabilization deals with only improving characteristics of a subbase that will be placed under a road, or the subgrade material under the paving and subbase layers of a road or a paved area. Ground improvement however, is improving the earth below the structures, it can go much deeper depths. So these two terms are not so distant but the distinction should be known.

Soil stabilization methods basically fall into two broad categories, such as, compaction and mixing. Mixing methods can be grouped as mechanical and additive.

Mechanical mixing method means, blending soils of two or more gradations (grain sizes), to meet a required specification. A soil mixture made of different gradations is a better graded soil as the small particles can fill the voids between larger particles. Indeed, in soil mechanics, the presence of similar proportions of different sized particles is called a well graded soil. (But for a geologist for example, on the contrary, a well graded soil means a soil of uniform size).

Additive method means, improving properties of the soil by adding certain manufactured additives and mixing them with the soil. These materials can be portland cement, lime, fly ash, bitumen, and several more, either used alone or as a mix. Each additive is better suited for different purposes and for different type of soil.

After mixing the soil by either mechanical or additive methods, the mix is spread and compacted at the construction area. Sometimes, without mixing, only compaction is performed.

Sometimes, in addition to methods described above, geosynthetics can also be used for soil stabilization. This is called soil reinforcing, which we had mentioned in previous section and will further discuss under the section for retaining walls, which is the next section.

In the next post of this series, we will discuss “Retaining Structures” Go back to Index Page

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