Soil Modification is sometimes referred to as "mud drying;" however, soil modification can result in other significant improvements in soil properties as well. Often, subgrade soils are too wet, exhibiting poor workability and lacking sufficient strength to support construction equipment. Chemical additives such as lime, fly ash, and cement can be added to these soils to dry and improve the workability of the soil.
Soil modification refers to the process of adding and mixing the above chemical agents into the soil to not only dry the soil, improving workability, but also reducing the plasticity index (PI) and shrink swell potential. These improvements often result in a slight increase in the shear strength of the soil.
There are two types of Soil Stabilization, chemical and bituminous. Chemical stabilization is the process of adding and mixing additional amounts of the same chemical agents used in soil modification into the soil to allow a significant increase in strength of the soil, thus improving the load bearing capacity of a sub-grade to support pavements and foundations. Soil stabilization results in the same improvements in soil properties that are achied with soil modification. Bituminous soil stabilization results in an improvement is soil strength but is not generally recommended for clay soils; therefore, is not used to modify soils. Many agencies require a specified increase in unconfined compressive strength before a soil can be considered a stabilized layer.
- 20 to 40% cost savings compared to removal and replacement.
- Reduction in Trucking of Material.
- 100% Reuse of subgrade materials for In-place Projects.
- Same day return to light traffic for some processes
- Up to 25 years of life extension. The limiting factor for service life of soil modified/stabilized pavements is typically the service life of the surface course and not the modified/stabilized mixture itself.
- Structural Layer (a) Coefficients of soil stabilized layers depends on the stabilizing agent used and vary from 0.08-0.15.
Issues Addressed
Soil Modification/Stabilization:
- Existing pavement failures due to weak unstable subgrades
- Weak or unstable subgrades for new consteuction
- Unsuitable subgrades due to high shrink/swell potential
- Unsuitable subgrades due to excessive moisture
Attributes
Soil Modification
- Reduction in plasticity and shrink/swell potential
- Reduce costs of undercuts, elimination of excavation and replacement of material
- Provides access onto and within project sites during all weather conditions
- Utilize onsite materials
Soil Stabilization (in addition to the above Attribites)
- Increases the structural integrity of the subgrade materials
- Can reduce the required thickness of the pavement section
- When performed on existing pavements, soil stabilization has many of the same attributes as base stabilization and FDR
Common Combinations
Soil Modification/Stabilization + FDR
Soil Modification/Stabilization + CCPR
Soil Modification/Stabilization + CIR
Soil Modification/Stabilization + any pavement section