Soil Stabilization & Soil Modification

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Soil Modification and Soil Stabilization are similar processes that uniformly mixes chemical or bituminous agents into a soil to improve the workability and physical properties of the soil and possibly increase the strength and load-bearing capacity of the soil. With chemical agents such as lime, type C fly ash and cement, stabilization is achieved by adding additional amounts of the chemical, beyond that required for modification, to reach a specified increase in strength of the soil, producing a stabilized subgrade or foundation layer. Soil modification/stabilization can be used in new construction or reconstruction. Mixing of the modifying/stabilizing agent can take place at a central location or in-place. When mixed at a central location, a pugmill mixer is typically used to mix the modifying/stabilizing agent with the soil material and then the material is hauled to the site where it is placed and compacted. With in-place operations, the modifying/stabilizing agent is mixed into the existing subgrade. With reconstruction of an existing pavement, any existing materials above the subgrade are removed and subgrade is modified/stabilized in-place similar to base stabilization and FDR.


Equipment Variations


  • Onsite Soil Modification/Stabilization (New Construction): Modification/Stabilizing agent is added and the materials are mixed and compacted on site.
  • Reconstruction: The pavement section is removed down to the subgrade and the materials are either disposed of or hauled to a processing site for use as a stabilized base, FDR mixture or CCPR mixture. The exposed subgrade is then mixed with a modifying/stabilizing agent and compacted.
  • Central Plant Soil Modification/Stabilization: New or in-place soils are imported to a central location and stockpiled for future use. The materials are mixed in a pugmill mixer. The pugmill mixer has a soil feed conveyor belt with a belt scale linked to a computerized liquid modifying/stabilizing agent, water and additive system that accurately meters the materials into the pugmill based on the weight of the soil. Dry modifying/stabilizing agents are typically transferred via silo augers or separate transfer devices tied to the belt scale. The materials are processed and hauled to the project for placement and compaction.
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Off Road Spreader


The equipment used to perform Soil Stabilization will vary from contractor to contractor, but no matter how configured, the equipment performs the same general steps. The equipment requirements for Soil Stabilization depend on the specifics of the project but generally consists some or all of the following:

  • Modern, high horsepower self-propelled reclaimer
  • Pugmill mixer for central plant applications
  • End or bottom dump haul trucks
  • Calibrated bulk spreader for dry modifying/stabilizing agents
  • Mixer and tanker for slurry application of modifying/stabilizing agents
  • Emulsion or hot asphalt tankers for bituminous stabilization
  • Computerized emulsified asphalt or foamed asphalt injection system on the reclaimer
  • Motor grader
  • Water truck with spray bar 
  • One or more compactors (pneumatic-tired, pad foot and/or double drum vibratory rollers)


Material Variations

Chemical Modification is achieved with the addition of lime (hydrated or quicklime), lime kiln dust (LKD), self-cementing class C fly ash, class F fly ash (when used in combination with other additives), cement,  cement kiln dust (CKD),  calcium chloride, magnesium chloride to the pulverized materials.

Chemical Stabilization is achieved by adding an additional amount of the above listed chemical modifying agents until a predetermined increase in unconfined compressive strength is achieved. 

Other Modification/Stabilization Agents There are many other agents that are used to modify or stabilize soils and these include enzymes, polymers and other proprietary products.

Bituminous Stabilization is accomplished with the addition of emulsified asphalt or foamed (expanded) asphalt to the pulverized materials and is generally applicable to non chhesive soils.


Common Combinations

Soil Modification/Stabilization + FDR: Soil modification or soil stabilization can be used with FDR to allow in-place rehabilitation of a pavement with deep subgrade or drainage issues. 

Soil Modification/Stabilization + Base Stabilization: Soil modification or soil stabilization can be used with base stabilization to allow in-place rehabilation of a pavement with deep subgrade or drainage issues. 

Soil Modification/Stabilization + CIR or CCPR: Soil modification or soil stabilization can be used with CIR or CCPR to allow in-place recycling of a full depth asphalt pavement with deep subgrade or drainage issues.

Soil Modification/Stabilization + Any Pavement Section: Soil modification or soil stabilization can be used with any new or reconstructed pavement section.