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What is Soil Stabilization?

Cement soil stabilization is used to ensure adequate sub-grade stability, especially in weaker and wetter soils. By reducing the damaging effect of excessive moisture content and the moisture sensitivity of the soil, it is able to remain stable and capable of carrying increasing traffic volumes and heavier loads.

This process is used in areas where weak sub-grade soil exists and where expansive soils are encountered. It is especially good in places that receive heavy rain and snow amounts and have high ground water tables that can weaken the sub-base as they are pulled to surface. It also keeps the soil’s properties even through the freezing/thawing cycles.

Cement modified soil is a soil that has been treated with a relatively low proportion of Portland cement. The objective of cement soil stabilization is the change the makeup of the soil so it is more suitable for construction. The improvements to the soil that occur when using this process is preformed are:

1) Soils plasticity index can be reduced. (The amount of water the soil can absorb) It creates a greater resistance to keeping water out.

2) Soils bearing ratio is increased.

3) The material shearing strength can be increased. This will provide uniform strength across the area by dispersing the load over a greater area.

4) Shrinkage or swelling characteristics for the soil can be decreased.

5) The amount of fine-grained material particles (silt and clay) can be reduced.

Cement soil stabilization is used to ensure adequate sub-grade stability, especially in weaker and wetter soils. By reducing the damaging effect of excessive moisture content and the moisture sensitivity of the soil, it is able to remain stable and capable of carrying increasing traffic volumes and heavier loads.

This process is used in areas where weak sub-grade soil exists and where expansive soils are encountered. It is especially good in places that receive heavy rain and snow amounts and have high ground water tables that can weaken the sub-base as they are pulled to surface. It also keeps the soil’s properties even through the freezing/thawing cycles.

Cement modified soil is a soil that has been treated with a relatively low proportion of Portland cement. The objective of cement soil stabilization is the change the makeup of the soil so it is more suitable for construction. The improvements to the soil that occur when using this process is preformed are:

1) Soils plasticity index can be reduced. (The amount of water the soil can absorb) It creates a greater resistance to keeping water out.

2) Soils bearing ratio is increased.

3) The material shearing strength can be increased. This will provide uniform strength across the area by dispersing the load over a greater area.

4) Shrinkage or swelling characteristics for the soil can be decreased.

5) The amount of fine-grained material particles (silt and clay) can be reduced.

The Process

Before stabilization can begin the area is brought to grade as shown on the plans and a Plasticity Index test is performed. The application we do is called cement-treated soil which is when aggregate material and/or granular soils are mixed with measured amounts of Portland cement and water, then mixed and cured to form a durable sub-base material.

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The process begins by spreading cement over the area to be stabilized at the proper percentage as established by the plasticity index test. As an example the soil in the Bakken region requires seven percent.  Then using a Cat soil stabilizer, the cement is mixed into the area at a one foot depth.  Following behind the stabilizer the soil is compacted with a sheep’s foot roller. After this has been done the area is watered as needed to get the proper moisture content.  The next step is to rerun the stabilizer and remix the area again and then compact it for the second time.

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Once this is complete the area is re-graded using a laser system tied into the controls of the grader to ensure perfect elevations and grades per plan.  The last stage in the process is to once again compact it and then seal the area with a smooth drum roller.  The area is then watered again for optimum moisture.  Now gravel/scoria can be placed and it will remain because the sub-base is now resistant to water, has a higher bearing strength and will hold up under freezing/thawing conditions.

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Advantages and Longevity

The most important advantage to utilizing soil stabilization is saving money.  Stabilization helps in eliminating problems with pads base failure and the cost involved in maintaining the life of the pad.  This is achieved by:

  1. Higher resistance values
  2. Reduction in plasticity index
  3. Permeability is lowered
  4. A reduction of pavement thickness
  5. Excavation of unsuitable material and new material brought in is eliminated.
Life expectancy for subgrade stabilization is more than twenty years thus eliminating the need to rebuild pads.