206 Lime Stabilized Subgrade

Specification Changes

Uses and Application for Lime Stabilized Subgrade

Materials (206.02)

Limitations, Test Rolling and Spreading (206.03)

Mixing (206.04)

Compaction (206.05)

Contractor Designed Lime Soil (206.06 & 205.07)

Specification Changes

  1. Added PN-206 Test Rolling.
  2. The construction procedures were slightly modified.
  3. The stability issue was referred to the Earthwork Construction Manual.
  4. Drainage and maintenance work done according to 203.04.A.
  5. The language in 206 was shortened by referring to 205.
  6. Prime coat is used for curing not water.
  7. Only specify water when the slurry method is specified.
  8. Used for A-7-6 and A-6-b soils with a PI> 20.

Uses and Application for Lime Stabilized Subgrade

  1. Lime is most effective in treating soils with a PI>20.
    1. A-7-6 and A-6-b’s soils.
    2. Use for continuous sections greater than 20,000 square yards.
  2. Lime Stabilized Subgrade is used to modify the subgrade to bridge soft areas.
    1. See Figure 204.H Subgrade Treatment Chart and the other pertinent sections.
    2. Use average N values as low as 10, average U of 1.0 tons/ ft2 and to remove ruts < 6 inches (150mm).

A brief outline of the specification requirements follows:

Materials (206.02)

  1. Use hydrated or quick lime according to 712.04.B. 
    1. 100% of the quick lime must pass the # 4 sieve.
    2. Use between 4 to 8 % by weight.
    3. Plan will include 5 % Hydrated.

                                                               i.      If quick lime is used

1.      Use 4 %

2.      Use the conversion in 205.08 for payment

  1. Soil must weight at least 100 lb/ft3.  
  2. Use Prime coat for curing at 0.3 gallons per square yard.
    1. Do not use the type specified in the spec book.
    2. It can leach out during a rain.
    3. Use 702.04 Emulsified Asphalt Type RS-1 or RS-2.

Limitations, Test Rolling and Spreading (206.03)

  1. Limitations are the same as in 205.03.
    1. Temperatures greater than  > 40o.
    2. Material not Frozen.
    3. No Severe Wet Conditions.
  2. If stabilization specified in spot locations.
    1. Test roll to locate soft areas with grader.
    2. Investigate if rutting is greater than 4”.
  3. If stabilization is specified throughout the project
    1. Proof Roll after stabilization.
  4. See Subgrade Stabilization Sections in this manual.

Spreading

Usually use 5 percent lime per 110 pound soil.  To calculate the number of pounds of lime to use per square yard, use Equation 205.2:

Equation 206.1 – Pounds of Lime per Square Yard

where:

9 ft2  in a square yard

9 ft2 /yd2 x (one inch deep)/12 inches/ft = ¾ ft3/yd2 per one inch deep

D = depth (inches)

WD = average density (lb/ft3)

% = percent lime (expressed as a decimal)

 

For example, if using 5 % lime, 110 lb/ft3 material, at 12 inch lifts:

¾ X 12 inches X 110 lb/ft3 material X 0.05 = 49 lb/yd2 of lime

Use a square yard canvas to weight the lime once the pounds per square yards have been determined.   Once you determine the amount is correct, then you may want to just measure the thickness of the lime.  The Contractor must submit a spreading plan to obtain the correct amount of lime per square yard.

See the re-agitation requirement for the slurry method.  Use the slurry within 24 hours of mixing to maximize the effectiveness.

Mixing (206.04)

  1. For Slurry Method.
    1. Open the soil up prior to applying the lime.
  2. Apply the lime and mix into the soil.
    1. Use a power driven mixer.
    2. During initial mixing.

                                                               i.      All clods less than 2 inches (50mm).

                                                             ii.      Depth 9 to 16 inches.

  1. Add water.
    1. Optimum for hydrated.
    2. + 3 % for quick.

                                                               i.      Prevents expansion.

  1. Lightly compact.
  2. Cure with Water for 24 Hours to 7 days.
    1. Mellows the soil.
  3. Re-Mix the Soil.
    1. Soil 100 % < 1” and 60 % P- #4 Sieve.
    2. Add water to the same moisture contents.
    3. Check soil for uniform color.

Compaction (206.05)

  1. Compact to 98% of the maximum density.
  2. Use the one point proctor method in Supplement 1015.
  3. Measure the density and take the proctor soil from under the gauge.
  4. Use the Ohio Typical Density Curves to pick the maximum density.
  5. In some rare cases, a test section may be constructed or the curves developed in section 205.07 and 206.06 may be used.
  6. Check the depth of the stabilization by:
    1. Digging a hole.
    2. Add Phenolphthalein to the sidewalls.

                                                               i.      Should turn purple.

    1. Can use diluted Hydrochloric acid.

                                                               i.      Should fizz.

  1. Cure the Lime for 5 days.
    1. Make sure the surface is wet prior to adding prime.
    2. Will prevent drying of surface.
  2. Fine grading.
    1. New spec will require fine grading after curing
    2. Construct the grade an inch high and
    3. Take off an inch during fine grading.
    4. Top inch material can dry out during cure.

Contractor Designed Lime Soil (206.06 & 205.07)

Use this section to verify that the soil will increase in strength when the lime is added to the soil.

Unconfined strengths are determined to detail the strength gain.  This information can be used to make field adjustments if problems develop in the field.  Normal increases in strength range from 20 psi to 100 psi for Ohio soils.  Consider adding the durability test for cement to this work to ensure durability.