Shrink Swell Clays & Lime Stabilization

[MasterONone]

I have a known high shrink swell clay that I am investigating stabilizing with lime for road and structural building pad construction. The properties of the existing soil are as follows:

% Passing No. 200 Sieve = 78%
Liquid Limit = 45
Plastic Limit = 22
Plasticity Index = 23

With the addition of 5% quick lime, according to ASTM D 6276-99a "Standard Test Method for Using pH to Estimate the Soil-Lime Proportion Requirement for Soil Stabilization", the properties of the "Stabilized" soil is as follows:

Liquid Limit = 63
Plastic Limit = 46
Plasticity Index = 17

Note that the addition of lime for the stabilization decreased the PI to below 20, which is a local standard. But increased both the liquid and plastic limits, with the liquid limits well over the local standard of 40.

Q. Can this increase in LL and PL be detrimental, besides where it falls on the Plasticity Chart?

 

[GeoPaveTraffic]

Are you adding the lime by volume or weight?

I have never used the ASTM to determine the amount of lime to add, however, common practice in the St. Louis area would be 3 to 5 percent by volume for a clay like you have. The material would be dry mixed with the soil and imeadiately compacted. Desity tests will likely be performed, though they have very little meaning on the modified soil. Acceptance would be based on the undrained strength of the material after a few hours or the next day.

I do not believe that LL, PL, and PI have much meaning for a soil that has been modified with a significant amount of lime. However, any amount of lime only works if it is very well mixed into the soil. Having original soil clumps with lime around the edges does little to reduce the shrink/swell.

 

[dmoler]

Larger gain in moisture content for the LL than I am used to seeing. Usually the reduction in PI comes from substantial increase in the PL, with a little movement for the LL value. The high LL and PL values would not be detrimental, since the soil is modified, and the water is 'bound' in the chemical reaction, and in this case the PL/LL/PI are not a measure of the expansiveness.

For roadways, I used to run a series of 0,2,4,6,8,10% lime content atterberg limits on the clays. The soil would be stabilized at the percentage where the PI becomes constant. Very little change in the PI would happen with addition of extra lime (for these low lime percentage ranges). All percentages based on weight.