Undrained Shear Strength of Compacted Clay

[jxzohio]

The clay fill will be placed in 8-inch-thick lifts and compacted to 95% of the maximum dry density per Standard Proctor method. The borrowed clay material (non-organic) has medium plasticity (LL between 30 and 50). What would be the undrained shear strength (range) from this compaction? Is there any literature related to this aspect? Thanks.

 

[fndn]

Your best and most accurate way would be to perform a triaxial test at the in-situ field density and directly obtain your cohesion value. Most of the litterature information has large scatter on the data points.

"An Introduction to Geotechnical Engineering" and "Soil Mechanics in Engineering Practice-3rd Edition" have such information.

 

[GeoPaveTraffic]

There is some literature on this, most of it had to due with the construction of earth dams. I have a copy... somewhere. I will try to look for it this comming weekend.

Not much need for it now working for the City.

 

[jxzohio]

GeoPaveTraffic,

Please help me have a look at your reference and let me know. I have a sheet pile wall to install which needs removal of extremely soft subgrade and replace it with compacted clay. I agree with fndn that I will also need to do a UU triaxial test on the compacted clay to confirm the assumed Su. Thanks for your advice.

 

[BigH]

The sort of bible reference, I believe, is the 1960 Boulder Conference on Clays (ASCE). Might try to find a copy of it and read the paper by, again, I believe, Bishop.
One caution on compacted clay fills - need to keep your lifts proper. I know one job that had major problems in tha the upper part of the lift was compacted and the lower part not nearly enough. After construction distress, they found this clearly evident by moisture content profile and undrained shear strength profile.
I would also surmise that the methods of compaction are very important as well. Use of sheepsfoot roller or PTR rather than vibratory. In the lab, things always are "ideal" in that the sample before compaction would be of similar gross gradation (i.e., clump gradation) but on the job site, clay borrow usually comes in much bigger clumps. If there is no care in breaking down the clumps before compaction, you might only pack the clumps together in a non-homogeneous mixture. The interconnected voids would have effects on the permeability of the fill mass as well on the strength of the mass.
Just some initial thoughts.