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Leda Clay

Leda Clay

Leda Clay

(OP)
What exactly is Leda Clay and how does one deal with it? Someone asked me recently and after searching the web I discovered that it appears to have a low remoulded strength and will liquify if touched.

It it normally removed, avoided or strengthened. This is a general interest question.

Thnaks

newbuilder

RE: Leda Clay

Leda clay is a soft clay, with a typical characteristics of varving (layered), high sensitivity (high ratio between peak and remolded strength), and it is usually associated with sediments which were deposited during the inundation of the glacial lakes in the prehistoric time.  In some location in Canada, it has been associated with champlain or marine clays (eastern province), Leda clay (northern Ontario/Quebec areas), Lake Aggasiz clay (Winnipeg/Manitoba).

Because of the structure of the clay, in which upon disturbance it will loss its strength, lanslides occur in the areas which have this type of clay. There are lots of technical articles which were written over the years in Canadian Geotechnical Journals. Famous Canadian landslide failures, such as in Breckenridge Creek, Rockcliffe on Ottawa River, Orleans in Ontario, St. Jean - Vinney, toulnustouc river in Quebec, etc were associated with this type of soft clay.

You will see that highway cut or embankments in these areas have been cut or constructed with very flat slopes, such as 6H:1V of flatter. This is because in long term stability analysis, the remolded strength will govern, as the structure of the original clay will breakdown from disturbance, groundwater flow, loadings, etc.

Hope that this will give some insight about Leda clay.

RE: Leda Clay

(OP)
Yes, thank you.

RE: Leda Clay

Field vane testing with an accurate vane unit and experienced staff will show the dramatic difference between the peak and remolded strengths of these clays.

An electronic cone test might be more economical and would also show the difference in peak and remolded strengths.  
Comparing the interpreted soil strength values to those of the friction sleeve will provide a good estimate of the sensitivity.

I would not recomend SPT testing for these types of soils as you will require a level of accuracy that the SPT can not provide.

Best of luck
Coneboy

RE: Leda Clay

Hi,

I am thinking of building a house on a lot of 3 acres.  Only 0.75 acres (flat part of lot) has been designated by an engineer as buildable because most of the 3 acres is leda clay.  Is it safe to build a house on leda clay even in flat areas?  Thank you.  

RE: Leda Clay

I am not sure of how sensitive the clay in your area is, but there is an area in Maryland over the calvert formation which is a heavely over consolidated clay which has a tendency to loss strength when remolded.  We build have build plenty of residential home on it.  The soils have tremedous bearing capacity with little settlement.  I think the key is to brace all excavations and get the foundations in quickly without doing to much disturbance to the underling soils.

RE: Leda Clay

In Ottawa, Canada we routinely build on Leda clay for residential structures. Remember there should be no major fills on slopes and ensue proper drainage of cuts.  If you are dealing with a genuine Leda clay,it can flow like water once it becomes disturbed, so treat it with respect.

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