Vane shear testing in Peat 1

[antonista]

Anybody know the definitive correction factor to apply to the shear vane test when performed in peat?

The "Muskeg Engineering Handbook", 1969, gives a calculation which results in a value only 25% of the value given in ASTM D 2573-01. Is this to account for the overestimation from the test in peat, or is it just an old, outdated formula?

Also, anybody know of propper correction factors for different sized vanes?

 

[jdmm]

You might want to ask the question 'what are we testing when we do a vane shear test in peat'. Remember that you are testing organic material and not mineral soil. If you happen to shear through a root you might get a vane strength many times the bulk strength of the peat. My suggestion is to use the vane only as an 'indication' of the shearing resistance of the peat.

 

[coneboy]

Many times in the past I have had discussions with clients regarding the high vane test values we recorded in peats. Based on my experience the organic fibers just wrap around the vane blades. For this reason most of the Geotech cosultants I know don't do peat vane tests anymore.

The shear vane does work quite nicely in the organic silts which typically underlye peat deposits.

coneboy

 

[Llessur]

I agree whole-heartedly with the above.

Recently spent/wasted two whole days grappling with shear vanes in peat and most, if not all of my results were 'interestingly' high.

In my opinion, the time spent trying to get half-decent results from this process far outweighs any benefits gained from it.

Good luck though!

 

[AZdinak]

In a sarcastic voice, complete a random variable study. Completing FVS in peat is risky business and is hit or miss. Unfortunately, you won't know whether you have a hit or miss. Also watch out for shells in soft marine clays, they can often skew results to the point of chaos. Zdinak

 

[msk1529]

i need some typical vane shear test results for different kinds of soils.any help will be appreciated.

 

[BigH]

Good advice about vane testing in peat - if you have fibrous peat. But, as you will note in the Muskeg Engineering Handbook, there is also a variety of peat that is amorphous - non-fibrous. In these deposits, the vane shear tests would be suitable. As with any field test, there are factors that can skew the results (e.g., a cobble in a sandy deposit). I would look up in the literature other than just the MEH; there is a lot of information out there. Also, you might check with some of the Canadian Geotechnical firms - the ones that do a lot of work in Northern Ontario; they might be willing to part with some advice.

 

[cbosy]

There is an excellent paper written by Edil and Wang (ASTM STP 1374) that came up with a Cu/Effective stress=.59 for peat which is what I use when designing surcharges and it seems to work.