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Kamis, 25 November 2010

Menard Pressure Meter for Young Modulus

Jordan2 (Geotechnical)
21 Jun 06 11:34
Hi,
it is not clear to me why it is suggested to derive the Young modulus (Ey) from the pressumeter (Menard) modulus (Em) by dividing the latter by one reological coefficient (alfa). My question arises from the fact that Em is already calculated considering only the elastic deformation occurred during the pressumeter test.
I imagine that a correction could be required for different stress path, but why a reological factor is involved?
Thank you for your comments

mdhshanwil (Geotechnical)
21 Jun 06 15:59
Hi Jordan2--

I believe the alpha factor you are describing is a combination of three effects that combine to force an adjustment to obtain an elastic modulus from the PMT modulus. The first is stress path, as you mentioned. The second is that the PMT modulus is somewhere between a compressive modulus and a tensile modulus. The third effect is due to the strain levels over which the PMT test is measured.

There is a lengthy discussion of this in Baguelin's (1978) book on the PMT in Chapter 6.



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Jordan2 (Geotechnical)
22 Jun 06 6:08
Thank you Mdhshanwil,
I agree with your evaluation. My curiosity was mainly oriented to the fact that the term "reological" was involved in the correction factor: in my opinion this choice is not so logical..
Kind Regards



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casimmons (Geotechnical)
23 Jun 06 12:42
The alpha factor considers that the PMT is done in the horizontal direction, and for settlement calculations you are interested in the vertical direction. It also considers affects such as aging, overconsolidation, soil type, etc. Obviously selection of the appropriate alpha factor is very important.



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BigHarvey (Geotechnical)
26 Jun 06 2:52
The rheological coefficient alpha was created by Louis Menard to allow theory to match to practice. A pressuremeter modulus is not exactly a Young's modulus. You need this coefficient to calculate settlements. however be careful when calculating settlements for soft clays where the behaviour is more consolidation than elasticity : in this case you will be more accurate by using a oedometric approach.

BigH (Geotechnical)
26 Jun 06 4:52
BigHarvey - good point; and one to mirror why you would't use a normal plate load test result for settlement either!

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