Static shear modulus based on geophysical results 4

[pelelo]

Engineers,

I have Vs30 from the geophysical report. As you may know G = gamma x (Vs)2. It is my understanding that in this case G would be the dynamic shear modulus Gdyn.

I was wondering if there is an approach on how to determine the static shear modulus Gstat, based on the Gdyn or Vs30.

And if not, what would be the the approach?

Thanks,

 

[EireChch]

I have worked with geophysical data and have never seen it referred to as Gdym and Gstat.

Shear modulus, or any parameter measured by geophysical methods are small strain measurements. You need to adjust them to a strain rate that is applicable to your case. For pile foundations Polous and Badelow (2015) recommend multiplying your small strain shear modulus by 0.2 factor.

 

[HTURKAK]

I looked ( Recommendations on Piling (EA-Pfähle) by Deutsche Gesellschaft für Geotechnik e.V.)

Gstat is obtained from the hyperbolic function (Hyperbolic soil stress-strain relationship graphic )

But the following paper is worth to look .



Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[geotechguy1]

At what strain level would you like a G value? An initial tangent modulus? Secant modulus at some % change? A cyclic modulus after 1,000 cycles? A dynamic modulus for a single high-rate load?

It's a trick question, the number of answers is almost limitless depending on the conditions you are considering.

 

[ssiguy]

What you get from a geophysical survey such as MASW is the small strain shear modulus, Gdyn or G0. The static shear modulus, Gstat or Greduced, depends on the level of shear strain expected for you foundation/application. Shear modulus degrades as a function of shear strain and the type of soil. Expect to multiply G0 by a factor of 0.25 to 0.65 for most cases, unless unusually high shear strains are expected.

Jomaa Ben Hassine, PE
President
Civil Renewables, Inc.

http://www.civilrenewables.com

 

[pelelo]

Thanks ssiguy,

Just to clarify, when you say "Expect to multiply G0 by a factor of 0.25 to 0.65 for most cases", you meant to obtain Gstat from a G0?.

IF not, do you know if there is a reference that correlates Gdyn and Gstat? (if there is any)