Dynamic soil subgrade modulus

[Parisky]

I'm designing a mat foundation for a petrochemical reactor. I need to determine the dynamic subgrade modulus so to estimate the stiffness of springs in a finite element model.
I have some cross-hole results. Does anyone have an idea how to correlate the compression modulus E of cross-holes to SPT results or Pressiometric results?
And, does anyone have a correlation factor or function between static and dynamic subgrade soil modulus?

PS: I appologize for any faults in technical term.. am in Paris...
thanks

 

[Ron]

I'm not sure why you want a dynamic subgrade modulus...sounds like a static application.

 

[Parisky]

the explosion in the reactor is a dynamic load with a Pressure-time triangular curve. That's why I need a dynamic subgrade modulus.
a colleague proposed Ed=3*Estatic... does anyone confirm this roughly?

the Crossholes modulus are approximately 150times higher than the static modulus....

 

[fattdad]

Isn't low-strain shear modulus involved in this somehow?

f-d

¡papá gordo ain’t no madre flaca!

 

[Parisky]

I am more interested in compression modulus and not shear modulus... I guess anyway

 

[Ron]

How transient is the loading? Where is the water table?

It might not react as a dynamic load.

 

[ItsOnlyMud]

You need some geophysics. A combined compression wave and shear wave (P and S) survey will get you (if you can provide bulk density) the dynamic shear modulus, which is a low strain shear modulus. From this you can calculate all sorts of dynmaic reactions, such as rocking spring stiffness etc.

 

[msucog]

i got shear wave to spt correlations for my local geology but that doesn't do you much good in paris. could estimate p-wave from s-wave...P:S of 2 for soil above water table, P:S of 2.3 for soil below water table and P:S of 1.8 for rock. or just say 2 for round figures. or you could have more geophysical work done to look at p-wave since it typically doesn't take that much money for such a survey (much cheaper than crosshole). if it were me and had cross hole shear wave data, i'd approximate p-wave values and perhaps figure it few ways to see which is more conservative (and use a value somewhere between conservative and average). if the boreholes are cased and still accessible, you could even realize some savings and check p-wave there.

 

[fattdad]

If you ultimatly need low-strain shear modulus, you can estimate the shear modulus and use 1/10 the value for low-strain conditions.

f-d

¡papá gordo ain’t no madre flaca!