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Parisky (Geotechnical) (OP)
24 Mar 09 7:48
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 (Structural)
24 Mar 09 9:45
I'm not sure why you want a dynamic subgrade modulus...sounds like a static application.
Parisky (Geotechnical) (OP)
24 Mar 09 10:04
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 (Geotechnical)
24 Mar 09 11:08
Isn't low-strain shear modulus involved in this somehow?

f-d

¡papá gordo ain't no madre flaca!

Parisky (Geotechnical) (OP)
25 Mar 09 3:19
I am more interested in compression modulus and not shear modulus... I guess anyway
Ron (Structural)
25 Mar 09 6:21
How transient is the loading?  Where is the water table?

It might not react as a dynamic load.
ItsOnlyMud (Geotechnical)
7 Apr 09 9:25
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 (Civil/Environmental)
7 Apr 09 19:35
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 (Geotechnical)
7 Apr 09 22:31
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!

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