Smart questions
Smart answers
Smart people
Join Eng-Tips Forums

Member Login

Remember Me
Forgot Password?
Join Us!

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips now!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

Join Eng-Tips
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.
Jobs from Indeed

Link To This Forum!

Partner Button
Add Stickiness To Your Site By Linking To This Professionally Managed Technical Forum.
Just copy and paste the
code below into your site.

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...
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?


¡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.


¡papá gordo ain't no madre flaca!

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!

Back To Forum

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close