Seismic bearing capacity & settlements

[Mccoy]

Colleagues,

sesmic behaviour of soil is presently a hot topic in Italy and Europe in general, as specific state codes and regulations are being issued on the wake of Eurocode7 and Eurocode8.

I was researching methods for seismic evaluation of bearing capacity and settlements, and the classic publication appears to be Richard, Elms and Budhu, 1993.

This is also reported on Das' "Shallow foundations".

Interestingly enough, settlements are calculated without the use of elastic modulus in the input.

Also, more method are available in the literature, some focusing on the loss of bearing capacity due to the inclination of load resultant during seismic events.

My question is:
has anyone of you guys any practical experience in the application of Richards et al relations (I'm particularly interested in settlements - alas, Das' book has no closed-form solution, only those hateful graphs).
And has the method been overpassed by more recent and updated studies (even though I'm not aware of other studies on settlements in seismic conditions, except something on USACE using penetrometric data).
Or maybe such methods just don't work too good in practice?

 

[Mccoy]

Mmmmmmmmm......

your silence is meaningful enough,
evidently the method ain't so popular.

May be I'm going to have a stab at it, in such case I'll let you know!

 

[BigH]

McCoy - I've got Steven Kramer's book on "Geotechnical Earthquake Engineering". Although written in 1996, it does not even mention your 1993 reference and his list is extensive - he does reference a 1979 paper by your authors. In the whole of the book, he doesn't appear to talk at all about bearing capacity but he does talk extensively about settlements and the aspects of their occurence during an earthquake. He spends a lot of text on liquefaction potential - which he obviously thinks is the most important aspect - if it liquefies, you get the settlement problems. His foundation sections seem to talk about response of structures and the IBC. I think it would be a good book for you to reference.

 

[Mccoy]

BigH,
as a matter of fact we all know how the bearing capacity topic has been overresearched, and literary redundancy is not at all correlated to its usefulness in practical field design.
After all, with the exception of cohesive saturated soils, long before reaching the failure state the structure usually settles a lot, and becomes unserviceable.
Only, local regulations request a bearing capacity analysis, and the recent shift toward reliability base design has led to the probability-of-failure concept, which you figure out figuring out bearing capacity (and loads) first.

Kramer is darn right: if the soil is liquefiable or loose enough , then problems in dynamic conditions are overwhelming.

I think on Day it's reported the common practice in the States to increase bearing capacity safety factor by one third to allow for seismic conditions, and damage to foundation-soil system has been rarely observed after earthquakes.

Observation-wise I can't say much. In my place, a seismic one, overdesign of foundations and structures is the rule and only few areas have unfavourable soil conditions. It will all be put to test when the next big earthquake comes along, I reckon...

 

[BigH]

- sorry about AC Milan! But give Liverpool credit.

 

[Mccoy]

BigH,
Mr Berlusconi,
the owner of AC Milan, one of Italy's richest men and Italian premier, has not shown to be overly sorry for the defeat. He went: "we'll have a 2nd opportunity in the cups tournament", or some like that.
Considering he's just recovering from recent unfavourable political events, he took it pretty well.
If he isn't going to be re-elected, next year, I doubt his huge project of the Messina bridge (connecting Sicily to the peninsula) will ever be started. Very interesting construction project, with serious seismic problems (the Sicilian strait is crossed by a main active fault and the bridge axis would run normal to it!). Dr Jamolkowski has already started showing slides on properties of the conglomeratic foundation soil. If interested, I'll show you the link.