Need for dynamic soil/rock testing?

[Patgeotech]

Following all the seismic activity the world has experienced so far this year, I wanted to put the following questions out there to see what the different opinions are. If no seismic or dynamic soil properties are available, would you still design foundations/structures based on static test results (and perhaps guidelines) or would you ask for further dynamic soil testing (bearing in mind the high costs associated with some of these dynamic tests)? Assuming you work in a low seismic activity area?

We work in an area that is regarded as a low seismic area, yet the majority of engineers do not consider seismic or even vibratory aspects/properties in their designs - I find this a bit of a concern and difficult (as a geotech) to convince engineers/clients that have built many structures (without dynamic consideration)into now doing dynamic soil tests. How do you talk or convince a engineer/client into expensive dynamic testing when it has never been undertaken in previous projects?

 

[msucog]

are you in U.S.?

 

[dgillette]

There is no one-size-fits-all answer to your question. It all depends on what materials are involved, what level of earthquake is reasonably likely, where the water table is, what kind of testing can be done at reasonable cost, etc. Good SPTs or CPTs might be all you need, or you might need to spend a boatload of money on lab cyclic testing. It just depends.

 

[Mccoy]

It depends on how you define a low seismicity area and the project involved.

In Italy, even in high seismicity areas, dynamic soil testing is rarely carried out because of its cost. More often, dynamic properties are estimated. I know few exceptions to this rule.

Whereas, if you mean geophisical testing, that's the rule now.

If the area is really classified as low-seismicity though, many engineers will stick to the old, static analyses.

Of course seismicity may be re-evaluated, as has happened recently in the field of nuclear power plants...

 

[Mccoy]

This is an interesting case of a seismic hazard re-evaluation

http://www.publicintegrity.org/articles/entry/3039/

 

[msucog]

the "reevaluation" is a political agenda to look like they're doing something. the plants are designed with a very high level of confidence by the world's best/brightest based on what we currently know. additionally, the graphic posted is impressive but it is not appropriate related to safety-related structures. that is the usgs map for a 2%/50 yr probability of return (ie. 2,500 yr return period)...that's IBC requirements. i also think that picture is not even the current usgs map. nuclear facilities are designed for 10,000 yr and 100,000 yr events. reevalautions will occur and new technologies will be implimented over the coming years but that is not a sign that the nuclear industry has been cutting corners. the seismic and nuclear industry continue to revise the methodology to incorporate new hazards and to revise parameters of existing hazards as more and more information is known. i think the world should step back from the media frenzy and anti-nuclear groups and look at the technical aspects. i suggest the following workshop website

http://www.nrc.gov/public-involve/conference-symposia/seismic-info-workshop.html

for real information.

also, the publicintegrity website seems to me to be a left leaning site...i'd suggest researching who funds that group to dig further in to their motives. perhaps it would be beneficial if they would look in to the commercial industry and ask why every single state in the nation does not fully implement and enforce the International Building Code requirements. that is a much, MUCH high risk to public safety.

 

[Mccoy]

MSUcog,
the media frenzy is maybe partly justified by the failure of the Japanese to foresee a large tsunami in one of the most tsunamigenic parts of the world.

If what is reported is true, their reliability analysis grossly underestimated the water level consequent to the tsunami wave so that the emergency generators got submerged and failed.

I don't say all American sites share the same risk level of the Japanese site, anyway such a weakness in the legendary Japanese efficiency makes me worry a lot.

America is a little better off since she has vast almost unhinabited lands. I'd be pretty much worried about the sites in California though, that doesn't need any seismic re-evaluation I think you'll agree upon that.