Newmark method for seismic slope stability

[Mccoy]

hi all,
anyone of you ever tried to use the Newmark method for slope stability in seismic areas?

One major concern over here in Italy is that the new LRFD regulations enforce it, but very little is known about the allowable displacements.

Some guys are rightly pointing out that in some landslides structures remained undamaged with displacements of meters.

In my opinion much is also a function of where the potential sliding surface starts from.

Do you have any ideas at all on allowable displacements for structures (mainly residential) located on sliding blocks? (meaning treshold displacement of the sliding block before structures are damaged).

 

[Mccoy]

I managed to find some indications about displacements: authors agree that a slope is potentially unstable under seismic conditions if displacement calculated by the Newmark method reaches a treshold of 2-4 inches.
Treshold is indicated as 40 inches by an author for earth dams.
Others prefer to give indicative ranges, such as a fraction of an inch, few inches, few feet, as orders of magnitude.
The more plastic and ductile the slope material the more the allowable displacement.

Nothing is said about residential structures, but evidently they follow the slope's fate.

 

[jdonville]

Mccoy,

The only information I have regarding the Newmark method is a copy of the 1965 Rankine Lecture. No inidcations are given for permissible deformations that I can find.

I vaguely recall performing some very crude Newmark method calcs years ago. However, most of my reference material on the topic of permanent deformations due to seismic events deals with the simplified Makdisi-Seed method.

Jeff

 

[BigH]

McCoy - do you have Kramer's book? There is 4 pages on the Newmark method. I know of it but haven't used it really. I'll do some searching, though. It seems that although Italy is adopting the LRFD methods, they really aren't ready for them. In fact, it is doubtful that many are as it is more likely than not this change is due to academics and structural types - and not practicing geotechnicals.
(just listing to a little Shelly Manne and his band Live - nice !)

 

[Mccoy]

Jeff,
it's surprising how sometimes an oldish method is dug up and becomes the "hot stuff".
Actually, a main problem of Newmark's is the acquisition of a site accelerogram. More often than not, you have to fall back to the synthetic ones.

Maksidi & Seed and the other statistical method of Frankline & Cheng (sorry for the mispelling) get around that.

Howard,
true enough the structurals wanted this change, but it is stemming from the Eurocodes revisitation of civil engineering.
Interestingly enough, I'm realizing many structural engineers are suspicious of the new regulations and are trying to postpone their usage as long as possible. Geotechs are just stunned speechless, hoping that a new law will come up, ban LRFD and relive the old methods!!!!.

 

[Mccoy]

Ah, sorry Howard,

Shelly Manne's big band is a classic, the very first jazz concert I saw, when I was 12.
Still remember his solo with brushes!

 

[BigH]

Damn - lucky boy you are. I saw Coryell and later Corea and Light as a Feather. Miles Davis in Toronto, too. Toronto Jazz Festivals.

 

[Mccoy]

This summer Mulgrew Miller is going to come over here, absolutely look forward to it. a few more big names as well, but Mulgrew is totally awesome, refined and modern and traditionalist at the same time.

Here in italy Newmark is arising more and more interest, I read the Kramer stuff provided by Howard, there are some interesting simplifications suggested, cited in other books as well (i.e. Robert Day's "geotechnical earthquake engineering").

Equations where you just need the Peak ground Acceleration and critical yield acceleration , for some of them also Arias intenstity, and have the total displacement as an output. There are some convenient plots, with displacement percentiles as well.

Those simplified methods are going to be great until there will be an extensive accelerograms database, some areas already have it.