Minimum slope limit for lateral spread

[Hunter64]

Hello.

What is the minimum slope limit for lateral spreading to occur? The MLR by Bartlett and Youd (1993, 2002) gives limits at 1% m while some other publications have limits are at 0.25%.

The site in my analysis has a slope of 0.01% very far from any body of water, which i'm arguing that lateral spread will not occur.

Thanks for the help.

 

[oldestguy]

Ya gotta explain more as to where you are and what is potentially spreading. It could be when a stout woman sits on a level flat seat that she doesn't take more width than when standing per your evaluation. That's "lateral spread" by one terminology.

How about that deflated foot ball owned by the Patriots?

 

[Hunter64]

I'll try to explain: urban setting with an almost flat surface. A 1 m non-liquefied sandy silt layer is assumed to slide during the liquefaction of a loose sand layer 5 m deep. I am using a PGA of 0.528g.

 

[Mccoy]

Hunter, the references I found by googling define lateral spread as occurring when the slope ranges from 0.1% to 5%. The authors cite the same Youd and Bartlett you cited. page 3 of the book

https://books.google.it/books?id=3j...e&q='lateral spreading' minimum slope&f=false

Anyway, am I missing something?

0.1% means a 1/1000 slope, that is, 0.057 degrees of slope, a quantity which is very small and maybe within the error of the surveying methods (I'm no surveyor, so I'm just guessing).

Your slope 0.01%= 0.006° of slope, a 1.75 millionth of a radian, to all practical effects is a flat surface, I don't know if such accuracy in measuring the angle of the topographic surface is granted.

It would seem that your surface is a flat one, has it a meaning to speak about lateral spreading?

http://www.mccoy.it

 

[Hunter64]

Mccoy

I was wondering if the MLR models for predicting ground displacements would cover as low as S = 0.01%. Otherwise, from my knowledge, a flat surface would fall on ground oscillation behavior

Thanks for the reference, I will look that up.

 

[IRstuff]

Neither here nor there, but 0.006º is 105 millionths of a radian, which is consistent with 1/10,000 ~ 100 microradians

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[Mccoy]

Thanks very much for the correction IR, I just verified I was reading the wrong cell with a spurious result in my spreadsheet.

By the way, after your post I'm just now noticing that, with low y/x ratios, starting from about 1/200 downward, the ratio is exactly equal to the angle in radians in the Excel 2013 spreadsheet.
i.e.: arctan (1/100) = 0.0099997
arctan (1/200) = 0.0050000 = 1/200
arctan (1/10000) = 0.000100 = 1/10000

So, Hunter64's slope 0.01% = 0.0001 = 1/10000 slope = 1/10000 radians =0.1 milliradians = 100 microradians.

This is not the spreadsheet section but I Wonder if there is anything wrong with that. I get 0.006° with a 1/9550 Y/X ratio, whereas arctan(1/10500)= 95.2 microradians

http://www.mccoy.it

 

[killswitchengage]

All i know is that lateral spreading defies mathematical computation, i think you should raise the factor of safety

 

[EireChch]

I would of the same opinion as the OP. The site is flat for all intense purposes. With the absence of sloping ground, free faces, changes in topography lateral spreading should not be an issue!!

 

[killswitchengage]

Eirechch , lateral spreading in it self happens only in flat slopes especially in shale formations , so he have to the right to be afraid
IF its completely flat i don't think there is a problem

 

[EireChch]

@ killswitchengage I don't understand your reply. You say it happens on flat slipes but if it's completely flat you don't think there's a problem. Without a free face or sloping ground there's is no where for to to spread to.

I've seen cracking on flat sites which can look like lateral spreading however this is mainly due to a drastic change in ground conditions

 

[Mccoy]

I'm reading one of the original Bartlett & Youd article (attached to this post). They cite the Shinano river plain away from the river face with lateral spread occurring on a 0.2% slope away from the river.

I'm still wondering about these measurements of an irregular topographic surface, taken with astronomical precision.

That's about a 2 milliradians angle, 2 meters of height over one kilometer of horizontal lenght, evidently it's an average over a large lenght of say, a few kilometers. So I would answer to the OP that, in this context of a wide alluvial plain or whatsoever plain, less than a 1/1000 slope angle averaged over a few kilometers sounds as a reasonably safe lower bound of the occurrance of lateral spreading.

It would also be interesting to carry out some sensitivity analysis over the formulas cited in the article. The formula (11) is logDh=0.430+0.442logS Assuming that's decimal logaritms:

Which means that slope, even if very small, has a significant effect by itself. But then we should carry out the sensitivity anlysis and scale out the effect of slope with the other variables, as in formula (20c).

www.mccoy.it

 

[killswitchengage]

In Terzaghi and al book as well as another book from Roy E hunt about lateral spreading , they cannot comply to mathematical solutions . This phenomenon defies mathematical reasoning

 

[racookpe1978]

I would of the same opinion as the OP. The site is flat for all intense purposes. With the absence of sloping ground, free faces, changes in topography lateral spreading should not be an issue!!

I'd look at the problem the other way around. The original surface (nearly) perfectly flat (assuming the slope percent numbers are valid). Therefore, any "almost liquid" substance poured onto the surface is going to keep spreading until it hits a curb, dam, or block. Or a ditch, drain, or opening. Then it will fill the opening. That is, the OP's problem is that nothing will stop a near-liquid from spreading at in every direction.