Settlement calculation for strip footing 1

[Geosubhtech]

i have a retaining wall of 1230 m. i want to calculate the settlement for this.
i assumed as a strip footing but i am facing problems with fixing the factors in immediate settlement. Any thing regarding reference and methodology will be very helpful.

thank you

 

[EireChch]

What method are you using to calculate settlement? What factors are you talking about? What’s the soil profile?

On a side note, is this a fill or cut retaining wall. If I’m cut then you wont have any.l settlement as there’s is no net increase in load. That won’t be true if you are applying a load on the retainer side.

If it’s a filled again you will probably have minimal settlement due to the ~20kpa net increase in load. Again unless your adding a load.

 

[Geosubhtech]

Sir, i am using elastic theory formula for immediate settlement calculation. In that influence factor is there. For strip footing i am not able to find any source for that. The basic drawing for retaining wall i attached.

Thank you for your reply.

 

[oldestguy]

It would appear to me that immediate settlement is not something to be concerned with since any uneven support for the rails can be adjusted by working with the fill within the "box" as the load is added there. Instead long term settlement due to soil consolidation would be my concern. In that case distribution of stresses can be calculated for this situation by manual methods if necessary.

 

[Geosubhtech]

But for live load immediate settlement will occur. Like train loading while crossing over.

 

[oldestguy]

Then, the obvious. Routine maintenance on railroads, such as cleaning the ballast will bring things back to normal.

 

[fattdad]

[ul]
[li]figure out your loads.[/li]
[li]Determine your soil properties with depth (i.e., unit weight, soil modulus, OCR, Cc, Cv, e)[/li]
[li]Apply them - it's like flipping the switch that's marked, "Gravity."[/li]
[li]Use elastic theory to determine the attenuation of loads with depth.[/li]
[li]Evaluate whether you are exceeding the stresses of preconsolidation - let's say you are not.[/li]
[li]Make a plot of layers, stresses and moduli with depth.[/li]
[li]Integrate the change in stress with respect to depth for each layer. Divide that area by the layer's modulus value.[/li]
[li]Get settlement out of that layer. That's immediate settlement![/li]
[li]Consider that an additional 30 to 50 percent of that value could develop in time - like over the next 20 or 50 years.[/li]
[li]Let the immediate settlement occur during construction and let the over-time settlement gauge what may happen during service life.[/li]
[/ul]

So, if you have a 10 ft layer that experiences a typical stress increase of 1,000 psf and has a modulus value of 200 tsf, that'd return 0.3 in of immediate settlement. And (likely) a trivial 0.1 in of settlement in the decades beyond.

f-d



ípapß gordo ainÆt no madre flaca!

 

[Geosubhtech]

Yes i am using Elastic theory. but i am facing issues with the influence factors ( like bowels used in book). For strip footing no charts are available.

 

[fattdad]

You don't need influence factors!

It's as simple as PL/AE! You got the P (it attenuates with depth), you got the L (the layer thickness), you got the A (just use one unit foot for simplicity) and each layer has it's own E. Calculate away!

The point I'm making is that all your calculated settlement will occur as the earthwork is completed, but. . . There's a separate term to gauge the long term strains after the effective stresses have normalized. It's sort of a C-sub-alpha term for granular soils.

According to my, "Settlement Manual" (Duncan and Buchignani, 1976) the time rate correction factor for 3 years is 1.3, the time rate correction factor for 10 years is 1.4 and the time rate for 30 years is 1.5. So if you calculate 4 inches of immediate settlement and your design life is 30 years, you'd expect an additional 2 inches of settlement during the service life.

Good luck.

f-d

ípapß gordo ainÆt no madre flaca!

 

[Geosubhtech]

Thanks for the reference and reply.

 

[L0k]

Immediate settlement formula is based on the elastic condition and one of them was given by Schmertmann. This may be an option to consider.

 

[BigH]

For any elastic theory - check out Poulos and Davis' "Elastic Solutions for Soil and Rock Mechanics" - google it and it can be downloaded

 

[Okiryu]

shub, the last week I was also looking at the Bowles influence factors (I guess you are looking for the depth influence factors). Anyway, here is a link to download Bowles programs that are referred in his book. I guess you need to look at the FFACTOR program. You need C++ to run these programs...

http://www4.hcmut.edu.vn/~cnan/BOWLE/Foundation Analysis and Design CDROM. Bowles/EXE/

 

[Geosubhtech]

Thank you okriyu. I already finished that calculation by using bowels programs. Anyhow i am getting settlement of less than 3 mm for live load (immediate).