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Piles in slope w/ landslide
2

Piles in slope w/ landslide

Piles in slope w/ landslide

(OP)
so we're supporting a 250 ft pipe bridge on piles installed on a sloped terrain where there's landsliding but no liquefaction. I would like to know what are the checks I should do for a sound stable structure and the major factor that come into play in designing the piles, especially from a landslide standpoint.

Thank you.

Tiffany.

RE: Piles in slope w/ landslide

What does your geotechnical engineer have to say about your proposed piles in the landslide?

If the piles stop within the landslide, then they will just move along with the soil. If the piles penetrate below the depth(s) of sliding, then the piles will pick up a significant amount of lateral load. Whether they will move along with the slide and how much load they will pick up depends on many many factors. You will need to work closely with your project geotechnical engineer to determine how to address the landslide, the piles, and the load on the piles.

Best of luck, these types of situations are always very complicated and the required analysis is difficult.

Mike Lambert

RE: Piles in slope w/ landslide

As with many posts here this one is very open as to where it will go. In ordr to know more about the situation, you need to be much more complete. For instance, where is this as to country, weather generally there, topography, known geology, local jurisdictions, kind of material for pipe and contents, environmental regulations, alternative locations, etc. And, as GeoPafeTraffic says,any expert info you have. That is your first step anyhow.

RE: Piles in slope w/ landslide

Lots of factors can come into play designing piles. I’d assume lateral loads resulting from the upper sliding soils could be an issue. Your geotech should be able to provide lateral capacities of the piles in their report. Scour should be taken into account too.

RE: Piles in slope w/ landslide

You should apply 'z-shifts' and 'y-shifts' to your soil springs in your pile beam-column model and then check that this additional thrust (load) can be withstood by the piles. The specific values of the z-shift (axial landslide movement) and y-shift (lateral landslide movement) for each soil spring at each depth will come from the slope stability/movement assessment. The z- and y-shifts are essentially applied by shifting your soil springs along by that specified distance such that there is load at zero displacement.

RE: Piles in slope w/ landslide

2
I would trust you've looked at every possible means of realigning the pipe before opting to bridge the landslides.

As GeoPave remarks, piles in these situations can be subjected to enormous lateral loads, requiring specialist design by an experienced geotechnical engineer. This must be preceded by a detailed site investigation with soil borings.

I was once involved in a project requiring the design of a piled wall to support a documented landslide. Visually the landslide wasn't too major; I figured the driving forces wouldn't be that great and so opted for a low-spec investigation. Heavily reinforced piles were socketed into sound rock and tied together with an enormous capping beam, through which tensioned ground anchors were installed to the bowels of the earth...it seemed like a complete over-design to me at that time, until the ground anchors began snapping within a month of the structure being completed. One by one I watched them go until none remained...then the wall began rotating, and kept rotating. The driving force in that case surpassed anything I could ever have predicted. We drilled the hell of the site, had the design reviewed, and still everybody involved was baffled.

The driving mechanism of your landslips and the depths of the slip planes need to be very carefully established before you even look at designing piles.

All the best; and don't do what I did...
Mike

RE: Piles in slope w/ landslide

Imagine a pile in the ground.

Imagine the soil in the upper half of the pile trying to slide.

Think of how the pile will respond. . .

If the pile doesn't move, it'd have to support the soil that wants to, "Flow" around the pile. If the piles have any reasonable spacing, each pile will mobilize soil arching. That means for the pile to remain motionless, it'd have to support the full brunt of passive earth pressure times the arching multiplier. There are several folks that have looked into this multiplier, but Brinch-Hanson (sp) provides a value that's just about phi/10. So, if you have landsliding soil with a friction angle of 30 degrees and a pile with a 12-in width, you'd have a horizontal earth pressure of Kp*3.

Considering a unit density of 125 pcf you'd then have a equal vent fluid density of 1,125 pcf.

Have fun with those calculations - we haven't even started talking about p-y relations!

f-d

ípapß gordo ainÆt no madre flaca!

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