Helical pile foundation on steep hillside

[sebas-1024]

Hello,

I'm looking to evaluate the feasibility of using helical or screw piles for the foundation of houses on a pretty steep hillside (about 30º). My initial assumption is that it's definitely possible, I've seen some constructions that have been done in that manner but they seem to be pretty simple, what I mean is that they have no parking lot, only one story, or they aren't really large, and all of these are things that are present in the project that I'm evaluating the foundation system for. But of course, what I'm looking for here is any input from someone who's had experience in the design and/or construction of these type of foundations in the conditions that I mentioned. I'd like to hear if the system is more expensive, what should I look out for in that type of terrain, or maybe if a combination of foundation systems is required?

Any input that you can give is more than welcome, and thanks in advance.

 

[r13]

In the 70's, we had a project on top of a hill, that was about 150' above a city correctional center. One night, the near complete structure slide downhill, and became back yard neighbor of the correctional center. Reason for the unfortunate event - slop instability on land over fill. This story serves as a note to remind you the importance of soil investigation before foundation system selection.

 

[theCorkster]

Dittos to r13.

Also, while it may be feasible to install the piles, when they come near the colluvium/bedrock interface they will likely deflect and not embed into bedrock (which you have no way of knowing what is going on). Finally, there will be some long-term component of down slope soil creep that will add lateral force to the pile. So what do you believe you'll really end up with if you do not know the geologic/soil conditions you propose to build on?

 

[Mad Mike]

Ditto to both of the above.

Are you not preparing a bulk earthworks platform prior to piling the foundations? Or are you suspending structures over the 30 degree slope, which I'm assuming is a natural slope as opposed to a fill embankment?

Your post suggests it's quite a large development, so I'd be more concerned about the retaining structures around the platform on such a steep natural slope, than the foundation installation from finished platform level.

You haven't mentioned the ground conditions at all, and the feasibility of what you're proposing is largely governed by them...

Best,
Mike

 

[oldestguy]

Time now to get a local geotech engineer involved. Can be a complicated mess to work this out.