Foundations of a large building on a slope

[Sjotroll]

Hello! I'm currently working on this project where a large building is being constructed on a slope. The static calculations have all been done and our job is to design the construction pit. We noticed on the drawings when looking at a cross section down the slope that all the "parts" of the building are presumably founded on strip footings, but all on the same absolute depth even though it is a cascade building with bottom floors on different depths, meaning that some walls on the upper part of the hill would extend over 10 m into the ground just to be founded on this strip footing held on the same depth as all others. Obviously we found that very strange and are almost certain this doesn't have to be done that way, it just looks wrong and there are much better solutions for the problem if there really was a reason for them to be on the same depth. We do have in our national standards recommendations that all footing should be on the same depth, of if not then the maximum slope between neighboring footings to be 1:1 with maximum step of 50 cm. There are reasons I can think of to justify these recommendations, but on the other hand, if we need a wall long 10 m going into the ground just to end on a strip footing, for which we need enormous quantities of excavations to construct, then isn't it better to change the foundation system to piles in those cases? But surely not all cascade building constructed across the slope are founded on piles in the top area, right? Obviously there is the problem of slope stability, but as I said in my opinion there are better solutions for that. I'd like to hear your expert opinions and experiences on this subject.

 

[EireChch]

Sounds like complete madness.

Show us a cross section of the slope, including a description of the ground conditions.

Shallow foundations on a slope can work provided you confirm the slope is stable.

I have never seen a requirement to have foundation all on the same level. This shouldn't apply to hill sites. Pilling of hill sites is common though. In some instances you might support the portion of the building closest to the slope on piles and the back portion on shallow foundations. Tapering the pile length beneath the building to meet shallow foundations reduces the potential for differential.

 

[Sjotroll]

Here is a simplified but representative cross section of one part of the building, with sketched layers. As you can see, the footings are placed all on the same depth, and far below the floor level in some cases. The most concerning part is the footing on the rightmost side because it would mean that a very deep embedded wall is needed there just to construct that one strip footing and then cover it again.

I have never seen a requirement to have foundation all on the same level. This shouldn't apply to hill sites.

This certainly makes sense, unfortunately the code doesn't say anything specific other than that generally the footing shall be constructed the way I mentioned in the post.

 

[dik]

Could you do something like this, where the SDF is a stepped down footing detail... the footing on the right side may have to be lowered to maintain the 1:1.5 slope.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[HTURKAK]

Sjotroll (Geotechnical);

The section does not give necessary info. regarding the architectural spaces required.
My initial approach will be similar to the following, the yellow portions are blinding concrete fill.

If you write STEPPED FOUNDATION and search the web or look to foundation engineering bokk you will get some idea which will conform to your specific conditions.