Hillside Design

[tedamiao]

This is a tough situation and I hope your experienced engineers can give me a hand.
It is 3 story house on hillside (V:H>1:3) in Los Angeles. How can Hillside design requirements section 1666 be waived? I have never done hillside house design. Can we do following (please refer to attached section)?

Build a tall retaining wall with concrete mat foundation around the entire house. Floor joist will be attached to retaining wall; the entire house will be sitting on mat foundation. My understanding is the house is on a level pad and Hillside requirements shall be waived. Is that true???

If that can not work, how about if we leave 2ft gap between house and retaining wall, hillside requirement will be definitely waived, correct?

Any advice will be highly appreciated.

 

[csd72]

Not experienced in CA but I dont think that is the issue, the issue is more likely the possibility of as general slope failure surrounding the building. I dont think any of the above solutions will resolve it.

Think of a semi circular failure surface under the house and surrounding soil. I have actually seen the results of this type of failure.

 

[tedamiao]

No, it is not soil problem. It is seismic design problem if using hillside design requirements. Most critical problems are wood shear walls can not be used, need design a lot of primary anchors and secondary anchors. Design is tough and of course, construction cost will be increased a lot, a lot....

Any body got more ideas?

 

[msquared48]

In the diagram link from your post, I saw concrete shear pin(s) - piles to be more exact - under the wall. If this diagram was created by another party, I think the scenario painted by csd is what they were thinking - to penetrate the slip circle and avoid a rotational failure due to a seismic or rain induced landslide event such as we have all seen in Southern Califormia over the past few years.

Mike McCann
McCann Engineering

 

[tedamiao]

Thanks, Mike and csd72,
The diagram was creasted by us and pile will be designed by us as well. Also,please note, we are using Mat foundation (can be 12'' to 24'' thick if needed). Retaing wall will be designed as cantilever wall.
What we are trying to do is away from hillside design requirements. Any suggestions?

 

[HouseBoy]

I am not familiar wiht the provisions but in looking on line, I think it says "on or into slopes..."

I would thihnk that means you can not wave the seismic design rewuirements.
Additionally, it seems that the retaing wall design fo rseismic requirements would be significant.
Also, I wonder how differences in bearing conditions are handled. I'm thinking that part of the structure is on deep foundations and part is on shallow. Not familiar with soil types there but generally (around where I work-Cincinnati Ohio) deep and shallow footing settlement differences can be an issue.

 

[tedamiao]

It is rock site. Main purpose of caisson is for sliding resitance rather than bearing. Seismic load is big for retaining wall but is doable for concrete wall. Main issue is how can we make house wood construction except retaining wall.