20' high basement wall and diaphragm

[bylar]

Basement walls of 20’ in height
Residential
IBC 2006 North Carolina

Paragraph 1610.1 “Basement walls and other wall in which horizontal movement is restricted at the top shall be designed for at rest pressure”

Exception basement nor more than 8’ below grade with flexible floor

Similar wording in previous code

Table 1601.1 for most sandy types of backfill has an at rest pressure of 60 psf

For reinforced masonry with 12” CMU that puts a limit at about 12’ with 11’ of backfill.

If you go to concrete then the wall is possible but the resultant at the top is app 2100#/ft.

With a typical ¾” plywood floor as a diaphragm the plywood is overloaded.
Any ideas on how you have solved such a situation

 

[miecz]

concretemasonry-

Diaphragm action? Do you dowel the slab to the side walls? Do you provide a reinforced slab with no control joints?

 

[ChipB]

bylar,
What I have done in the past (Cashiers, Brevard, Asheville) is design a segmental retaining wall outside of the foundation wall. I place 4' between the two, and provide a walkway to the residence. This makes it into a tall foundation wall. The bottom of the segmental wall is near the bottom of your bldg footing, however, you do have to take the resultant force of your segmental wall, and place it on whatever backfill you still have against your foundation wall. Usually is not too big a deal. Just be careful with your slope stability. Use Mesa Wall for your analysis as it will do a global check for you. Call out for verification with a geotechnical engineer in your general notes.

I, personally, think it is a brilliant idea. However, I can't take credit for it as I initially saw it done at a house in Hendersonville, before I decided to incorporate it. I don't know who the engineer was for that house, however, I owe him (her) a big thanks!
Chip

 

[bylar]

icenine Most of the area is solid rock and I dowel with epoxy set into the rock along with chiseling into the rock for the footing.
We do have a basement flooor of concret and it offers some friction resistance and I design it as deep beam and dowel into the side walls. Again I have to dowel the side walls into the rock. Those items all work but my original question was using the code requirements of 60 psf earth load is there anyway that plywood diaphragms from the floor will work. My answer is no and that it has to be a concrete floor but I respect the ideas of those active on this site.

 

[IceNine]

Bylar-

The sliding resistance you've provided makes sense. As for the plywood floor, I agree that there's no way to make it work...Unless you design the wall as cantilevered (with counterforts?) and backfill first, or build a segmental wall in front (if possible) as Chip suggested. I guess it comes down to the cost of building the large retaining wall vs. the cost of two concrete floors and the beefed up framing required to support these floors.