Expansive soil and retaining wall 1

[DoubleStud]

I have a residential project where I will have to use drilled piers because of the expansive soil. For the deck, I will make sure that each post will sit on a drilled pier. How about the stringer support for the stairs to the deck, do you think it is necessary to have drilled piers to support the bend of the stairs (wood framed) and the very bottom of the stringers? Or perhaps we can have stringer connections that are able to rotate? Or shall I go ahead and add 4 more drilled piers?

This project also has a retaining wall that is not connected to the house. Do you think it is OK to just do a typical cantilevered retaining wall without using any drilled pier? We are trying to minimize the # of drilled piers. I am thinking if the soil does expand, the whole retaining wall will move with it.

 

[Aesur]

If it were a steel stair I wouldn't hesitate to just have 1 and 2 and cantilever to 3 and 4, but being wood, I believe you should have 4 drilled piers there due to the bend in the stringers.

I assume being that you know it's expansive soils that there is a geotech involved? If so, I suggest asking them. Maybe consider putting more control joints in the retaining wall to mitigate damage. I haven't had a project to date that I haven't been able to do a continuous footing for retaining walls, but that may just be based on project locations.

 

[Tomfh]

If the stair flight can move freely against the side of house I’d be happy for the 1,2,3,4 zone to sit on higher level footing(s). The stair flight can hinge about the deck and absorb any incidental expansion or contraction of the soil.

If however the stairs are going to bind against the house then I’d want all of it on deeper footings.

 

[DoubleStud]

Aesur, I will talk to the client and architect about the deck.

For the retaining wall, that is a good idea. So are you saying to stop and start the reinforcement and put a joint every 10-15 ft? Put a filter fabric perhaps at this joint on the soil side? Would you be worried that the each wall segment will deflect differently? I am worried maybe one area is wetter than the other. Do I need something better than just a butt up joint?

 

[JoelTXCive]

At the bottom of the stairs, could you reduce the 4 proposed piers to just 2 piers located at the Centerline of the stairs. Then pour a pier cap that will catch all your columns?