Regular or structural slab 1

[afk2000]

Hi,

I am trying to build a new two story house on a slopped property, the soil report shows that I need to have piles & grade beams, the whole floor of the building is going to be a flat slab on grade (because I have a retaining wall behind the building).
Now here is my question: Does this slab need to be a structural one-way (or two-way) slab, or it can be a regular slab on grade?

Thanks in advance for your future comments.

 

[SlideRuleEra]

When pile supported, use a structural slab and design it as if the soil was not even there (other than as a convenient, temporary bottom form for the concrete). Trying to share the load between piles and soil is a recipe for trouble.

http://www.SlideRuleEra.net

 

[afk2000]

Thanks for reply.

 

[ironmon]

Well, i know that on the New Jersey it is common to have the house framing on piles and the 1st floor slab/garage slab on grade.
It will depend on the use of the slab, the specific soil conditions and how much movement you can tollorate.
I would ask the geotech for his opinion.
It is certainly conservative to support the slab on the piles.
I would think for a residential application, the slab on grade is generally the more widely used approach.

 

[gotwood]

I wouldnt put slab on grade on expasive soil if it was my design. Here in colorado, a lot of people put slab on grade on their expansive soil to save cost (shorter foundation walls, easier to build), and they end up having cracked slab and unlevel slab. Here is the theory, if you for some reason design the slab as 2 way slab sitting on grade beams, I would think you want spacing between the slab and the grade. If you dont do this, I think it will defeat the whole purpose of drilled piers because the soil will easily lift your whole structure when its wet because it has more bearing area. If you put crawlspace underneath than the only uplift area would be the area of the piers that will be counteract by the dead load and the skin friction of the piles.

 

[gotwood]

Oh also, if you do decide to use slab on grade, I would put control joints and do not tie the slab into the foundation. Maybe put 1/2" Exp. where it meets the foundation/grade beam so that the slab will not lift the whole house.

 

[gotwood]

Oh, after reading your post again, the reason they suggest drilled piers was not because of expansive soil i guess. I guess its because of the slope. So disregard my posts.

 

[AsianEngineer]

I have the same situation in a Residence I'm working on now. In the soils report that I received it mentions that the slab on grade may be design as a "floating slab' or structural slab. So, I would definetly talk to your Geotech and get his/her recommendation.