Need help with foundation design on Bedrock
Need help with foundation design on Bedrock
(OP)
I am building in Northwestern Ontario (Canadian Shield) on bedrock. I had the site scrapped down to rock when i had my road built and will shoot some elevations this weekend.
The area is fairly flat with only a few impressions, i would estimate the elevation difference, highest point to lowest point be approx 2ft. I will know for sure by Monday.
I am building a one level home, with in slab heating. I was planning on a thickened edge slab as shown in the attachment. I am not interested in a crawlspace, as I see the problems they create everyday ay work (I know if they are built correctly they can be problem free, but want to avoid it).
I had a builder I know looking at my site and he was concerned that bringing in fill for a thickened edge slab is a bad idea, as the hydrostatic pressure would cause it to move down hill (it slopes slightly towards the water and a very high cliff for that matter)and will not get a good compaction.
I am sure many of you are firm believers of building on bedrock, as all contractors/engineers in this area are.
I am looking for inputs on how to scribe my footings to bedrock, while having a "slab on grade" type home. I will attach another sketch, showing a 10inch footing, scribed to bedrock, 8 inch min height, with a 6 inch slab on top I am thinking of. My concern with this is the rebar left exposed that will go into the slab will be in the way of the compactor. A guy i work with assumed they can just bend the bar down after compacting the fill and laying the ridged insulation, but his background is in mining.
I am fairly new to foundation design and all the input is appreciated.
The area is fairly flat with only a few impressions, i would estimate the elevation difference, highest point to lowest point be approx 2ft. I will know for sure by Monday.
I am building a one level home, with in slab heating. I was planning on a thickened edge slab as shown in the attachment. I am not interested in a crawlspace, as I see the problems they create everyday ay work (I know if they are built correctly they can be problem free, but want to avoid it).
I had a builder I know looking at my site and he was concerned that bringing in fill for a thickened edge slab is a bad idea, as the hydrostatic pressure would cause it to move down hill (it slopes slightly towards the water and a very high cliff for that matter)and will not get a good compaction.
I am sure many of you are firm believers of building on bedrock, as all contractors/engineers in this area are.
I am looking for inputs on how to scribe my footings to bedrock, while having a "slab on grade" type home. I will attach another sketch, showing a 10inch footing, scribed to bedrock, 8 inch min height, with a 6 inch slab on top I am thinking of. My concern with this is the rebar left exposed that will go into the slab will be in the way of the compactor. A guy i work with assumed they can just bend the bar down after compacting the fill and laying the ridged insulation, but his background is in mining.
I am fairly new to foundation design and all the input is appreciated.





RE: Need help with foundation design on Bedrock
RE: Need help with foundation design on Bedrock
Don't ask about what to do with the sewage....
RE: Need help with foundation design on Bedrock
Also, I recommend the rebar dowels if sliding is indeed an issue. But I wonder how much of an issue it is. You described a flat site and not much of a reason to worry about it. If the pad is graded flat prior to placing the foundation then how does the slope around the pad effect it from sliding?
Jim Houlette PE
Web: www.evstudio.us
Online Magazine: www.evstudio.info
RE: Need help with foundation design on Bedrock
RE: Need help with foundation design on Bedrock
If you have resources and specialists, why risk not using them? Sorry if I am ranting.
RE: Need help with foundation design on Bedrock
Also the only design firm in town (closest city is Winnipeg, 2.5 hrs west) does not have a geotech guy on staff. I work with 2 former employees of the firm and have been picking their brains on the subject. As far as liability goes, it will be an owner design/build and the permitting in the area does not require stamped drawings, I do not think their will be any issues there.
As far as the site goes, there is no question at all it is solid bedrock. I am looking for the most practical way to build a proper foundation while maintaining the in slab heating and avoiding crawlspaces.
RE: Need help with foundation design on Bedrock
Just wanted to add another point - should you go for the grouted dowel into the rock (which we use often in foundations on the mountainside in Cape Town), go for a slightly thicker bar so that allowance is made for dowel corrosion over the long term. This is minimal in terms of cost but gives one peace of mind for the long term. I assume that a seasonal perched groundwater exists at your site which would affect the grouted dowel bar.
Cheers and good luck.
RE: Need help with foundation design on Bedrock
Good tip, I will definitely keep that in mind when I decide on a design.
Thanks,