Footing and Foundations on surface Bedrock
Footing and Foundations on surface Bedrock
(OP)
Good Day to all!
We are designing a home on a site which is 95% surface Bedrock. The Topo conditions vary from moderate to severe slope conditions. The Code Frost depth is 3'-6". My question may be silly but, does the surface bedrock need to be excavated (by blasting or hammering) down to the 3'-6" depth in oder to avoid any possible damage due to freezing/thawing? If so, is there a documented reference book I could purchase for insight? If not, what depths and or method would be proper?
Most likely I am mistaken, but for some reason I keep thinking that a footing or foundation wall, which has been pinned properly to bedrock but ABOVE the 3'-6" frost depth, may have water infiltration between the rock and concrete over time. If so, would'nt this cause problems?
Your help is greatly appreciated and respected! Thank-you!
We are designing a home on a site which is 95% surface Bedrock. The Topo conditions vary from moderate to severe slope conditions. The Code Frost depth is 3'-6". My question may be silly but, does the surface bedrock need to be excavated (by blasting or hammering) down to the 3'-6" depth in oder to avoid any possible damage due to freezing/thawing? If so, is there a documented reference book I could purchase for insight? If not, what depths and or method would be proper?
Most likely I am mistaken, but for some reason I keep thinking that a footing or foundation wall, which has been pinned properly to bedrock but ABOVE the 3'-6" frost depth, may have water infiltration between the rock and concrete over time. If so, would'nt this cause problems?
Your help is greatly appreciated and respected! Thank-you!





RE: Footing and Foundations on surface Bedrock
Rock can be tricky to engineer, depending on the loads. Suggest you contact a local geotechnical engineer who will be more eperienced with local code requirements and past building experience in the area for similar strucures.
Jeff
RE: Footing and Foundations on surface Bedrock
Site grading to direct water away from the footings should also be incorporated into the design.
Good luck with your new house.
RE: Footing and Foundations on surface Bedrock
RE: Footing and Foundations on surface Bedrock
Thank-you very much for your suggestions and guidance. We are looking to bring in a Geotechnical Engineer. We have isolated the rock structure as Proterozic Rock with no sedimentary covering. More specifically, Horne Blend Granitic Gneiss.
Thank-you again!
RE: Footing and Foundations on surface Bedrock
Good luck.
RE: Footing and Foundations on surface Bedrock
Generally the Geotech or structural engineer has to have a P.E. and sometime4s it takes a meeting with the inspector's boss.
Another one is where does that magic depth of frost figure come from?
RE: Footing and Foundations on surface Bedrock
RE: Footing and Foundations on surface Bedrock
RE: Footing and Foundations on surface Bedrock
We are currently building a long (60m) double story building, with two expansion joints at aproximately 20m.
the foundations are reinforced concrete strip foundations in fairly good weathered granite gravel soils.
The problem i have is that the last 10m of one of the strip footings will end up on exposed solid granite rock. the site is quite steep with the rock section sloping at about 30deg.
I am worried that i will end up with cracks at the transition from insitu material to rock if i continue with the strip footing onto the rock (it will be pinned into the rock by drilling and grouting in reinforcing bars)either from differential settlement or from differential expansion contraction of the rock as in winter here we have quite warm days (15-20 deg C) and cold nights (down to about -3 deg C).
should i add another expansion joint at the transition? any suggestions will be appreciated
RE: Footing and Foundations on surface Bedrock
Analyze the thing and you will know where you are.
RE: Footing and Foundations on surface Bedrock
RE: Footing and Foundations on surface Bedrock
Overexcavating the rock would require blasting, and it is not an option. think we will go with the isolation joints
RE: Footing and Foundations on surface Bedrock
You've got pretty massive bedrock that wouldn't soak much water, nor bump around too much from frost, I shouldn't think.
Still, It would be prudent to drain the grade away from the foundations with impermeable soil, or synthetic and maybe add foam insulation, but thats your call since you need to consider some heat movement from inside....
It would be advisable to add some rebar in the footings to provide a transition between the rock and overburden.
RE: Footing and Foundations on surface Bedrock