Replies

1. 
   Rob_Dykeman | Apr 03, 1999 05:13pm | #1

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   More info is needed. What is the thickness of the wall, rebar pattern, how much backfill agianst the wall, drainage being installed, type of waterproofing. These are the issues I would be concerned about on a wall the size you are speaking of. I also would be concerned of a wall of that size with no support on the inside. My curiousity would be what is this wall for?

2. 
   Guest_ | Apr 03, 1999 05:36pm | #2

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   Morning Brian,

   I do believe as Rob has indicated that, first of all you would have to give us a lot more information.

   More importantly, you must realize the seriousness of your request. This is a structural wall that is outside the parameters of any residential advice or comments.

   You MUST take your plans to an engineer for approval. We don't know if your in an earthquake zone, we don't know the kind of rock your founding on, we don't even know the intent of the building.

   Again, you MUST take you plans to an engineer.

1. 
   Guest_ | Apr 06, 1999 04:06am | #4

   *First as Rob and Gabe indicated "need more info"However I run into bedrock on every job I do here on the southern Gulf Islands of B.C. And believe me the soundness of bedrock can vary greatly from site to site even within 20' on one site. What you need is a "geotechnical engineer" These engineers specialize in soils and rock mechanics and the stability of these. In sound rock we generally grout 5/8" rebar in 1 1/2" by 2' deep holes on 3' centers using a cement based expandable grout. We get the blasters to drill the holes because these guys have the equipment to do the job quickly and efficiently. On some jobs where the rock is very fractured and weak the engineer has required holes up to 8' deep, yes eight feet. Sometimes the rebar size is also upgraded to 3/4" or even 1" on rare occations depending on various structural cicumstances.When placing concrete walls on bedrock footings are rarely required. The reason we use footings is to spread the load of a structure out over a larger area to increase stability. Most residential buildings rarely require soil bearing capacities greater than 2000 lbs per square foot. All but the weakest of rock greatly excede this load bearing capacity. Therefore you most likely can place the wall direcly on the rock. If the wall is to be block or brick the footing will be needed only to provide a level surface to start the first coarse of block.I am assuming that by the way your question was worded the wall will not be back filled on the exterior of the wall. You also mentioned a cold climate so I am assuming you are concerned about frost getting under the footing and creating havoc with your wall. I run into this situation frequently here as well although it rarely stays below freezing for extended periods of time. As long as it stays dry under and around the footing you shouldn't have a problem. If this is a potential problem you could run heating cables in the footing to prevent freezing in the winter.If the wall is going to be backfilled you have bigger things to worry about. All that backfill will create tremendous lateral pressure. You will definitetly want to go with concrete walls, The rebar dowels into the rock will have to be bigger to prevent the wall from shearing off of the rock. You will definitely need buttress walls on the inside of the building. This is where you will definitely need an engineer.

3. 
   Brian_Lumley | Apr 06, 1999 04:06am | #3

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   I am preparing to lay a foundation for a building on exposed bedrock in a cold climate. The building will have 20 ft. high masonary walls approximatly 55 ft. long with no inside walls for lateral support. I am going to use anchor pins tied to horizontal rebar. Any ideas on how far apart the anchor pins should be and how wide and deep the footings need to be?