Posted by Ben on July 17, 2003 at 20:51:51:
I'm building a frame garage addition with a 2nd story (bedroom) above the garage. In figuring the load on the wall, I came up with a figure of approx. 1500 lbs/ft., well below the textbook limit of 4725 lbs/ft. for a 6" wall with type N mortar. Since it's to be framed with 2x6's I elected to use a 6" CMU wall from 3' below grade up even with the top of the 6" reinforced concrete floor slab. As a thermal break is required here, the slab will be inside the wall, seperated from it by insulation, resting on the gravel fill, not resting on the top of the wall.
The slab has not yet been poured, and no building structure has yet been placed on the wall. I intended to put #3 rebar 16" o.c. down thru the wall and grout it with cement. The walls were insulated on the inside with 2" polystyrene foam.
The grade level around the outside of the building, (and also the amount of #2b gravel fill inside the building) is 6" below the top of the CMU wall along the front wall and approximately 42" below the top of the CMU wall at the back wall, the side walls tapering from 6" to 42" evenly.
This is where I got into trouble....
To make access easier, I decided to go ahead and place the gravel inside the foundation and do the rebar/grouting from inside before pouring the concrete slab. (I know, I know, I should have done the rebar/grouting from a scaffold.)
Today, one of the side walls, 26' in length (2 pilasters) suffered a spontaneous tip-over failure. As it had to be hand backfilled, we had not backfilled it yet (I know, I know, should not have put the gravel in before backfilling it).
The odd thing about it is that this was the first wall we layed (longest cured) and as it was parallel to the fall line of the grade, the amount of gravel behind it was just the space between it and side of the vertical footer trench (about 8") for a significant part of it's length.
The amount of gravel behind the back wall is much larger as it starts at about a foot wide at the footer and tapers up at about a 60 degree angle away from the wall. The gravel had been in place and holding for about 2 days when this happened, and the back will did not move when the side wall blew out.
My question is this.... am I in danger of having the same thing happen to the 29' long back wall (2 pilasters) and should I tear it down, re-excavate it and start over with larger block, remove the gravel and go ahead with the rebar/grouting, or just proceed with the rebar/grouting carefully?
Should I put off pouring the concrete floor until after I have the weight of the building on the wall?
HELP!!!!!!