I used 8" 3-core block for the foundation on top of a 8" deep x 20" footing. I reinforced the footing with 2 courses of 1/2" rebar.
The block wall is 12 blocks high (approximately 8' in height). The top course of block is filled with portland Cement.
We then built the frame of the house (2x6 construction) and installed the roof trusses. We also installed the 1/2" plywood to the all of first floor walls.
At this time, we decided there was enough weight on the foundation to resist any lateral forces that backfilling could produce. The front and sides of the house were only backfilled to about 6 block (48") high. However the back of the house was backfilled to 10 block (80") high due to the grade of the lot. Before we backfilled, we added about 1-2 feet of gravel for drainage over the french drains.
A few weeks ago, we borrowed a skidloader and backfilled. We then sheathed the upstairs walls, and also sheathed the roof. Yesterday we loaded the shingles up the roof and today we were working on soffit and fascia. I needed a pair of snips and they were in the basment. When I went down to the basement, I noticed that the back wall(which was backfilled to 80", had a horizontal crack running almost completely along the 44' of block wall. The seam was about 64" high. The wall apparently slightly buckled.
I do not know if this occured at the time of the backfill or later on. We have had a very rainy summer and the soil was slightly damp when we backfilled. I am not sure if this was the reason for the wall to buckle or not.
Another thing I thought might of caused this was the weight of the skidloader pushing down the soil against the wall. When my father backfilled, he drove the skidloader very close to the wall to level so we could place scaffolding along the foundation. I thought this might have pushed in the wall???
I am just looking for opinions of what mighthave caused this and also the best way to go about fixing this problem the correct way. I figure the backfill will need to be removed, the floor joists will need to be braced, and a new block wall will need to be put in. If I do this, I figure it will be best to backfill the entire trench with gravel.
If you know of any other better ways to go about this, I would greatly appreciate this. I have alot of money into this house, and I don't want further complicate the situation.
I have not installed any windows, drywall or plumbing yet so that is one positive.
Thanks for any advice you can offer.