Have just finished excavating two large holes in rocky soil for two new 4′ X 4′ basement slider windows in a cement block foundation and their window wells.
The excavations are about 8′ X 5′ X 7′ deep (approx. 10 cubic yards each). Rocky soil. The finished window wells will be about 5′ X 4′ X 4′ deep. So on balance I’ll need to put back in approx. 5 cubic yards of fill + a stepped retaining wall. The fill will be about 3′ deep in the bottom of the hole and 1′ – 2′ behind the new retaining walls (sides of the hole).
Can I use the rocks I just took out for the fill if the dirt is removed? Most of the rocks amount to say 4 – 6″ in diameter. Is there some good reason to buy 3/4″ gravel instead of just putting rocks back in? From what I can gather, the reason for using gravel instead of soil is because gravel wont retain water. Rocks wont either. The fill isn’t going be a bearing surface, it is just for drainage.
Is there an issue with freeze/thaw? (the house is in NY state). Would gravel be more likely to absord the expansion of surrounding earth better than larger rocks, helping to preserve the new retaining walls?
Thanks in advance,
Mike
Replies
Better to use the dirt if the rocks are removed.
Gravel is a mix of aggregate of varying sizes, with the smaller pieces filling the voids between the larger ones. If all you used was the large size aggregate you have, there would be nothing to fill the spaces. Soil placed on top of them would eventually filter down with the rains and fill those spaces, possibly creating holes in your surface.
I try to avoid having rocks larger than four inches right next to the foundation, especially with CMUs. Frost pushing an eight inch stone donut can cause a high point load of force and create breaks in the block or mortar. You will have already weakened the wall with the addition of this window so you don't want to chance that. Try to place the stone you have so it is at least the same distance from the structure as the diameeter of the stone. Use gravel next to the wall.
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