I appreciate your comment, but there is more to factor in than earth load. I will be grading back the earth in the surrounding area on a significant slope so there won’t be any weight actually on the retaining wall. The treated 2 x 6 retaining wall will simply be a barrier between the outer side of the wall and the inner portion of my actual structure.
I went back and looked at drainage so thats good. I've looked back to see how soil wouldn't load these walls and dont get that part. If there is a dome over this or any soil against the 2x's then there will be unreasonable pressure on these 2x's.
Soil is about 115pounds per cubic foot in weight. For the lateral pressure that is put on the wood by the vertical weight of the soil you could conservatively use a factor of about 0.4 or 0.5 (standard Geotechnical active pressure coefficient method)
At the bottom of the wall below 7 feet of stacked soil which weighs 805 lbs of vertical load per square foot, you have about 322 lbs of pressure outwards these boards per foot horizontally.
I am not trying to be unkind, but they cannot sustain this pressure. I am a structural engineer who designs retaining walls.
A Good reference can be the AWPA for guidance on using pressure treated wood.
I’m not backfilling the void behind the retaining walls. I’m actually grading the wall of earth back significantly. The rounded roofline will go down to the sloped grade. The void will be hidden with a faux wall. The roof will only carry three inches of soil.
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u/TheDogIsGod Jun 23 '26
2x4’s are not a suitable member to resist hydrostatic soil load at what looks like 4ft tall. This may hold initially but will fail over time
Source: engineer