I want to build a retaining wall, but I can't find consistent information as to the measurements of the trench. I'm using interlocking blocks that are 16" wide, 6" tall, and 12" deep (from front to back). The wall will be 30" high including the first row which will be mostly underground.

How deep and wide should the trench be, and how much gravel do I put underneath the first row of blocks? I'm thinking of making the trench 10" deep and putting 6" of gravel down so the first row of blocks will be 2/3 underground. I'm also thinking of making the trench 24" wide, so I would need 12" of gravel behind the first row of blocks. Will this be a problem?

do you have any frost/freeze concerns? i'd check with the city, or the store where you're purchasing the product...wish you could see the guys on diy network...http://www.diynetwork.com/diy/shows_droc/episode/0,2499,DIY_21539_41962,00.html

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