Hey everyone, I'm a total newbie to this and I could use some guidance! I'm in the process of building a 50-foot retaining wall that's about 3 feet high, and trust me, it's been a workout just digging a trench that's 50 feet long, 1 foot deep, and 20 inches wide! I plan to fill it with compacted 3/4 inch gravel.
Now, I know I need to add a drain behind this wall, but I'm confused about how to slope it correctly. From what I understand, the drain should be placed behind the first block base, which needs to sit on a flat layer of backfill gravel. If that's the case, how do I achieve the necessary slope when the surface is flat? Would it work if I began the drain at 6 inches in height?
Also, I'm wondering if I can just use a flat drain with weep holes throughout instead? I'm considering using T joints and placing the wall drain about every 5 feet. Would that even require sloping? Lastly, regarding fabric, can I use the non-woven heavy fabric from Home Depot in 4-foot vertical strips, or do I need something wider? Just trying to make sure I get it right!
2 Answers
Since you're going 50 feet, using a slanted drain should work fine with a 1 inch perforated pipe. Just make sure it runs downwards; a 10-foot run should be enough. If you're thinking about weeping holes every 5 feet, I’d say that’s a great idea to let the water out without the need for extra slope.
Hey there! Sounds like you're doing a lot already. As for your blocks, if they’re about 70 pounds and measuring 6 inches tall, you might want to dig a deeper trench for better stability. When it comes to the drain, using a 6 inch perforated pipe wrapped in sock cloth is a good choice. You could also shift to smaller pea gravel for better drainage performance.
Yikes! That’s not exactly what I was hoping to hear. Just to clarify, the blocks are pretty big – around 70 pounds each and roughly 6x16x10 inches. The trench is 20 inches at the narrowest, but the hill does slope back about 6 to 12 inches to the top.
Got it! So, I'd just need to add a bit more gravel at the highest point under the pipe. Do you think I’ll really need those wall drains every 5 feet?