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I have a really long concrete driveway, and we'd like to turn the back half of it into part of the backyard. From this:

enter image description here

To this:

enter image description here

I'm hiring a demolition contractor for this task, but I'd like to ask here first to be well-informed about potential issues. The only 2 I can think of are:

  1. We have a sewer line coming out of the side of the house and out to the street under the driveway concrete. You can see 2 circular entry ports leading to it (does this mean 2 pipes?). Is it safe to remove the concrete and keep this sewer pipe buried under the grass? Or would I need to add some sort of protective layer in between? Can I put down a lawn on top of this pipe?

enter image description here

  1. We have a retaining wall with the neighboring driveway that's leaning out a little bit. Does it need the driveway concrete to stay upright? Is it likely to collapse if the concrete is removed and replaced with grass? It's very short, from 6" to about 18" towards the back.

enter image description here

  1. Are there any other issues or concerns I should take into consideration before hiring a contractor to demolish the driveway? Foundation damage, gas lines, etc.? This is my first big project, and I don't want to rush into this without asking around for things to consider that I haven't thought of. This property is in Portland OR, and the house was built in 1918. Are there any city regulations, permits, laws to worry about?
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    Dude... that's totally a Photoshop, I can see the pixels! :D :D Actually, it's an excellent representation of what you're after, thanks for posting it. Many properties all around the country have all sorts of lines buried under the lawn and aren't protected by concrete. Before your contractor starts to dig it up, they'll call a utility location service (811) to mark everything that's underground - sewer, city water, gas, electrical, cable, phone, whatever so they know where it is and how deep it's buried. They'll know how to work around them.
    – FreeMan
    Sep 1, 2021 at 21:54
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    It's possible that some things may have to be buried deeper because they're no longer protected by the concrete, so bare that in mind. For example, electrical in conduit can be about 6" under the concrete, but needs to be at least 12" (or 18", depending) under dirt. You might have to get that line moved if it's there.
    – FreeMan
    Sep 1, 2021 at 21:56

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  1. The sewer and storm lines are usually deeper than few feet from the grade. If they are buried too shallow, you might need to drop them lower to receive adequate topsoil, and place thermal protection over them to act as a protection for frost. Unless you intend to place heavy items directly over the buried drain lines, no special protection is required.

  2. Similar to the above, for a properly constructed earth retaining structure, the bottom of the footing should be placed at or below the local frost line. Also, no retaining structure shall rely on the toe side soil to maintain stability. If you are the owner of the retaining wall, you can do whatever you wish. If not, don't touch it, and use hand excavation near the wall instead of using a machine. Be prepared, you might need to stabilize the wall before putting the soil back. However, I doubt you'll have such need because your excavation shouldn't be more than 2'-3' deep (the thickness of the slab included).

My suggestion is to dig a few exploration holes to verify the depth of the drain lines and the retaining wall foundation. Also, most importantly, check with the local utilities to make sure there is no utility lines buried below, or ask them to mark the locations if there are such installations.

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  • I would suggest that dirt is likely a better insulator than concrete so if sewer/water lines were too shallow, they'd already be a problem. Also, from the pics, it appears that there's nothing but concrete from front to back on this part of the property, how should the OP "dig a few exploratory holes" through it? It's my understanding that once the utilities are marked, they know how deep they are since they're put in at reasonably standard depths.
    – FreeMan
    Sep 2, 2021 at 12:41
  • @FreeMan The sewer line can be right below the pavement in regions without frost potential. If the OP can't perform the digging that requires breaking the concrete, let the contractor do it before excavate blindly if no other information is available. Thanks for correcting the mis-spelling though.
    – r13
    Sep 2, 2021 at 13:28

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