Building a retaining wall on a severe slope

Discussion in 'Hardscaping' started by bigslick7878, Jun 6, 2009.

  1. bigslick7878

    bigslick7878 LawnSite Senior Member
    Messages: 809

    Got a job where I need to build a retaining wall on a severe slope,starting at the front of the house to the backyard where there is about a 8-10 ft foot drop over about 50 ft of length.I have done walls on slopes before but not one this steep or even close.

    I am going to step the wall about every 10 ft or so to avoid a high wall at the bottom of the grade,where it should only be about 4 ft high.Probably about a 45 degree slope overall (guesstimate)

    Usually I will dig out the base perfectly level to the lowest grade and build up,but in this situation that would require me going WAY deep and possibly running into a sewer line and other stuff near the highest part by the front.I would literally need to dig down 10 ft and that's just not really practical and a lot of the block would be covered so that doesn't make much sense.

    Could I do it? Yeah I could but that is going to require a massive amount of digging to get the high part of the grade with the lowest and get it level.Looking for other options, I don't like digging near plumbing or electrical and both are close by.

    My question is can I step the base grade (soil) just like I would the blocks and at the same point,and maybe put a cinderblock every 10 feet at the breaks to make sure the soil doesn't shift under it.Obviously I would secure the cinderblock with some rebar or something to make sure it doesn't move underneath and backfill on top.
  2. DVS Hardscaper

    DVS Hardscaper LawnSite Fanatic
    Messages: 6,623

    absolutely, you can step the base course(s).

    We do it all the time. very seldom do our world renowned walls have a base course where the base course is all consisting of the same course.

    Tha purpose of the base course is:
    a) to provide a level platform to obtain a level wall.
    b) to provide a buried layer of block below grade which will keep the wall from sliding forward and collapsing.

    I have no clue what you're talking about using cinder block (properly referred to as masonry wall block, they haven't made "cinder block" since the 70's) and rebar? sounds bizarre. No need to use masonry wall block.

    When finished don't forget to start a "my first" thread!

  3. bigslick7878

    bigslick7878 LawnSite Senior Member
    Messages: 809

    Well it definitely isn't "my first" so maybe I will call it something else.I have done plenty of walls but none with this type of slope.The customer wants me to use block that is very small and undersized (he already bought half in a failed attempt to do it himself) so I want to make sure the base is absolutely perfect and has no issues now or in the future.

    What I am referring to with the block is when I step down the soil just something to sit underneath at the break to hold the above course (of soil) in place (just in case) I know that with the compaction of the dirt at that level underground I shouldn't have anything to worry about if i just shape it but I was just trying to make it bulletproof.It will be buried and I will cut it if necessary to make sure I have some base material on top to sit the wall block on of course.

    I know its probably not needed but I would rather overdo it and not have to worry about anything later down the line.

    The reason why I mentioned the block is because I had another property that had a big slope down into some woods and I used the cinderblock filled with long rebar at intervals to prevent erosion on new soil I was putting down.Probably not needed but again I would rather go the extra mile and know it will last forever.

    Thought I could do the same thing on a much smaller scale underneath the wall if you get what I am saying now.
  4. Bru75

    Bru75 LawnSite Senior Member
    Messages: 582

    That's a helluva big wall to use "very small and undersized" block. If you want your customer to have no problems in the future, tell him that you need to use the proper blocks. He has already proven through his failed attempt that he does not know what he is doing, so why let him dictate the type of block when you know it is not right?
    You mentioned that this wall will be about 4' tall, some of the small block is not recomended for more than 2' or 3' by the manufacturer. Using it for a wall that is taller than recomended could open you up to a lot of legal trouble later if the wall should fail.
    I don't mean to preach to you, just trying to help.
    To answer your original question, just step the footer trench as needed to maintain enough embedment of your wall. No need for the cinderblock, the compacted gravel will hold each step in place. This takes a lot more time than a footer on a single level, so hopefully you have figured that into your price.
  5. bigslick7878

    bigslick7878 LawnSite Senior Member
    Messages: 809

    I hear you.

    After leaving his house and thinking about it tonight I thought the same thing.If I had the choice I would of course do it that way,but I might meet some resistance.

    He seems to be set on using whats already there,mentioning how cheap the blocks were at Home Depot and what not.They are the 8' x 4" little things... (I know I know WTF)

    He has about 150 or so already there,I figured I will need about 500 more.

    If its done right it will probably hold up and I will make it very clear that if I do use that block what the possible repercussions could be down the line.

    I wont guarantee anything,and will undoubtedly give my recommendation about the right type we should be using.

    He will be warned and I will give my professional opinion,thats the best I can do.

    I might try to find some other place on the other side of the house to use that old block so we don't have to "waste" it.He wants me to dig out a mulch bed buffer on that side and the slope isnt as severe....that could work.

    I will keep you guys posted.
  6. Bru75

    Bru75 LawnSite Senior Member
    Messages: 582

    If you can talk him into using it elsewhere or selling it you will both be better off.
    Be very careful with this. I'm no lawyer, but it seems to me that the fact that you have discussed the possibilities with him could be used in court to show that you knew the blocks were too small and used them anyway, if the wall fails. Could be an even bigger problem for you if somebody gets hurt. I'm just not all that sure that your verbal warning would protect you.
    Do you need a building permit for a wall this size in MD? The inspector or engineer might require a larger block. This could work in your favor and force the owner to use the correct block without you having to do the forcing.
  7. bigslick7878

    bigslick7878 LawnSite Senior Member
    Messages: 809

    He is a friend of the family,not some random customer off the street.

    Just looking at the price of the 12" x 8" cheapo's at Home depot and the price difference will be negligible.I dont think I will have any problems going that route at a minimum.
  8. DVS Hardscaper

    DVS Hardscaper LawnSite Fanatic
    Messages: 6,623

    Freind or no friend, walls are not to be taken lightly.

    But if he's a friend, you really wanna do it correctly ywith the correct materials. I do not understand how on earth being friends justify's just wingin it any 'ol way. I could write a book about broken relationships because people used an unqualified family friend to do their hardscape job. Literally.

    And yes, again, the wall can be stepped.

    And again, no need to using CMU.

    About using small block - if we did everything a homeowner wanted us to, we'd would have been sued 50 times by now. You gotta use the right stuff. If you don't, and the wall fails 11 years from now, guess who is liable?

    One thing that upsets me most is when I read on these forums "well the client wants me to use this" or "their friends of mine and they want this". Home owners are not wall experts. They have no clue what could go wrong. They know nothing about materials and methods. Its the responsibility of us professionals to educate them. And if a so called contractor doesnt know what he is doing - then when in doubt....sub it out........
  9. Fordsuvparts

    Fordsuvparts LawnSite Senior Member
    Messages: 517

    Well said i agree 100%, use the right material and the wall and your friends will be good to go.
    I had a friend just a couple of months ago ask me to wholesale him some Keystone block for a wall so that he could have another friend build it, i said let me look at it and he said don't worry about, this guy knows what he is doing. Then last week i got the call to come and look at it, 5' tall wall, no drainage, maybe a pickup load of gravel and no geo grid. Did i mention that we got about 4" of rain in the week follow the wall being built. The estimate to fix it is over 7k and he was not happy so he called around to get proces and then told me man retaining walls are expensive. I said no sh!t

    My guys are going to go over there and stack the block back on to the pallets and then we will shrink wrap them and move them out of the way so we can get the min in there to dig out the mud slide. sorry guys no pictures

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