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Retaining wall advice please?

Discussion in 'Hardscaping' started by kaig, Aug 22, 2006.

  1. kaig

    kaig LawnSite Member
    from Lee, NH
    Messages: 9

    I'm admittedly just a homeowner, but I thought I'll see if the pros have some advice for me, and there's a potential for someone to make a little bit of money in this, too.

    I bought a new home (Seacoast, NH) last year which is on a pretty sloped lot. We had some heavy rains after the (late) hydroseeding last fall, and I didn't really get much of a lawn, which made me a hobby landscaper this year -- I admire you guys doing this every day, as it's serious work, but I find it quite enjoyable, too.

    Anyway, I found lawnsite in my quest to learn about lawns, stumbled upon the hardscaping forum and found a lot of real nice work here. So I decided I want to put in small retaining wall, for one because I like the looks and would like to learn how to do it (always up for something new). To justify the expense and effort, I'm telling myself it should also be helpful in dealing with the erosion problems on the slopes. Now, I'm not much of a promising customer, as, like I said, I'm in it for the experience of doing it myself, and neither could I afford spending a couple of thousand of dollars. In the pic below, the steepest slope is in the front left, about where I put in a couple of blocks just to get a feeling for how it would look (no base, no drainage etc at this time, but I will be doing it right).

    In order to save expenses, I started to scrape of the existing top soil (will reuse later), and I want to just redistribute the fill (sand with bricks is what I've found so far), not bring in or haul out more stuff. However, I will obviously need the blocks, gravel, base material. If any of the NH guys here are interested in just selling me the materials (+ delivery), I might be up for that (I suppose you get stuff at a discount, so you may make a bit of money without any actual work).

    And then I have a couple of questions, too, any kind of input would be appreciated.

    For one, the wall is next to a patch of wooded land which was saved during the construction. However, the builder piled up fill right next to some of the trees to build up the slope, so I suspect they may be doomed anyway. I suppose by removing some of that close fill and then putting in the wall at some distance, I'm at least not going to make the situation worse?

    2nd issue, on top of the hill in front of the house is the septic leach field. I'll be pretty far away from it (the wall will go only about 30' back, which is roughly where the field starts, but I'll be at the foot of the slope while the field is obviously in the flat part on top). Just want to make sure I'm not potentially overlooking any issues there?

    The wall will be maybe 4' high at the highest point (front left), lower in the back, as the terrain (wooded patch) slopes up, so I don't think I have any engineering / grid issues. Does anyone know NH rules on engineering, permits, etc?

    How do you guys go about designing/estimating height & materials? If it were a straight wall at given height/length, that'd be quite easy, but as I said, I want to keep the net amount of soil/fill the same, and it seems not easy for me to guess at what distance from the wooded patch the wall should be, how high, how to taper it off at the ends or turn it in, etc.? Any tips on that, or is that just what comes with your experience? I'm currently thinking I'll just form the new shape with shovel, wheelbarrow etc until it looks right to me, and then see how tall / long the wall is going to be and order materials accordingly.

    I'm planning to do basically everything with handtools, which actually seems quite doable, even though it'll take quite a bit of time (but saves on the gym ;) The one thing I'm wondering about is a plate compactor, how necessary is that over handtamping? The problem is, this is going to be a weekend project which will take a while to finish, and renting a compactor a couple of times sounds quite expensive, besides I'm not really quite sure how to haul it -- I assume these things are too heavy to be moved by a single person?

    Finally, though I should have asked that first, is a wall going to look good there? And is it going to help with the erosion?

  2. XXL Hardscaper

    XXL Hardscaper LawnSite Member
    Messages: 37

    You need an Engineer......what you have there is already wrong

    Walls are not meant for erosion control!

    you have no footer.....you have no courses of block in the ground.

    A 4 foot wall with that slope at the top and fill dirt at the toe needs to be designed by an engineer!!!!!

    You need soil tests, global stability test, gravel for the footer ( yes compacted with a plate or jumpinjack ), drainage gravel, drain pipe, geo grid, filter frabric and a set of stamped drawings.

    The only thing I see is alot of bad soil and some block
  3. kaig

    kaig LawnSite Member
    from Lee, NH
    Messages: 9

    Alright, thanks for the reply, I hope you're willing to get into more detail, though.

    Why do you say walls are not meant for erosion control? They obviously allow for less sloped soil areas, thus less run-off / washout. I mean, imagine I built this whole thing up 7' so that the top and bottom were exactly level. That would fix pretty much all erosion, wouldn't it? (Not that I'm intending to do that, I just want to lessen the slope to what it's further back, where the current slope seems to be holding just fine even though the grass on it is still spare, too).

    I know I have no footer -- I actually do have a half a block in the ground, but that's really irrelevant, as I wrote above, I just put these blocks there to get a feel for what it would look like. I didn't fill the cores either, nor are they in their final position at all. I'm going to put a base (on top of undisturbed soil) on fabric. I'm going to put drainage stone in the cores and behind the blocks. I'm not sure I'm going to do a drainage pipe -- according to the manufacturer it's not needed for this size wall, but I may do it anyway.

    Since I'm moving the fill I'm cutting out in front of the wall behind it, the slope behind the wall will actually be level for a couple of feet. Besides, even for a slope behind the wall, the manufacturer allows for a 5 ft wall without geogrid (for sandy soil, which I have, besides the bricks in it, but I don't think they're particularly destabilizing at all). I believe that's a good idea for drainage -- otherwise, the run-off from the area above would just collect right behind the wall caps with no place to go. By having a few feet behind the wall level, it'll still pool there, but more spread out and it will have a larger area to percolate through. Does that make sense?

    So, you guys would feel uncomfortable to build this kind of wall without an engineer's approval? Again, I'm just looking to ease the slope, not eliminate completely, it's not a very tall wall at 4' in the front and ~ 2' in the back.
  4. DVS Hardscaper

    DVS Hardscaper LawnSite Fanatic
    Messages: 6,602

    U sure bout that?????

    Absolutely walls can be used as a form of erosion control.

    Mr. Homeowner - your best bet is to contract with a competent, experienced professional. Check their references, visit their jobs, and go back 3-5 years with their jobs/references. New jobs always look nice....
  5. XXL Hardscaper

    XXL Hardscaper LawnSite Member
    Messages: 37

    DVS you apparently do not deal with many civil or geo technical engineers, I on the other hand I do. I called my Uncle who designs the walls that I have built before I responded to what you said. Erosion control and water remediation is not there design, it may be an indirect result of the wall but not the reason. If an engineer is contacted for erosion control they will never spec a wall to take care of that issue. What I gave was sound advise, CALL AN ENGINEER. Do not start with a contractor , I don't care what there experience is, It will cost you less in the long run.

    Mr. Homeowner as you refer to him wants to build this himself DVS Hardscraper, so the advise and things I mentioned are sound. The advise you gave was flawed, never mind you didn't even give any advise to his wants and needs..........Typical :laugh:
  6. Mike33

    Mike33 LawnSite Bronze Member
    Messages: 1,649

  7. Mike33

    Mike33 LawnSite Bronze Member
    Messages: 1,649

    I think he was just stacking them to see what they look like, i have done that for customers at times when im bidding. I think srw and do them for erosion controll. 4' doesent hardly have to be enginered give me a break. It does require geo-grid though. I think your uncle justs wants your business. I use allen block and im not going to start a pissing contest of what is the greatest block. My factory rep who has seen around 20 of my 180 plus walls has seen my process how i install. she like my work and says i over kill with grid and gravel which made me feel good. Also stated with my experience that i dont need to contact them, but they could get me an engineer if needed for larger walls. I was bidding one last year for a homeowner 25' in height my rep met with me and homeowner and said this would require one.
  8. GreenMonster

    GreenMonster LawnSite Silver Member
    from NH
    Messages: 2,702

    b4 you do much more digging around there, you might want to call 1 888 dig safe.

    Compaction (plate/jj), geo-grid, drainage, 3/4" cbr, angular drainage stone, are all NECESSARY ingredients to build the wall that you're describing. An engineer..... I believe that might be a little overkill for what you're talking about, but certainly a 4'+ wall with a slope behind it and questionable soils has some special considerations.

    If you really want to do this yourself, I would definately recommend learning the proper methods for installation, otherwise you'll have wasted a lot of time and money on a wall that will likely settle or even fail in the future. If you decide you might want to hire a capable contractor, give me a call, I work in your neck of the woods. I'm in the YP.
  9. crab

    crab LawnSite Senior Member
    Messages: 633

    what you need is shrubs to cover up those ute boxes. i really don't see why continuing the grass slope wont work.civil engineer much to vulgar display of power.
  10. XXL Hardscaper

    XXL Hardscaper LawnSite Member
    Messages: 37

    Mike I am not doubting your expertise in walls. I know that in the counties in which I work that there are height restrictions for non engineered walls. 1 county is as short as 30", so in that county you need stamped drawings to obtain a permit to build a wall that is less than 3 ft. It all depends on were you work and whether or not you do things by the book. There is a contractor around here who will build 5 and 6' tall walls with no engineer, no grid, In proper drainage, and allot of glue. Thats not me, do it right or don't do it.

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