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Bidding retaining wall in sandy hillside

Discussion in 'Landscape Architecture and Design' started by Doster's L & L, Aug 11, 2004.

  1. Doster's L & L

    Doster's L & L LawnSite Senior Member
    Posts: 616

    i got a call to build a retaining wall on a sandy hill. The hill is about 9' at the highest point (a small section) and it is averaging about 7' high. Ofcourse i want to do a 2 tier wall, but is the sand going to be stable enough to hold the weight of the stone? Should i pour concrete w/ rebar as my foundation or will limestone rock be sturdy enough?

    I planned to build the bottom tier 4'high. Then on the top tier, i would go along the contour with the stone and build it as high (5')or low (3')as needed . There are some spots that will get filled in to keep it from looking "jacked up".

    This is going to be a rather large project, but bidding it is new to me. I figured that i need appx 2100 blocks (16"x6") or 1440 ftsq of the blocks. This is going to be a cost of $18,750 for the customer. I'm thinking that i will double this price and that will include digging the hill and foundation, pouring foundation, laying the stone, back filling, laying perforated pipe, ect. This should take a week to finish with a couple of guys helping. What do you think? Decent pricing plan? or not?

    Any tips on the job are appreciated too.
  2. D Felix

    D Felix LawnSite Bronze Member
    Posts: 1,898

    Even if you aren't planning on using them, pick up a Keystone installation manual. It'll get you in the ballpark for installation procedures.

    I would not pour a concrete "foundation" for a block wall. At a minimum, it needs to be below frost line, which around here, is 32" below grade. If it's not below frost line, when it freezes, it will heave and crack. A gravel base will be able to flex enough that it will not throw the wall out of alignment or off level.

    Rule of thumb for terracing walls like you describe, is the upper wall needs to be behind the lower wall by twice the hieght of the lower wall. So if you have a 4' high wall, the upper wall needs to be 8' behind the lower wall.

    At 4' high you will need at least one layer of geogrid behind the lower wall, with sandy soils, I'd be leaning more towards two layers.

    Ask your block supplier for help in designing/spec'ing the walls. They should have someone who is capable of doing so. Unless you are buying your block from a garden center or Lowe's/Home Depot, etc.

    As for bidding, that's not how we would go about it.....

    Figure materials (EVERYTHING!!), equipment, and labor. Figure labor by how long you think it will take and multiply that by your hourly rate.



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