block retaining walls
Allan blocks are cementious blocks for retaining walls that do not use mortar. They are stacked, w/ either polyethelyne clips or other method for connecting one block to another. The wall resists falling over by its weight, its lean (I can’t remember the official term for the amount off of plumb the wall is), and optionally the use of a mesh-like material extending back into the earth. Usually the first 12″ behind the block is 3/4″ gravel, which facilitates drainage and prevents ice heaving. Getting the first course perfectly square and level and plumb is critical, be/c each course above will exaggerate any “flaws” in this.
I’m used an alternative brand from Mesa and was thrilled w/ the results. Your dimensions are well within what’s possible w/ these blocks. They are certainly worth the time for your research. Lowe’s, etc offers some. But I went to my material supplier (Metromont here in the south) and was happier w/ the selection and advice.
Does anyone know where I can look up footing sizes and rebar size and spacing for 8" concrete block retaining walls of various hights. I know that soil conditions and hydrology make a difference but I'm just looking for generic guidelines. Thanks.
*Why don't you use Allan Blocks? What is the maximum height. What type of soil? Look in "Building Construction Illustrated" it gives a general outline for retaining walls. Make sure however you build it you put drain tile behind it. Use 15m rebar for verts and horizontals.
*A mason buddy showed me book of details of mas. constr. Probably from mas. institute or org. I'll see if I can get a name and e-mail you.
*Many thanks for the info. The maximum hight is 6', the soil is clay, and I was planning to install perforated drain pipe and drain rock. I was interested in the appropriate width and depth of the footing and the horizontal and vertical spacing of the #4 rebar. What are Allan blocks?
*Allan blocks are cementious blocks for retaining walls that do not use mortar. They are stacked, w/ either polyethelyne clips or other method for connecting one block to another. The wall resists falling over by its weight, its lean (I can't remember the official term for the amount off of plumb the wall is), and optionally the use of a mesh-like material extending back into the earth. Usually the first 12" behind the block is 3/4" gravel, which facilitates drainage and prevents ice heaving. Getting the first course perfectly square and level and plumb is critical, be/c each course above will exaggerate any "flaws" in this.I'm used an alternative brand from Mesa and was thrilled w/ the results. Your dimensions are well within what's possible w/ these blocks. They are certainly worth the time for your research. Lowe's, etc offers some. But I went to my material supplier (Metromont here in the south) and was happier w/ the selection and advice.
*Allen blocks are open in the middle. Think about concrete wall blocks with a rough finish to the outside. The blocks are lighter than solid blocks but require that you fill the voids with washed rock. No fines. This provides additional drainage. When you build your wall also allow a minimum of 12" behind the wall for drainage. Apply landscape fabric to your clay soil and fill the gap between the wall and fabric. Lay the fabric down on the second last row of the wall and top off with soil. The fabric will prevent migration of the soil into your clean rock drain area. Most of the wall systems I am familiar with do not require rebar. They use pins or other devices between the blocks to lock them together. Allen uses a lip on the front of the block which causes each succeeding layer to be moved back thus causing the wall to "lean back" and prevent overturning, the most common block wall failure. I recommend that you talk to your city/county permit folks. They may have information/requirements on building walls and could require you to submit a drawing with elevations and the product you intend to use in order to get your permit. Depending on your building codes, the drawings may need to be "sealed" by a Professional Engineer or Architect. Six feet is not a high wall but may require preloaded fabric back some distance. Contact the various manufacturers/distributors of wall block in your area. They will have free information and good advice on the application of their sytems. Costs can vary greatly by product. Also plan on providing a good base for your wall. Compact the clay in your trench with a compactor, add 1" minus material in layers and compact that as well. See your selected block manufacturer or building code specifications for the depth. Check each block in each course for level. It is easy to have errors build if you are doing a long wall. Sorry for the length of my response, I gave you more than you asked for.
*I just finished a retaining wall that was 2.5' high x 45' long using the type of dry stack block discussed above. It took 2 labors and myself 4 hrs start to finish. The kind sold at Lowes, etc, generally are the smaller ones that are not good for going more than a few feet high. A good rule of thumb is that the heavier the block, the higher you can go to with the wall. The grid referred to above is called geogrid (sp?) and I bet an Internet search could find you the info. Here is the web page for the type of block that I used. Click on "Products" and then "Keystone". We used a laser to lay out a footer of a dry sand/mortar mix - which was some left over stuff I had on the job. We put washed gravel, ABS drain tile, and filter fabric behind the wall. The wall I built cost about $6.50 per square foot of wall face - materials only. That included the bottom course that was burried below grade. I'm gonna guess that the availability of different brands is regional. I live in NC.Good luck.
*For footer size...generally:Width = 2x wall thicnessDepth = wall thicknessan 8in wide block needs 16in wide and 8in deep footing with the block centered on the footing
*For a block retaining wall I had to build an engineer suggested to dig back into the bank and pour a 3-4 foot wide footer.Then lay the block on the outside edge,with rebar and poured cores. The idea being the weight of the dirt will put pressure on the footer and hold the wall upright. Whereas a narrow footer will get kicked out by the pressure.Made sense, time will tell.