Retaining wall - hard clay base.


  #1  
Old 07-14-09, 05:27 PM
T
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Question Retaining wall - hard clay base.

I am building a retaining wall using retaining wall blocks. I have dug a trench about 20" wide and 7" deep. I am hitting some pretty hard clay in the bottom of the trench so far. I have debated whether I should just stop at 6" deep or get a sledge hammer to break up the soil and go deeper. The wall will be under 36" tall.
A couple other questions:
1. I am trying to figure out a way to determine if the trench I am digging is level throughout the length of the trench. It is about 24' long. What's the best way to make sure the trench is level before adding in the base material.
2. Any recommendations on what material to use for the base? I have heard sand, pea gravel, stone dust etc.

Thanks.
 
  #2  
Old 07-14-09, 08:36 PM
B
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The clay can be a pain. When weather is dry, it is solid. When wet, it turns to putty. If you are in frost country, it will hold the water/moisture and shift when it freezes.

As for level, put a post in at each end, nice and solid about a foot above the trench. Pull some masons twine (it stretches) or nylon fish line from post to post. Nice and tight and make it level or at least level with your design. Now measure from the string down to the bottom of the trench.

As for a base material, I like a good gravel. Something that will allow the water to drain. Of course it has to have a place to drain to, which sometimes involves continuing part of the trench with gravel or piping to a lower level where the water can drain.

Good Luck
Bud
 
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Old 07-15-09, 04:58 PM
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Thanks Bud, that was helpful. You mentioned that the clay can be a pain since it can get soft when it rains. So do you recommend I dig the trench deeper than 7" that I have now? Is the idea that since it gets soft with rain that I need to provide a deeper bed of stone?
thanks.

Tim
 
  #4  
Old 07-15-09, 05:21 PM
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Unknown what you will find if you go deeper, could be just more clay. If you don't have frost to deal with, what you are planning is probably good. The beauty of dry stack blocks, is they can be re-stacked if problems arise.

If you have frost, the whole process needs to be re-worked for drainage behind and below your project.

GL
Bud
 
 

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