Virgin Soil


Old 07-09-03, 06:19 AM
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Join Date: Apr 2003
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Virgin Soil

After much delay, I am finally striking ground for my deck project.

For those who don't remember my posts a few months back, when I submitted my deck plans to the local township, they informed me that my lot was built up from a lot of fill, and that the footers on my house at one end were 9' deep.

I was told I had to put the piers for the deck on virgin soil, and by the township engineer's estimate, it should be 5-6' down until I hit it. I am still sketchy as to how I am to know if I've hit virgin soil or not. so far I've been told that you've hit virgin soil when:

1. The dirt starts to come out and it is very loose, not stuck together in little balls like the fill.

2. It will become much harder to dig into.

The apparatus I am using is a bobcat with an auger and extensions, so I should be able to hit 8' or so if I need to, but I obvioulsy do not want to dig any further than necessary.

What tips can anybody give for knowing when I've gone far enough?

The above info came from the township, but I always get other opinions.

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Old 07-09-03, 06:54 PM
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Join Date: Apr 2001
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Typically, there will be a change in color, consistency, and/or hardness when you reach virgin (residual) soil. You could have only one of these changes, a combination of two of them, or all three. Have you asked the township what the residual soil is like? If not, ask them if the color changes or if the residual soil is sandy, silty or clayey. If it's sandy and the fill is not, then the firmness will noticeably change and you will most likely not be able to make a ball that stays together when dropped out of your hand at a height of aobut 6"-8". If clayey, then you will be able to form a ball that stays together when dropped from that height. If silty, then the soil will form a ball, but you will notice that it is smooth and almost slippery like in your hand. Also, you might want to ask about the water table in your area. It should be fairly easy for you to spot these changes and hopefully you will have a noticeable color change when you hit residual soils which is the easiest way to know for certain that you've dug far enough.

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