Moist/wet soils under foundation 2

[joenorm]

I am wondering if soils under foundations are typically assumed to be wet? They are in the earth, after all.

We make foundation drains, but is the point of these to keep the the supporting soils dry? Or to keep bulk water out of the foundation for other reasons?

I am still trying to understand if water migrating underneath a footer/beam foundation is a structural threat, or just inconvenient(mold, not nice to work in puddled water, etc)

Soils are sandy clay. Non-expansive as far as I know.

 

[r13]

I remember you have mentioned encounter sand layer in a shallow depth. I think it is better to dig a trench behind your house with good slope to divert the water away. The trench should be at least a few inches deeper than the sand layer, so it wouldn't fully inundated by the runoff. If this cuts off the water flow at the crawlspace, then you are good to make further improvement.

 

[joenorm]

I have not encountered sand in this particular area. Sandy/rocky clay, and that is part of the problem. I mentioned sand because basically above and below my house area footprint is mostly sand. I seem to have built on a clay island in a sea of sand.

 

[MTNClimber]

I would not advise putting in poly around the building. From what I've been told, it was attempted on several projects where the structure was placed on moisture sensitive soils. Apparently it trapped a lot of moisture and created issues in crawlspaces (mold and flooring issues) and in some cases made the foundations move. I'm not sure why that would happen since theoretically its very similar as capping with low perm soil but the practice of using poly around a building has been abandoned in my neck of the woods.

 

[r13]

Then, don't bother to dig down to any layer, just a trench deep enough not letting the runoff to flow over. Or, build clay berm as suggested.

 

[r13]

Just an idea. The berm needs not to cover up the crawl space *which could be much higher than shown), you may adjust the height to fit your need. The ditch can be filled with gravel to protect the toe of the berm.

 

[joenorm]

Thank you for the drawing. What exists currently is essentially what you've drawn, but without the berm.

So most of the water coming toward the ditch(6 inches lower than footer)gets taken away, but with heavy rain there is quite a bite still making it into the crawl.

What I do not know if this is water coming from above, or water coming from the side that is overtaking the ditch drain.

It almost seems like an underground flow.

Appreciate all the feedback

 

[r13]

Since your house is on the hill, for an intense rain fall even in a short duration, overflow may occur. Make a small berm (6" say) to test if the overflow stops. Also, another source of water infiltration is from the wind side of crawlspace opening, depending on how height is the crawlspace. Come back and let us know if the problem persists after all these efforts.

 

[oldestguy]

If questions still remain (apparently) as to really what is going on, I'd like to see some side view cross sections. And as to water flowing in the ground, it is common if water flows over the surface, it also is moving under the surface,about the same direction, but slower.

 

[joenorm]

The soil around the wet area is certainly softer than the soil around the more dry portion. But I suppose that is to be expected with clay?

I am guessing the problems associated with these sorts of situations are over the long term? Years of wetting and drying cycles could shift things a bit.

 

[joenorm]

I started digging a little sump pit in the crawl space today and noticed I was carving through layers of pretty dry, dense, hard, clay.

As I dug the moister only seemed to enter from the top where there is a bit of standing water.

Tried to attach images but not sure if it worked.

 

[oldestguy]

As to long term changes, I'd not expect that unless some work is done to make things different. I seldom see these problems (or solutions),changing significantly overtime.

 

[joenorm]

OG-

Do you mean to say the problem will stay the same unless addressed or that things will likely not get any worse?

 

[oldestguy]

Likely no significant change with time. That's from this 91 year old very old guy.

 

[r13]

joenorm,

Take the old man's advice, don't worry too much about the top soil condition, unless erosion has occurred.

Dig the trench and build the berm, water shall stop to get in the crawlspace. Then you can cover the crawlspace with vapor barrier, and add sand as weight to hold the barrier in place.

 

[oldestguy]

This old guy reviewed this post and, in line with a recent post, I ask what is the actual experience of these guys? My bet is darn little. Have they ever done the steps I see they expound about? Ask the question and if not directly answered, the answer is NONE.