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Discussion Starter · #1 ·
Altho rock hard in summer, here in Oregon, it seems it might be very porous and sandy when wet.....

Can heavy rains soak down into wet clay for 3-4-5 feet ? Is that possible ?

Thank you
 

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Discussion Starter · #3 ·
Hi Nik, neither building or growing. I started a thread 1/22 about water in my crawl space. Inspections revealed no gaps in the foundation and rain probably did not enter via the foundation vents. That leaves porous red clay as the main suspect......
 

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The short answer is yes, given enough time and water it will soak all the way down to the water table.
Ultisols can have a variety of clay minerals, but in many cases the dominant mineral is kaolinite. This clay has good bearing capacity and no shrink–swell property. Consequently, well-drained kaolinitic ultisols such as the Cecil series are suitable for urban development.
https://en.wikipedia.org/wiki/Ultisol

From my experience red dirt is good to build on but you have to be aware of what is going on geologically is the top layer of clay sitting on limestone or granite? this is where geotechnical engineering comes into the picture. typically before a subdivision is built the geotechnical company comes out and drills core samples in a bunch of places and they make a report on it which is then filed with the zoning and planning office. I would check with your local building departments to see what kind of geologic maps they have of the area.

here is an example map.



edit: just wanted to point out that all soil types can fail to support a structure if water is not managed correctly.
 

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Discussion Starter · #5 ·
Thank you for your reply. Our well driller's log from 1993 says: first 5 feet is red clay; next 10 feet is brown clay/cobbles. Last 100 feet is black and white granite.
 
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